diff mbox series

[v2,1/1] selftests/landlock: skip ptrace_test according to YAMA

Message ID 20221213185816.3942853-2-jeffxu@chromium.org (mailing list archive)
State Handled Elsewhere
Headers show
Series selftests/landlock: Fix selftest ptrace_test run fail | expand

Commit Message

Jeff Xu Dec. 13, 2022, 6:58 p.m. UTC
From: Jeff Xu <jeffxu@google.com>

Add check for yama setting for ptrace_test.

Signed-off-by: Jeff Xu <jeffxu@google.com>
---
 .../testing/selftests/landlock/ptrace_test.c  | 34 +++++++++++++++++++
 1 file changed, 34 insertions(+)

Comments

Mickaël Salaün Dec. 15, 2022, 6:34 p.m. UTC | #1
This is much better! We can tailor a bit more the tests though.

On 13/12/2022 19:58, jeffxu@chromium.org wrote:
> From: Jeff Xu <jeffxu@google.com>
> 
> Add check for yama setting for ptrace_test.
> 
> Signed-off-by: Jeff Xu <jeffxu@google.com>
> ---
>   .../testing/selftests/landlock/ptrace_test.c  | 34 +++++++++++++++++++
>   1 file changed, 34 insertions(+)
> 
> diff --git a/tools/testing/selftests/landlock/ptrace_test.c b/tools/testing/selftests/landlock/ptrace_test.c
> index c28ef98ff3ac..8565a25a9587 100644
> --- a/tools/testing/selftests/landlock/ptrace_test.c
> +++ b/tools/testing/selftests/landlock/ptrace_test.c
> @@ -60,6 +60,24 @@ static int test_ptrace_read(const pid_t pid)
>   	return 0;
>   }
>   
> +static int get_ptrace_scope(void)

Please rename to get_yama_ptrace_scope().

> +{
> +	int ret = -1;
> +	char buf[2];
> +	int fd = open("/proc/sys/kernel/yama/ptrace_scope", O_RDONLY);
> +
> +	if (fd < 0)
> +		return 0;
> +
> +	if (read(fd, &buf, 1) < 0)
> +		return -1;
> +
> +	buf[1] = '\0';

You can replace that with `char buf[2] = {};`


> +	ret = atoi(buf);
> +	close(fd);
> +	return ret;
> +}
> +
>   /* clang-format off */
>   FIXTURE(hierarchy) {};
>   /* clang-format on */
> @@ -69,6 +87,7 @@ FIXTURE_VARIANT(hierarchy)
>   	const bool domain_both;
>   	const bool domain_parent;
>   	const bool domain_child;
> +	const int  yama_value;

Please rename to yama_ptrace_scope_max and remove the extra space.

>   };
>   
>   /*
> @@ -93,6 +112,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_without_domain) {
>   	.domain_both = false,
>   	.domain_parent = false,
>   	.domain_child = false,
> +	.yama_value = 0,
>   };
>   
>   /*
> @@ -110,6 +130,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_with_one_domain) {
>   	.domain_both = false,
>   	.domain_parent = false,
>   	.domain_child = true,
> +	.yama_value = 1,
>   };
>   
>   /*
> @@ -126,6 +147,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_parent_domain) {
>   	.domain_both = false,
>   	.domain_parent = true,
>   	.domain_child = false,
> +	.yama_value = 0,
>   };
>   
>   /*
> @@ -143,6 +165,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_sibling_domain) {
>   	.domain_both = false,
>   	.domain_parent = true,
>   	.domain_child = true,
> +	.yama_value = 2,
>   };
>   
>   /*
> @@ -160,6 +183,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_sibling_domain) {
>   	.domain_both = true,
>   	.domain_parent = false,
>   	.domain_child = false,
> +	.yama_value = 0,
>   };
>   
>   /*
> @@ -178,6 +202,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_with_nested_domain) {
>   	.domain_both = true,
>   	.domain_parent = false,
>   	.domain_child = true,
> +	.yama_value = 1,
>   };
>   
>   /*
> @@ -196,6 +221,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_nested_and_parent_domain) {
>   	.domain_both = true,
>   	.domain_parent = true,
>   	.domain_child = false,
> +	.yama_value = 0,
>   };
>   
>   /*
> @@ -216,6 +242,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_forked_domain) {
>   	.domain_both = true,
>   	.domain_parent = true,
>   	.domain_child = true,
> +	.yama_value = 2,
>   };
>   
>   FIXTURE_SETUP(hierarchy)
> @@ -232,9 +259,16 @@ TEST_F(hierarchy, trace)
>   	pid_t child, parent;
>   	int status, err_proc_read;
>   	int pipe_child[2], pipe_parent[2];
> +	int yama;

Please rename to yama_ptrace_scope.


>   	char buf_parent;
>   	long ret;
>   
> +	yama = get_ptrace_scope();
> +	ASSERT_LE(0, yama);
> +
> +	if (variant->yama_value < yama)

if (yama_ptrace_scope >= 3)

> +		SKIP(return, "unsupported yama value %d", yama);

"Yama forbids any ptrace use (scope 3)"


This check skips the whole test, whereas the issues with Yama are about:
- a child process tracing its parent;
- the PTRACE_TRACEME case.

I think the main remaining parts to change is the `if 
(variant->domain_*` checks to extend with the yama_ptrace_scope_max check.

However, it is useful to highlight that a test didn't fully covered 
Landlock checks. I think the best approach is to call SKIP() at the end 
of TEST_F(hierarchy, trace) if yama_ptrace_scope >= 1 . This way, we 
test as much as possible (Landlock and Yama) and we mark the "tampered" 
tests as skipped.


> +
>   	/*
>   	 * Removes all effective and permitted capabilities to not interfere
>   	 * with cap_ptrace_access_check() in case of PTRACE_MODE_FSCREDS.
Jeff Xu Dec. 15, 2022, 8:34 p.m. UTC | #2
Hi Mickaël
Thanks for reviewing.

On Thu, Dec 15, 2022 at 10:34 AM Mickaël Salaün <mic@digikod.net> wrote:
>
> This is much better! We can tailor a bit more the tests though.
>
> On 13/12/2022 19:58, jeffxu@chromium.org wrote:
> > From: Jeff Xu <jeffxu@google.com>
> >
> > Add check for yama setting for ptrace_test.
> >
> > Signed-off-by: Jeff Xu <jeffxu@google.com>
> > ---
> >   .../testing/selftests/landlock/ptrace_test.c  | 34 +++++++++++++++++++
> >   1 file changed, 34 insertions(+)
> >
> > diff --git a/tools/testing/selftests/landlock/ptrace_test.c b/tools/testing/selftests/landlock/ptrace_test.c
> > index c28ef98ff3ac..8565a25a9587 100644
> > --- a/tools/testing/selftests/landlock/ptrace_test.c
> > +++ b/tools/testing/selftests/landlock/ptrace_test.c
> > @@ -60,6 +60,24 @@ static int test_ptrace_read(const pid_t pid)
> >       return 0;
> >   }
> >
> > +static int get_ptrace_scope(void)
>
> Please rename to get_yama_ptrace_scope().
>
Done.

> > +{
> > +     int ret = -1;
> > +     char buf[2];
> > +     int fd = open("/proc/sys/kernel/yama/ptrace_scope", O_RDONLY);
> > +
> > +     if (fd < 0)
> > +             return 0;
> > +
> > +     if (read(fd, &buf, 1) < 0)
> > +             return -1;
> > +
> > +     buf[1] = '\0';
>
> You can replace that with `char buf[2] = {};`
>
Done.
The Compiler seems to be getting a lot smarter :) Thanks.

>
> > +     ret = atoi(buf);
> > +     close(fd);
> > +     return ret;
> > +}
> > +
> >   /* clang-format off */
> >   FIXTURE(hierarchy) {};
> >   /* clang-format on */
> > @@ -69,6 +87,7 @@ FIXTURE_VARIANT(hierarchy)
> >       const bool domain_both;
> >       const bool domain_parent;
> >       const bool domain_child;
> > +     const int  yama_value;
>
> Please rename to yama_ptrace_scope_max and remove the extra space.
>
why _max ?  yama_ptrace_scope_current is more proporate ?
FYI: This is the current sysctl setting.

> >   };
> >
> >   /*
> > @@ -93,6 +112,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_without_domain) {
> >       .domain_both = false,
> >       .domain_parent = false,
> >       .domain_child = false,
> > +     .yama_value = 0,
> >   };
> >
> >   /*
> > @@ -110,6 +130,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_with_one_domain) {
> >       .domain_both = false,
> >       .domain_parent = false,
> >       .domain_child = true,
> > +     .yama_value = 1,
> >   };
> >
> >   /*
> > @@ -126,6 +147,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_parent_domain) {
> >       .domain_both = false,
> >       .domain_parent = true,
> >       .domain_child = false,
> > +     .yama_value = 0,
> >   };
> >
> >   /*
> > @@ -143,6 +165,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_sibling_domain) {
> >       .domain_both = false,
> >       .domain_parent = true,
> >       .domain_child = true,
> > +     .yama_value = 2,
> >   };
> >
> >   /*
> > @@ -160,6 +183,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_sibling_domain) {
> >       .domain_both = true,
> >       .domain_parent = false,
> >       .domain_child = false,
> > +     .yama_value = 0,
> >   };
> >
> >   /*
> > @@ -178,6 +202,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_with_nested_domain) {
> >       .domain_both = true,
> >       .domain_parent = false,
> >       .domain_child = true,
> > +     .yama_value = 1,
> >   };
> >
> >   /*
> > @@ -196,6 +221,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_nested_and_parent_domain) {
> >       .domain_both = true,
> >       .domain_parent = true,
> >       .domain_child = false,
> > +     .yama_value = 0,
> >   };
> >
> >   /*
> > @@ -216,6 +242,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_forked_domain) {
> >       .domain_both = true,
> >       .domain_parent = true,
> >       .domain_child = true,
> > +     .yama_value = 2,
> >   };
> >
> >   FIXTURE_SETUP(hierarchy)
> > @@ -232,9 +259,16 @@ TEST_F(hierarchy, trace)
> >       pid_t child, parent;
> >       int status, err_proc_read;
> >       int pipe_child[2], pipe_parent[2];
> > +     int yama;
>
> Please rename to yama_ptrace_scope.
>
Done.


>
> >       char buf_parent;
> >       long ret;
> >
> > +     yama = get_ptrace_scope();
> > +     ASSERT_LE(0, yama);
> > +
> > +     if (variant->yama_value < yama)
>
> if (yama_ptrace_scope >= 3)
>
> > +             SKIP(return, "unsupported yama value %d", yama);
>
> "Yama forbids any ptrace use (scope 3)"
>
>
why comparing with  3?  the test will  skip particular hierarchy,
according to current
sysctl yama_ptrace setting.

For example: when kernel.yama.ptrace_scope = 1 the result will be like:
localhost /usr/local/bin # ./ptrace_test
TAP version 13
1..8
# Starting 8 tests from 9 test cases.
#  RUN           hierarchy.allow_without_domain.trace ...
#      SKIP      unsupported yama value 1
#            OK  hierarchy.allow_without_domain.trace
ok 1 # SKIP unsupported yama value 1
#  RUN           hierarchy.allow_with_one_domain.trace ...
#            OK  hierarchy.allow_with_one_domain.trace
ok 2 hierarchy.allow_with_one_domain.trace
#  RUN           hierarchy.deny_with_parent_domain.trace ...
#      SKIP      unsupported yama value 1
#            OK  hierarchy.deny_with_parent_domain.trace
ok 3 # SKIP unsupported yama value 1
#  RUN           hierarchy.deny_with_sibling_domain.trace ...
#            OK  hierarchy.deny_with_sibling_domain.trace
ok 4 hierarchy.deny_with_sibling_domain.trace
#  RUN           hierarchy.allow_sibling_domain.trace ...
#      SKIP      unsupported yama value 1
#            OK  hierarchy.allow_sibling_domain.trace
ok 5 # SKIP unsupported yama value 1
#  RUN           hierarchy.allow_with_nested_domain.trace ...
#            OK  hierarchy.allow_with_nested_domain.trace
ok 6 hierarchy.allow_with_nested_domain.trace
#  RUN           hierarchy.deny_with_nested_and_parent_domain.trace ...
#      SKIP      unsupported yama value 1
#            OK  hierarchy.deny_with_nested_and_parent_domain.trace
ok 7 # SKIP unsupported yama value 1
#  RUN           hierarchy.deny_with_forked_domain.trace ...
#            OK  hierarchy.deny_with_forked_domain.trace
ok 8 hierarchy.deny_with_forked_domain.trace
# PASSED: 8 / 8 tests passed.
# Totals: pass:4 fail:0 xfail:0 xpass:0 skip:4 error:0

when yama.ptrace_scope is 2:
localhost /usr/local/bin # sysctl kernel.yama.ptrace_scope=2
kernel.yama.ptrace_scope = 2
localhost /usr/local/bin # ./ptrace_test
TAP version 13
1..8
# Starting 8 tests from 9 test cases.
#  RUN           hierarchy.allow_without_domain.trace ...
#      SKIP      unsupported yama value 2
#            OK  hierarchy.allow_without_domain.trace
ok 1 # SKIP unsupported yama value 2
#  RUN           hierarchy.allow_with_one_domain.trace ...
#      SKIP      unsupported yama value 2
#            OK  hierarchy.allow_with_one_domain.trace
ok 2 # SKIP unsupported yama value 2
#  RUN           hierarchy.deny_with_parent_domain.trace ...
#      SKIP      unsupported yama value 2
#            OK  hierarchy.deny_with_parent_domain.trace
ok 3 # SKIP unsupported yama value 2
#  RUN           hierarchy.deny_with_sibling_domain.trace ...
#            OK  hierarchy.deny_with_sibling_domain.trace
ok 4 hierarchy.deny_with_sibling_domain.trace
#  RUN           hierarchy.allow_sibling_domain.trace ...
#      SKIP      unsupported yama value 2
#            OK  hierarchy.allow_sibling_domain.trace
ok 5 # SKIP unsupported yama value 2
#  RUN           hierarchy.allow_with_nested_domain.trace ...
#      SKIP      unsupported yama value 2
#            OK  hierarchy.allow_with_nested_domain.trace
ok 6 # SKIP unsupported yama value 2
#  RUN           hierarchy.deny_with_nested_and_parent_domain.trace ...
#      SKIP      unsupported yama value 2
#            OK  hierarchy.deny_with_nested_and_parent_domain.trace
ok 7 # SKIP unsupported yama value 2
#  RUN           hierarchy.deny_with_forked_domain.trace ...
#            OK  hierarchy.deny_with_forked_domain.trace
ok 8 hierarchy.deny_with_forked_domain.trace
# PASSED: 8 / 8 tests passed.
# Totals: pass:2 fail:0 xfail:0 xpass:0 skip:6 error:0

> This check skips the whole test, whereas the issues with Yama are about:
> - a child process tracing its parent;
> - the PTRACE_TRACEME case.
>
> I think the main remaining parts to change is the `if
> (variant->domain_*` checks to extend with the yama_ptrace_scope_max check.
>
> However, it is useful to highlight that a test didn't fully cover
> Landlock checks. I think the best approach is to call SKIP() at the end
> of TEST_F(hierarchy, trace) if yama_ptrace_scope >= 1 . This way, we
> test as much as possible (Landlock and Yama) and we mark the "tampered"
> tests as skipped.
>
I believe the test case should not have a lot of branches and logic
(if/else), which makes
the test case more complex and harder to read.  By that reason, SKIP()
is better at beginning
of the testcase.

Another reason is resource cleanup.  When SKIP() is not at the
beginning of tests,
the cleanup logic can get much more complicated because there are more
combinations of resource cleanup to
to be dealt with, after SKIP().

Therefore I do not believe in "tests as much as possible" in a single
test, I would rather have a
dedicated test for the situation.

Thoughts ?

>
> > +
> >       /*
> >        * Removes all effective and permitted capabilities to not interfere
> >        * with cap_ptrace_access_check() in case of PTRACE_MODE_FSCREDS.
Jeff Xu Dec. 15, 2022, 8:42 p.m. UTC | #3
On Thu, Dec 15, 2022 at 12:34 PM Jeff Xu <jeffxu@google.com> wrote:
>
> Hi Mickaël
> Thanks for reviewing.
>
> On Thu, Dec 15, 2022 at 10:34 AM Mickaël Salaün <mic@digikod.net> wrote:
> >
> > This is much better! We can tailor a bit more the tests though.
> >
> > On 13/12/2022 19:58, jeffxu@chromium.org wrote:
> > > From: Jeff Xu <jeffxu@google.com>
> > >
> > > Add check for yama setting for ptrace_test.
> > >
> > > Signed-off-by: Jeff Xu <jeffxu@google.com>
> > > ---
> > >   .../testing/selftests/landlock/ptrace_test.c  | 34 +++++++++++++++++++
> > >   1 file changed, 34 insertions(+)
> > >
> > > diff --git a/tools/testing/selftests/landlock/ptrace_test.c b/tools/testing/selftests/landlock/ptrace_test.c
> > > index c28ef98ff3ac..8565a25a9587 100644
> > > --- a/tools/testing/selftests/landlock/ptrace_test.c
> > > +++ b/tools/testing/selftests/landlock/ptrace_test.c
> > > @@ -60,6 +60,24 @@ static int test_ptrace_read(const pid_t pid)
> > >       return 0;
> > >   }
> > >
> > > +static int get_ptrace_scope(void)
> >
> > Please rename to get_yama_ptrace_scope().
> >
> Done.
>
> > > +{
> > > +     int ret = -1;
> > > +     char buf[2];
> > > +     int fd = open("/proc/sys/kernel/yama/ptrace_scope", O_RDONLY);
> > > +
> > > +     if (fd < 0)
> > > +             return 0;
> > > +
> > > +     if (read(fd, &buf, 1) < 0)
> > > +             return -1;
> > > +
> > > +     buf[1] = '\0';
> >
> > You can replace that with `char buf[2] = {};`
> >
> Done.
> The Compiler seems to be getting a lot smarter :) Thanks.
>
> >
> > > +     ret = atoi(buf);
> > > +     close(fd);
> > > +     return ret;
> > > +}
> > > +
> > >   /* clang-format off */
> > >   FIXTURE(hierarchy) {};
> > >   /* clang-format on */
> > > @@ -69,6 +87,7 @@ FIXTURE_VARIANT(hierarchy)
> > >       const bool domain_both;
> > >       const bool domain_parent;
> > >       const bool domain_child;
> > > +     const int  yama_value;
> >
> > Please rename to yama_ptrace_scope_max and remove the extra space.
> >
> why _max ?  yama_ptrace_scope_current is more proporate ?
> FYI: This is the current sysctl setting.
>
Sorry, I will correct myself. This is max supported by the variant,
not the current sysctl setting.
I will change it to :
yama_ptrace_scope_max_supported

> > >   };
> > >
> > >   /*
> > > @@ -93,6 +112,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_without_domain) {
> > >       .domain_both = false,
> > >       .domain_parent = false,
> > >       .domain_child = false,
> > > +     .yama_value = 0,
> > >   };
> > >
> > >   /*
> > > @@ -110,6 +130,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_with_one_domain) {
> > >       .domain_both = false,
> > >       .domain_parent = false,
> > >       .domain_child = true,
> > > +     .yama_value = 1,
> > >   };
> > >
> > >   /*
> > > @@ -126,6 +147,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_parent_domain) {
> > >       .domain_both = false,
> > >       .domain_parent = true,
> > >       .domain_child = false,
> > > +     .yama_value = 0,
> > >   };
> > >
> > >   /*
> > > @@ -143,6 +165,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_sibling_domain) {
> > >       .domain_both = false,
> > >       .domain_parent = true,
> > >       .domain_child = true,
> > > +     .yama_value = 2,
> > >   };
> > >
> > >   /*
> > > @@ -160,6 +183,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_sibling_domain) {
> > >       .domain_both = true,
> > >       .domain_parent = false,
> > >       .domain_child = false,
> > > +     .yama_value = 0,
> > >   };
> > >
> > >   /*
> > > @@ -178,6 +202,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_with_nested_domain) {
> > >       .domain_both = true,
> > >       .domain_parent = false,
> > >       .domain_child = true,
> > > +     .yama_value = 1,
> > >   };
> > >
> > >   /*
> > > @@ -196,6 +221,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_nested_and_parent_domain) {
> > >       .domain_both = true,
> > >       .domain_parent = true,
> > >       .domain_child = false,
> > > +     .yama_value = 0,
> > >   };
> > >
> > >   /*
> > > @@ -216,6 +242,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_forked_domain) {
> > >       .domain_both = true,
> > >       .domain_parent = true,
> > >       .domain_child = true,
> > > +     .yama_value = 2,
> > >   };
> > >
> > >   FIXTURE_SETUP(hierarchy)
> > > @@ -232,9 +259,16 @@ TEST_F(hierarchy, trace)
> > >       pid_t child, parent;
> > >       int status, err_proc_read;
> > >       int pipe_child[2], pipe_parent[2];
> > > +     int yama;
> >
> > Please rename to yama_ptrace_scope.
> >
> Done.
>
>
> >
> > >       char buf_parent;
> > >       long ret;
> > >
> > > +     yama = get_ptrace_scope();
> > > +     ASSERT_LE(0, yama);
> > > +
> > > +     if (variant->yama_value < yama)
> >
> > if (yama_ptrace_scope >= 3)
> >
> > > +             SKIP(return, "unsupported yama value %d", yama);
> >
> > "Yama forbids any ptrace use (scope 3)"
> >
> >
> why comparing with  3?  the test will  skip particular hierarchy,
> according to current
> sysctl yama_ptrace setting.
>
> For example: when kernel.yama.ptrace_scope = 1 the result will be like:
> localhost /usr/local/bin # ./ptrace_test
> TAP version 13
> 1..8
> # Starting 8 tests from 9 test cases.
> #  RUN           hierarchy.allow_without_domain.trace ...
> #      SKIP      unsupported yama value 1
> #            OK  hierarchy.allow_without_domain.trace
> ok 1 # SKIP unsupported yama value 1
> #  RUN           hierarchy.allow_with_one_domain.trace ...
> #            OK  hierarchy.allow_with_one_domain.trace
> ok 2 hierarchy.allow_with_one_domain.trace
> #  RUN           hierarchy.deny_with_parent_domain.trace ...
> #      SKIP      unsupported yama value 1
> #            OK  hierarchy.deny_with_parent_domain.trace
> ok 3 # SKIP unsupported yama value 1
> #  RUN           hierarchy.deny_with_sibling_domain.trace ...
> #            OK  hierarchy.deny_with_sibling_domain.trace
> ok 4 hierarchy.deny_with_sibling_domain.trace
> #  RUN           hierarchy.allow_sibling_domain.trace ...
> #      SKIP      unsupported yama value 1
> #            OK  hierarchy.allow_sibling_domain.trace
> ok 5 # SKIP unsupported yama value 1
> #  RUN           hierarchy.allow_with_nested_domain.trace ...
> #            OK  hierarchy.allow_with_nested_domain.trace
> ok 6 hierarchy.allow_with_nested_domain.trace
> #  RUN           hierarchy.deny_with_nested_and_parent_domain.trace ...
> #      SKIP      unsupported yama value 1
> #            OK  hierarchy.deny_with_nested_and_parent_domain.trace
> ok 7 # SKIP unsupported yama value 1
> #  RUN           hierarchy.deny_with_forked_domain.trace ...
> #            OK  hierarchy.deny_with_forked_domain.trace
> ok 8 hierarchy.deny_with_forked_domain.trace
> # PASSED: 8 / 8 tests passed.
> # Totals: pass:4 fail:0 xfail:0 xpass:0 skip:4 error:0
>
> when yama.ptrace_scope is 2:
> localhost /usr/local/bin # sysctl kernel.yama.ptrace_scope=2
> kernel.yama.ptrace_scope = 2
> localhost /usr/local/bin # ./ptrace_test
> TAP version 13
> 1..8
> # Starting 8 tests from 9 test cases.
> #  RUN           hierarchy.allow_without_domain.trace ...
> #      SKIP      unsupported yama value 2
> #            OK  hierarchy.allow_without_domain.trace
> ok 1 # SKIP unsupported yama value 2
> #  RUN           hierarchy.allow_with_one_domain.trace ...
> #      SKIP      unsupported yama value 2
> #            OK  hierarchy.allow_with_one_domain.trace
> ok 2 # SKIP unsupported yama value 2
> #  RUN           hierarchy.deny_with_parent_domain.trace ...
> #      SKIP      unsupported yama value 2
> #            OK  hierarchy.deny_with_parent_domain.trace
> ok 3 # SKIP unsupported yama value 2
> #  RUN           hierarchy.deny_with_sibling_domain.trace ...
> #            OK  hierarchy.deny_with_sibling_domain.trace
> ok 4 hierarchy.deny_with_sibling_domain.trace
> #  RUN           hierarchy.allow_sibling_domain.trace ...
> #      SKIP      unsupported yama value 2
> #            OK  hierarchy.allow_sibling_domain.trace
> ok 5 # SKIP unsupported yama value 2
> #  RUN           hierarchy.allow_with_nested_domain.trace ...
> #      SKIP      unsupported yama value 2
> #            OK  hierarchy.allow_with_nested_domain.trace
> ok 6 # SKIP unsupported yama value 2
> #  RUN           hierarchy.deny_with_nested_and_parent_domain.trace ...
> #      SKIP      unsupported yama value 2
> #            OK  hierarchy.deny_with_nested_and_parent_domain.trace
> ok 7 # SKIP unsupported yama value 2
> #  RUN           hierarchy.deny_with_forked_domain.trace ...
> #            OK  hierarchy.deny_with_forked_domain.trace
> ok 8 hierarchy.deny_with_forked_domain.trace
> # PASSED: 8 / 8 tests passed.
> # Totals: pass:2 fail:0 xfail:0 xpass:0 skip:6 error:0
>
> > This check skips the whole test, whereas the issues with Yama are about:
> > - a child process tracing its parent;
> > - the PTRACE_TRACEME case.
> >
> > I think the main remaining parts to change is the `if
> > (variant->domain_*` checks to extend with the yama_ptrace_scope_max check.
> >
> > However, it is useful to highlight that a test didn't fully cover
> > Landlock checks. I think the best approach is to call SKIP() at the end
> > of TEST_F(hierarchy, trace) if yama_ptrace_scope >= 1 . This way, we
> > test as much as possible (Landlock and Yama) and we mark the "tampered"
> > tests as skipped.
> >
> I believe the test case should not have a lot of branches and logic
> (if/else), which makes
> the test case more complex and harder to read.  By that reason, SKIP()
> is better at beginning
> of the testcase.
>
> Another reason is resource cleanup.  When SKIP() is not at the
> beginning of tests,
> the cleanup logic can get much more complicated because there are more
> combinations of resource cleanup to
> to be dealt with, after SKIP().
>
> Therefore I do not believe in "tests as much as possible" in a single
> test, I would rather have a
> dedicated test for the situation.
>
> Thoughts ?
>
> >
> > > +
> > >       /*
> > >        * Removes all effective and permitted capabilities to not interfere
> > >        * with cap_ptrace_access_check() in case of PTRACE_MODE_FSCREDS.
Mickaël Salaün Dec. 16, 2022, 10:15 a.m. UTC | #4
On 15/12/2022 21:34, Jeff Xu wrote:
> Hi Mickaël
> Thanks for reviewing.
> 
> On Thu, Dec 15, 2022 at 10:34 AM Mickaël Salaün <mic@digikod.net> wrote:
>>
>> This is much better! We can tailor a bit more the tests though.
>>
>> On 13/12/2022 19:58, jeffxu@chromium.org wrote:
>>> From: Jeff Xu <jeffxu@google.com>
>>>
>>> Add check for yama setting for ptrace_test.
>>>
>>> Signed-off-by: Jeff Xu <jeffxu@google.com>
>>> ---
>>>    .../testing/selftests/landlock/ptrace_test.c  | 34 +++++++++++++++++++
>>>    1 file changed, 34 insertions(+)
>>>
>>> diff --git a/tools/testing/selftests/landlock/ptrace_test.c b/tools/testing/selftests/landlock/ptrace_test.c
>>> index c28ef98ff3ac..8565a25a9587 100644
>>> --- a/tools/testing/selftests/landlock/ptrace_test.c
>>> +++ b/tools/testing/selftests/landlock/ptrace_test.c
>>> @@ -60,6 +60,24 @@ static int test_ptrace_read(const pid_t pid)
>>>        return 0;
>>>    }
>>>
>>> +static int get_ptrace_scope(void)
>>
>> Please rename to get_yama_ptrace_scope().
>>
> Done.
> 
>>> +{
>>> +     int ret = -1;
>>> +     char buf[2];
>>> +     int fd = open("/proc/sys/kernel/yama/ptrace_scope", O_RDONLY);
>>> +
>>> +     if (fd < 0)
>>> +             return 0;
>>> +
>>> +     if (read(fd, &buf, 1) < 0)
>>> +             return -1;
>>> +
>>> +     buf[1] = '\0';
>>
>> You can replace that with `char buf[2] = {};`
>>
> Done.
> The Compiler seems to be getting a lot smarter :) Thanks.
> 
>>
>>> +     ret = atoi(buf);
>>> +     close(fd);
>>> +     return ret;
>>> +}
>>> +
>>>    /* clang-format off */
>>>    FIXTURE(hierarchy) {};
>>>    /* clang-format on */
>>> @@ -69,6 +87,7 @@ FIXTURE_VARIANT(hierarchy)
>>>        const bool domain_both;
>>>        const bool domain_parent;
>>>        const bool domain_child;
>>> +     const int  yama_value;
>>
>> Please rename to yama_ptrace_scope_max and remove the extra space.
>>
> why _max ?  yama_ptrace_scope_current is more proporate ?
> FYI: This is the current sysctl setting.

In response to your other email, yama_ptrace_scope_max_supported looks 
good too.

> 
>>>    };
>>>
>>>    /*
>>> @@ -93,6 +112,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_without_domain) {
>>>        .domain_both = false,
>>>        .domain_parent = false,
>>>        .domain_child = false,
>>> +     .yama_value = 0,
>>>    };
>>>
>>>    /*
>>> @@ -110,6 +130,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_with_one_domain) {
>>>        .domain_both = false,
>>>        .domain_parent = false,
>>>        .domain_child = true,
>>> +     .yama_value = 1,
>>>    };
>>>
>>>    /*
>>> @@ -126,6 +147,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_parent_domain) {
>>>        .domain_both = false,
>>>        .domain_parent = true,
>>>        .domain_child = false,
>>> +     .yama_value = 0,
>>>    };
>>>
>>>    /*
>>> @@ -143,6 +165,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_sibling_domain) {
>>>        .domain_both = false,
>>>        .domain_parent = true,
>>>        .domain_child = true,
>>> +     .yama_value = 2,
>>>    };
>>>
>>>    /*
>>> @@ -160,6 +183,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_sibling_domain) {
>>>        .domain_both = true,
>>>        .domain_parent = false,
>>>        .domain_child = false,
>>> +     .yama_value = 0,
>>>    };
>>>
>>>    /*
>>> @@ -178,6 +202,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_with_nested_domain) {
>>>        .domain_both = true,
>>>        .domain_parent = false,
>>>        .domain_child = true,
>>> +     .yama_value = 1,
>>>    };
>>>
>>>    /*
>>> @@ -196,6 +221,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_nested_and_parent_domain) {
>>>        .domain_both = true,
>>>        .domain_parent = true,
>>>        .domain_child = false,
>>> +     .yama_value = 0,
>>>    };
>>>
>>>    /*
>>> @@ -216,6 +242,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_forked_domain) {
>>>        .domain_both = true,
>>>        .domain_parent = true,
>>>        .domain_child = true,
>>> +     .yama_value = 2,
>>>    };
>>>
>>>    FIXTURE_SETUP(hierarchy)
>>> @@ -232,9 +259,16 @@ TEST_F(hierarchy, trace)
>>>        pid_t child, parent;
>>>        int status, err_proc_read;
>>>        int pipe_child[2], pipe_parent[2];
>>> +     int yama;
>>
>> Please rename to yama_ptrace_scope.
>>
> Done.
> 
> 
>>
>>>        char buf_parent;
>>>        long ret;
>>>
>>> +     yama = get_ptrace_scope();
>>> +     ASSERT_LE(0, yama);
>>> +
>>> +     if (variant->yama_value < yama)
>>
>> if (yama_ptrace_scope >= 3)
>>
>>> +             SKIP(return, "unsupported yama value %d", yama);
>>
>> "Yama forbids any ptrace use (scope 3)"
>>
>>
> why comparing with  3?  the test will  skip particular hierarchy,
> according to current
> sysctl yama_ptrace setting.

The idea is to run the tests as much as possible, but in the case of a 
scope of 3, any ptrace is denied. However, it would indeed be better to 
integrate this third value in the following `if (variant->domain_*` 
checks, like for the other scopes.


> 
> For example: when kernel.yama.ptrace_scope = 1 the result will be like:
> localhost /usr/local/bin # ./ptrace_test
> TAP version 13
> 1..8
> # Starting 8 tests from 9 test cases.
> #  RUN           hierarchy.allow_without_domain.trace ...
> #      SKIP      unsupported yama value 1
> #            OK  hierarchy.allow_without_domain.trace
> ok 1 # SKIP unsupported yama value 1
> #  RUN           hierarchy.allow_with_one_domain.trace ...
> #            OK  hierarchy.allow_with_one_domain.trace
> ok 2 hierarchy.allow_with_one_domain.trace
> #  RUN           hierarchy.deny_with_parent_domain.trace ...
> #      SKIP      unsupported yama value 1
> #            OK  hierarchy.deny_with_parent_domain.trace
> ok 3 # SKIP unsupported yama value 1
> #  RUN           hierarchy.deny_with_sibling_domain.trace ...
> #            OK  hierarchy.deny_with_sibling_domain.trace
> ok 4 hierarchy.deny_with_sibling_domain.trace
> #  RUN           hierarchy.allow_sibling_domain.trace ...
> #      SKIP      unsupported yama value 1
> #            OK  hierarchy.allow_sibling_domain.trace
> ok 5 # SKIP unsupported yama value 1
> #  RUN           hierarchy.allow_with_nested_domain.trace ...
> #            OK  hierarchy.allow_with_nested_domain.trace
> ok 6 hierarchy.allow_with_nested_domain.trace
> #  RUN           hierarchy.deny_with_nested_and_parent_domain.trace ...
> #      SKIP      unsupported yama value 1
> #            OK  hierarchy.deny_with_nested_and_parent_domain.trace
> ok 7 # SKIP unsupported yama value 1
> #  RUN           hierarchy.deny_with_forked_domain.trace ...
> #            OK  hierarchy.deny_with_forked_domain.trace
> ok 8 hierarchy.deny_with_forked_domain.trace
> # PASSED: 8 / 8 tests passed.
> # Totals: pass:4 fail:0 xfail:0 xpass:0 skip:4 error:0
> 
> when yama.ptrace_scope is 2:
> localhost /usr/local/bin # sysctl kernel.yama.ptrace_scope=2
> kernel.yama.ptrace_scope = 2
> localhost /usr/local/bin # ./ptrace_test
> TAP version 13
> 1..8
> # Starting 8 tests from 9 test cases.
> #  RUN           hierarchy.allow_without_domain.trace ...
> #      SKIP      unsupported yama value 2
> #            OK  hierarchy.allow_without_domain.trace
> ok 1 # SKIP unsupported yama value 2
> #  RUN           hierarchy.allow_with_one_domain.trace ...
> #      SKIP      unsupported yama value 2
> #            OK  hierarchy.allow_with_one_domain.trace
> ok 2 # SKIP unsupported yama value 2
> #  RUN           hierarchy.deny_with_parent_domain.trace ...
> #      SKIP      unsupported yama value 2
> #            OK  hierarchy.deny_with_parent_domain.trace
> ok 3 # SKIP unsupported yama value 2
> #  RUN           hierarchy.deny_with_sibling_domain.trace ...
> #            OK  hierarchy.deny_with_sibling_domain.trace
> ok 4 hierarchy.deny_with_sibling_domain.trace
> #  RUN           hierarchy.allow_sibling_domain.trace ...
> #      SKIP      unsupported yama value 2
> #            OK  hierarchy.allow_sibling_domain.trace
> ok 5 # SKIP unsupported yama value 2
> #  RUN           hierarchy.allow_with_nested_domain.trace ...
> #      SKIP      unsupported yama value 2
> #            OK  hierarchy.allow_with_nested_domain.trace
> ok 6 # SKIP unsupported yama value 2
> #  RUN           hierarchy.deny_with_nested_and_parent_domain.trace ...
> #      SKIP      unsupported yama value 2
> #            OK  hierarchy.deny_with_nested_and_parent_domain.trace
> ok 7 # SKIP unsupported yama value 2
> #  RUN           hierarchy.deny_with_forked_domain.trace ...
> #            OK  hierarchy.deny_with_forked_domain.trace
> ok 8 hierarchy.deny_with_forked_domain.trace
> # PASSED: 8 / 8 tests passed.
> # Totals: pass:2 fail:0 xfail:0 xpass:0 skip:6 error:0
> 
>> This check skips the whole test, whereas the issues with Yama are about:
>> - a child process tracing its parent;
>> - the PTRACE_TRACEME case.
>>
>> I think the main remaining parts to change is the `if
>> (variant->domain_*` checks to extend with the yama_ptrace_scope_max check.
>>
>> However, it is useful to highlight that a test didn't fully cover
>> Landlock checks. I think the best approach is to call SKIP() at the end
>> of TEST_F(hierarchy, trace) if yama_ptrace_scope >= 1 . This way, we
>> test as much as possible (Landlock and Yama) and we mark the "tampered"
>> tests as skipped.
>>
> I believe the test case should not have a lot of branches and logic
> (if/else), which makes
> the test case more complex and harder to read.  By that reason, SKIP()
> is better at beginning
> of the testcase.

I agree in a general case, but here all the branches already exist to 
test all possible Landlock combinations. Adding Yama's ptrace scope will 
only update the existing branch conditions.


> 
> Another reason is resource cleanup.  When SKIP() is not at the
> beginning of tests,
> the cleanup logic can get much more complicated because there are more
> combinations of resource cleanup to
> to be dealt with, after SKIP().

All the logic for resource cleanup is already in place.

> 
> Therefore I do not believe in "tests as much as possible" in a single
> test, I would rather have a
> dedicated test for the situation.

The current test code already covers all possible combinations, so it is 
just a matter of extending the branch conditions. You can update these 
checks using dedicated booleans:
- can_trace_child = !variant->domain_parent && (yama_ptrace_scope < 2);
- can_trace_parent = !variant->domain_child && (yama_ptrace_scope < 1);

…and at the end of all the hierarchy.trace tests add:
if (yama_ptrace_scope > 0)
	SKIP(return, "Incomplete tests due to Yama restrictions (ptrace_scope: 
%d)", yama_ptrace_scope);
Jeff Xu Dec. 16, 2022, 3:18 p.m. UTC | #5
On Fri, Dec 16, 2022 at 2:15 AM Mickaël Salaün <mic@digikod.net> wrote:
>
>
> On 15/12/2022 21:34, Jeff Xu wrote:
> > Hi Mickaël
> > Thanks for reviewing.
> >
> > On Thu, Dec 15, 2022 at 10:34 AM Mickaël Salaün <mic@digikod.net> wrote:
> >>
> >> This is much better! We can tailor a bit more the tests though.
> >>
> >> On 13/12/2022 19:58, jeffxu@chromium.org wrote:
> >>> From: Jeff Xu <jeffxu@google.com>
> >>>
> >>> Add check for yama setting for ptrace_test.
> >>>
> >>> Signed-off-by: Jeff Xu <jeffxu@google.com>
> >>> ---
> >>>    .../testing/selftests/landlock/ptrace_test.c  | 34 +++++++++++++++++++
> >>>    1 file changed, 34 insertions(+)
> >>>
> >>> diff --git a/tools/testing/selftests/landlock/ptrace_test.c b/tools/testing/selftests/landlock/ptrace_test.c
> >>> index c28ef98ff3ac..8565a25a9587 100644
> >>> --- a/tools/testing/selftests/landlock/ptrace_test.c
> >>> +++ b/tools/testing/selftests/landlock/ptrace_test.c
> >>> @@ -60,6 +60,24 @@ static int test_ptrace_read(const pid_t pid)
> >>>        return 0;
> >>>    }
> >>>
> >>> +static int get_ptrace_scope(void)
> >>
> >> Please rename to get_yama_ptrace_scope().
> >>
> > Done.
> >
> >>> +{
> >>> +     int ret = -1;
> >>> +     char buf[2];
> >>> +     int fd = open("/proc/sys/kernel/yama/ptrace_scope", O_RDONLY);
> >>> +
> >>> +     if (fd < 0)
> >>> +             return 0;
> >>> +
> >>> +     if (read(fd, &buf, 1) < 0)
> >>> +             return -1;
> >>> +
> >>> +     buf[1] = '\0';
> >>
> >> You can replace that with `char buf[2] = {};`
> >>
> > Done.
> > The Compiler seems to be getting a lot smarter :) Thanks.
> >
> >>
> >>> +     ret = atoi(buf);
> >>> +     close(fd);
> >>> +     return ret;
> >>> +}
> >>> +
> >>>    /* clang-format off */
> >>>    FIXTURE(hierarchy) {};
> >>>    /* clang-format on */
> >>> @@ -69,6 +87,7 @@ FIXTURE_VARIANT(hierarchy)
> >>>        const bool domain_both;
> >>>        const bool domain_parent;
> >>>        const bool domain_child;
> >>> +     const int  yama_value;
> >>
> >> Please rename to yama_ptrace_scope_max and remove the extra space.
> >>
> > why _max ?  yama_ptrace_scope_current is more proporate ?
> > FYI: This is the current sysctl setting.
>
> In response to your other email, yama_ptrace_scope_max_supported looks
> good too.
>
> >
> >>>    };
> >>>
> >>>    /*
> >>> @@ -93,6 +112,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_without_domain) {
> >>>        .domain_both = false,
> >>>        .domain_parent = false,
> >>>        .domain_child = false,
> >>> +     .yama_value = 0,
> >>>    };
> >>>
> >>>    /*
> >>> @@ -110,6 +130,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_with_one_domain) {
> >>>        .domain_both = false,
> >>>        .domain_parent = false,
> >>>        .domain_child = true,
> >>> +     .yama_value = 1,
> >>>    };
> >>>
> >>>    /*
> >>> @@ -126,6 +147,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_parent_domain) {
> >>>        .domain_both = false,
> >>>        .domain_parent = true,
> >>>        .domain_child = false,
> >>> +     .yama_value = 0,
> >>>    };
> >>>
> >>>    /*
> >>> @@ -143,6 +165,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_sibling_domain) {
> >>>        .domain_both = false,
> >>>        .domain_parent = true,
> >>>        .domain_child = true,
> >>> +     .yama_value = 2,
> >>>    };
> >>>
> >>>    /*
> >>> @@ -160,6 +183,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_sibling_domain) {
> >>>        .domain_both = true,
> >>>        .domain_parent = false,
> >>>        .domain_child = false,
> >>> +     .yama_value = 0,
> >>>    };
> >>>
> >>>    /*
> >>> @@ -178,6 +202,7 @@ FIXTURE_VARIANT_ADD(hierarchy, allow_with_nested_domain) {
> >>>        .domain_both = true,
> >>>        .domain_parent = false,
> >>>        .domain_child = true,
> >>> +     .yama_value = 1,
> >>>    };
> >>>
> >>>    /*
> >>> @@ -196,6 +221,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_nested_and_parent_domain) {
> >>>        .domain_both = true,
> >>>        .domain_parent = true,
> >>>        .domain_child = false,
> >>> +     .yama_value = 0,
> >>>    };
> >>>
> >>>    /*
> >>> @@ -216,6 +242,7 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_forked_domain) {
> >>>        .domain_both = true,
> >>>        .domain_parent = true,
> >>>        .domain_child = true,
> >>> +     .yama_value = 2,
> >>>    };
> >>>
> >>>    FIXTURE_SETUP(hierarchy)
> >>> @@ -232,9 +259,16 @@ TEST_F(hierarchy, trace)
> >>>        pid_t child, parent;
> >>>        int status, err_proc_read;
> >>>        int pipe_child[2], pipe_parent[2];
> >>> +     int yama;
> >>
> >> Please rename to yama_ptrace_scope.
> >>
> > Done.
> >
> >
> >>
> >>>        char buf_parent;
> >>>        long ret;
> >>>
> >>> +     yama = get_ptrace_scope();
> >>> +     ASSERT_LE(0, yama);
> >>> +
> >>> +     if (variant->yama_value < yama)
> >>
> >> if (yama_ptrace_scope >= 3)
> >>
> >>> +             SKIP(return, "unsupported yama value %d", yama);
> >>
> >> "Yama forbids any ptrace use (scope 3)"
> >>
> >>
> > why comparing with  3?  the test will  skip particular hierarchy,
> > according to current
> > sysctl yama_ptrace setting.
>
> The idea is to run the tests as much as possible, but in the case of a
> scope of 3, any ptrace is denied. However, it would indeed be better to
> integrate this third value in the following `if (variant->domain_*`
> checks, like for the other scopes.
>
>
> >
> > For example: when kernel.yama.ptrace_scope = 1 the result will be like:
> > localhost /usr/local/bin # ./ptrace_test
> > TAP version 13
> > 1..8
> > # Starting 8 tests from 9 test cases.
> > #  RUN           hierarchy.allow_without_domain.trace ...
> > #      SKIP      unsupported yama value 1
> > #            OK  hierarchy.allow_without_domain.trace
> > ok 1 # SKIP unsupported yama value 1
> > #  RUN           hierarchy.allow_with_one_domain.trace ...
> > #            OK  hierarchy.allow_with_one_domain.trace
> > ok 2 hierarchy.allow_with_one_domain.trace
> > #  RUN           hierarchy.deny_with_parent_domain.trace ...
> > #      SKIP      unsupported yama value 1
> > #            OK  hierarchy.deny_with_parent_domain.trace
> > ok 3 # SKIP unsupported yama value 1
> > #  RUN           hierarchy.deny_with_sibling_domain.trace ...
> > #            OK  hierarchy.deny_with_sibling_domain.trace
> > ok 4 hierarchy.deny_with_sibling_domain.trace
> > #  RUN           hierarchy.allow_sibling_domain.trace ...
> > #      SKIP      unsupported yama value 1
> > #            OK  hierarchy.allow_sibling_domain.trace
> > ok 5 # SKIP unsupported yama value 1
> > #  RUN           hierarchy.allow_with_nested_domain.trace ...
> > #            OK  hierarchy.allow_with_nested_domain.trace
> > ok 6 hierarchy.allow_with_nested_domain.trace
> > #  RUN           hierarchy.deny_with_nested_and_parent_domain.trace ...
> > #      SKIP      unsupported yama value 1
> > #            OK  hierarchy.deny_with_nested_and_parent_domain.trace
> > ok 7 # SKIP unsupported yama value 1
> > #  RUN           hierarchy.deny_with_forked_domain.trace ...
> > #            OK  hierarchy.deny_with_forked_domain.trace
> > ok 8 hierarchy.deny_with_forked_domain.trace
> > # PASSED: 8 / 8 tests passed.
> > # Totals: pass:4 fail:0 xfail:0 xpass:0 skip:4 error:0
> >
> > when yama.ptrace_scope is 2:
> > localhost /usr/local/bin # sysctl kernel.yama.ptrace_scope=2
> > kernel.yama.ptrace_scope = 2
> > localhost /usr/local/bin # ./ptrace_test
> > TAP version 13
> > 1..8
> > # Starting 8 tests from 9 test cases.
> > #  RUN           hierarchy.allow_without_domain.trace ...
> > #      SKIP      unsupported yama value 2
> > #            OK  hierarchy.allow_without_domain.trace
> > ok 1 # SKIP unsupported yama value 2
> > #  RUN           hierarchy.allow_with_one_domain.trace ...
> > #      SKIP      unsupported yama value 2
> > #            OK  hierarchy.allow_with_one_domain.trace
> > ok 2 # SKIP unsupported yama value 2
> > #  RUN           hierarchy.deny_with_parent_domain.trace ...
> > #      SKIP      unsupported yama value 2
> > #            OK  hierarchy.deny_with_parent_domain.trace
> > ok 3 # SKIP unsupported yama value 2
> > #  RUN           hierarchy.deny_with_sibling_domain.trace ...
> > #            OK  hierarchy.deny_with_sibling_domain.trace
> > ok 4 hierarchy.deny_with_sibling_domain.trace
> > #  RUN           hierarchy.allow_sibling_domain.trace ...
> > #      SKIP      unsupported yama value 2
> > #            OK  hierarchy.allow_sibling_domain.trace
> > ok 5 # SKIP unsupported yama value 2
> > #  RUN           hierarchy.allow_with_nested_domain.trace ...
> > #      SKIP      unsupported yama value 2
> > #            OK  hierarchy.allow_with_nested_domain.trace
> > ok 6 # SKIP unsupported yama value 2
> > #  RUN           hierarchy.deny_with_nested_and_parent_domain.trace ...
> > #      SKIP      unsupported yama value 2
> > #            OK  hierarchy.deny_with_nested_and_parent_domain.trace
> > ok 7 # SKIP unsupported yama value 2
> > #  RUN           hierarchy.deny_with_forked_domain.trace ...
> > #            OK  hierarchy.deny_with_forked_domain.trace
> > ok 8 hierarchy.deny_with_forked_domain.trace
> > # PASSED: 8 / 8 tests passed.
> > # Totals: pass:2 fail:0 xfail:0 xpass:0 skip:6 error:0
> >
> >> This check skips the whole test, whereas the issues with Yama are about:
> >> - a child process tracing its parent;
> >> - the PTRACE_TRACEME case.
> >>
> >> I think the main remaining parts to change is the `if
> >> (variant->domain_*` checks to extend with the yama_ptrace_scope_max check.
> >>
> >> However, it is useful to highlight that a test didn't fully cover
> >> Landlock checks. I think the best approach is to call SKIP() at the end
> >> of TEST_F(hierarchy, trace) if yama_ptrace_scope >= 1 . This way, we
> >> test as much as possible (Landlock and Yama) and we mark the "tampered"
> >> tests as skipped.
> >>
> > I believe the test case should not have a lot of branches and logic
> > (if/else), which makes
> > the test case more complex and harder to read.  By that reason, SKIP()
> > is better at beginning
> > of the testcase.
>
> I agree in a general case, but here all the branches already exist to
> test all possible Landlock combinations. Adding Yama's ptrace scope will
> only update the existing branch conditions.
>
>
> >
> > Another reason is resource cleanup.  When SKIP() is not at the
> > beginning of tests,
> > the cleanup logic can get much more complicated because there are more
> > combinations of resource cleanup to
> > to be dealt with, after SKIP().
>
> All the logic for resource cleanup is already in place.
>
> >
> > Therefore I do not believe in "tests as much as possible" in a single
> > test, I would rather have a
> > dedicated test for the situation.
>
> The current test code already covers all possible combinations, so it is
> just a matter of extending the branch conditions. You can update these
> checks using dedicated booleans:
> - can_trace_child = !variant->domain_parent && (yama_ptrace_scope < 2);
> - can_trace_parent = !variant->domain_child && (yama_ptrace_scope < 1);
>
> …and at the end of all the hierarchy.trace tests add:
> if (yama_ptrace_scope > 0)
>         SKIP(return, "Incomplete tests due to Yama restrictions (ptrace_scope:
> %d)", yama_ptrace_scope);

OKey, I will update and send a new one.

Thanks
Jeff
diff mbox series

Patch

diff --git a/tools/testing/selftests/landlock/ptrace_test.c b/tools/testing/selftests/landlock/ptrace_test.c
index c28ef98ff3ac..8565a25a9587 100644
--- a/tools/testing/selftests/landlock/ptrace_test.c
+++ b/tools/testing/selftests/landlock/ptrace_test.c
@@ -60,6 +60,24 @@  static int test_ptrace_read(const pid_t pid)
 	return 0;
 }
 
+static int get_ptrace_scope(void)
+{
+	int ret = -1;
+	char buf[2];
+	int fd = open("/proc/sys/kernel/yama/ptrace_scope", O_RDONLY);
+
+	if (fd < 0)
+		return 0;
+
+	if (read(fd, &buf, 1) < 0)
+		return -1;
+
+	buf[1] = '\0';
+	ret = atoi(buf);
+	close(fd);
+	return ret;
+}
+
 /* clang-format off */
 FIXTURE(hierarchy) {};
 /* clang-format on */
@@ -69,6 +87,7 @@  FIXTURE_VARIANT(hierarchy)
 	const bool domain_both;
 	const bool domain_parent;
 	const bool domain_child;
+	const int  yama_value;
 };
 
 /*
@@ -93,6 +112,7 @@  FIXTURE_VARIANT_ADD(hierarchy, allow_without_domain) {
 	.domain_both = false,
 	.domain_parent = false,
 	.domain_child = false,
+	.yama_value = 0,
 };
 
 /*
@@ -110,6 +130,7 @@  FIXTURE_VARIANT_ADD(hierarchy, allow_with_one_domain) {
 	.domain_both = false,
 	.domain_parent = false,
 	.domain_child = true,
+	.yama_value = 1,
 };
 
 /*
@@ -126,6 +147,7 @@  FIXTURE_VARIANT_ADD(hierarchy, deny_with_parent_domain) {
 	.domain_both = false,
 	.domain_parent = true,
 	.domain_child = false,
+	.yama_value = 0,
 };
 
 /*
@@ -143,6 +165,7 @@  FIXTURE_VARIANT_ADD(hierarchy, deny_with_sibling_domain) {
 	.domain_both = false,
 	.domain_parent = true,
 	.domain_child = true,
+	.yama_value = 2,
 };
 
 /*
@@ -160,6 +183,7 @@  FIXTURE_VARIANT_ADD(hierarchy, allow_sibling_domain) {
 	.domain_both = true,
 	.domain_parent = false,
 	.domain_child = false,
+	.yama_value = 0,
 };
 
 /*
@@ -178,6 +202,7 @@  FIXTURE_VARIANT_ADD(hierarchy, allow_with_nested_domain) {
 	.domain_both = true,
 	.domain_parent = false,
 	.domain_child = true,
+	.yama_value = 1,
 };
 
 /*
@@ -196,6 +221,7 @@  FIXTURE_VARIANT_ADD(hierarchy, deny_with_nested_and_parent_domain) {
 	.domain_both = true,
 	.domain_parent = true,
 	.domain_child = false,
+	.yama_value = 0,
 };
 
 /*
@@ -216,6 +242,7 @@  FIXTURE_VARIANT_ADD(hierarchy, deny_with_forked_domain) {
 	.domain_both = true,
 	.domain_parent = true,
 	.domain_child = true,
+	.yama_value = 2,
 };
 
 FIXTURE_SETUP(hierarchy)
@@ -232,9 +259,16 @@  TEST_F(hierarchy, trace)
 	pid_t child, parent;
 	int status, err_proc_read;
 	int pipe_child[2], pipe_parent[2];
+	int yama;
 	char buf_parent;
 	long ret;
 
+	yama = get_ptrace_scope();
+	ASSERT_LE(0, yama);
+
+	if (variant->yama_value < yama)
+		SKIP(return, "unsupported yama value %d", yama);
+
 	/*
 	 * Removes all effective and permitted capabilities to not interfere
 	 * with cap_ptrace_access_check() in case of PTRACE_MODE_FSCREDS.