Patchwork [v2] LSM: Enable multiple calls to security_add_hooks() for the same LSM

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Submitter Mickaël Salaün
Date May 9, 2017, 11:08 p.m.
Message ID <20170509230853.8017-1-mic@digikod.net>
Download mbox | patch
Permalink /patch/9719003/
State New
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Comments

Mickaël Salaün - May 9, 2017, 11:08 p.m.
The commit d69dece5f5b6 ("LSM: Add /sys/kernel/security/lsm") extend
security_add_hooks() with a new parameter to register the LSM name,
which may be useful to make the list of currently loaded LSM available
to userspace. However, there is no clean way for an LSM to split its
hook declarations into multiple files, which may reduce the mess with
all the included files (needed for LSM hook argument types) and make the
source code easier to review and maintain.

This change allows an LSM to register multiple times its hook while
keeping a consistent list of LSM names as described in
Documentation/security/LSM.txt . The list reflects the order in which
checks are made. This patch only check for the last registered LSM. If
an LSM register multiple times its hooks, interleaved with other LSM
registrations (which should not happen), its name will still appear in
the same order that the hooks are called, hence multiple times.

To sum up, "capability,selinux,foo,foo" will be replaced with
"capability,selinux,foo", however "capability,foo,selinux,foo" will
remain as is.

Signed-off-by: Mickaël Salaün <mic@digikod.net>
Cc: Casey Schaufler <casey@schaufler-ca.com>
Cc: James Morris <james.l.morris@oracle.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Serge E. Hallyn <serge@hallyn.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Link: https://lkml.kernel.org/r/ccad825b-7a58-e499-e51b-bd7c98581afe@schaufler-ca.com
---
 security/security.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)
Kees Cook - May 9, 2017, 11:35 p.m.
On Tue, May 9, 2017 at 4:08 PM, Mickaël Salaün <mic@digikod.net> wrote:
> The commit d69dece5f5b6 ("LSM: Add /sys/kernel/security/lsm") extend
> security_add_hooks() with a new parameter to register the LSM name,
> which may be useful to make the list of currently loaded LSM available
> to userspace. However, there is no clean way for an LSM to split its
> hook declarations into multiple files, which may reduce the mess with
> all the included files (needed for LSM hook argument types) and make the
> source code easier to review and maintain.
>
> This change allows an LSM to register multiple times its hook while
> keeping a consistent list of LSM names as described in
> Documentation/security/LSM.txt . The list reflects the order in which
> checks are made. This patch only check for the last registered LSM. If
> an LSM register multiple times its hooks, interleaved with other LSM
> registrations (which should not happen), its name will still appear in
> the same order that the hooks are called, hence multiple times.
>
> To sum up, "capability,selinux,foo,foo" will be replaced with
> "capability,selinux,foo", however "capability,foo,selinux,foo" will
> remain as is.
>
> Signed-off-by: Mickaël Salaün <mic@digikod.net>
> Cc: Casey Schaufler <casey@schaufler-ca.com>
> Cc: James Morris <james.l.morris@oracle.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Serge E. Hallyn <serge@hallyn.com>
> Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
> Link: https://lkml.kernel.org/r/ccad825b-7a58-e499-e51b-bd7c98581afe@schaufler-ca.com
> ---
>  security/security.c | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
>
> diff --git a/security/security.c b/security/security.c
> index 549bddcc2116..6be65050b268 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -25,6 +25,7 @@
>  #include <linux/mount.h>
>  #include <linux/personality.h>
>  #include <linux/backing-dev.h>
> +#include <linux/string.h>
>  #include <net/flow.h>
>
>  #define MAX_LSM_EVM_XATTR      2
> @@ -86,6 +87,32 @@ static int __init choose_lsm(char *str)
>  }
>  __setup("security=", choose_lsm);
>
> +static bool match_last_lsm(const char *list, const char *last)
> +{
> +       size_t list_len, last_len, i;
> +
> +       if (!list || !last)
> +               return false;
> +       list_len = strlen(list);
> +       last_len = strlen(last);
> +       if (!last_len || !list_len)
> +               return false;
> +       if (last_len > list_len)
> +               return false;
> +
> +       for (i = 0; i < last_len; i++) {
> +               if (list[list_len - 1 - i] != last[last_len - 1 - i])
> +                       return false;
> +       }
> +       /* Check if last_len == list_len */
> +       if (i == list_len)
> +               return true;
> +       /* Check if it is a full name */
> +       if (list[list_len - 1 - i] == ',')
> +               return true;
> +       return false;
> +}

This could be reduced to just:

static bool match_last_lsm(const char *list, const char *lsm)
{
    char *last;

    last = strrchr(list, ',') ?: list;

    return (strcmp(last, lsm) == 0);
}

> +
>  static int lsm_append(char *new, char **result)
>  {
>         char *cp;
> @@ -93,6 +120,9 @@ static int lsm_append(char *new, char **result)
>         if (*result == NULL) {
>                 *result = kstrdup(new, GFP_KERNEL);
>         } else {
> +               /* Check if it is the last registered name */
> +               if (match_last_lsm(*result, new))
> +                       return 0;
>                 cp = kasprintf(GFP_KERNEL, "%s,%s", *result, new);
>                 if (cp == NULL)
>                         return -ENOMEM;
> --
> 2.11.0
>
Mickaël Salaün - May 10, 2017, 6:33 a.m.
On 10/05/2017 01:35, Kees Cook wrote:
> On Tue, May 9, 2017 at 4:08 PM, Mickaël Salaün <mic@digikod.net> wrote:
>> The commit d69dece5f5b6 ("LSM: Add /sys/kernel/security/lsm") extend
>> security_add_hooks() with a new parameter to register the LSM name,
>> which may be useful to make the list of currently loaded LSM available
>> to userspace. However, there is no clean way for an LSM to split its
>> hook declarations into multiple files, which may reduce the mess with
>> all the included files (needed for LSM hook argument types) and make the
>> source code easier to review and maintain.
>>
>> This change allows an LSM to register multiple times its hook while
>> keeping a consistent list of LSM names as described in
>> Documentation/security/LSM.txt . The list reflects the order in which
>> checks are made. This patch only check for the last registered LSM. If
>> an LSM register multiple times its hooks, interleaved with other LSM
>> registrations (which should not happen), its name will still appear in
>> the same order that the hooks are called, hence multiple times.
>>
>> To sum up, "capability,selinux,foo,foo" will be replaced with
>> "capability,selinux,foo", however "capability,foo,selinux,foo" will
>> remain as is.
>>
>> Signed-off-by: Mickaël Salaün <mic@digikod.net>
>> Cc: Casey Schaufler <casey@schaufler-ca.com>
>> Cc: James Morris <james.l.morris@oracle.com>
>> Cc: Kees Cook <keescook@chromium.org>
>> Cc: Serge E. Hallyn <serge@hallyn.com>
>> Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
>> Link: https://lkml.kernel.org/r/ccad825b-7a58-e499-e51b-bd7c98581afe@schaufler-ca.com
>> ---
>>  security/security.c | 30 ++++++++++++++++++++++++++++++
>>  1 file changed, 30 insertions(+)
>>
>> diff --git a/security/security.c b/security/security.c
>> index 549bddcc2116..6be65050b268 100644
>> --- a/security/security.c
>> +++ b/security/security.c
>> @@ -25,6 +25,7 @@
>>  #include <linux/mount.h>
>>  #include <linux/personality.h>
>>  #include <linux/backing-dev.h>
>> +#include <linux/string.h>
>>  #include <net/flow.h>
>>
>>  #define MAX_LSM_EVM_XATTR      2
>> @@ -86,6 +87,32 @@ static int __init choose_lsm(char *str)
>>  }
>>  __setup("security=", choose_lsm);
>>
>> +static bool match_last_lsm(const char *list, const char *last)
>> +{
>> +       size_t list_len, last_len, i;
>> +
>> +       if (!list || !last)
>> +               return false;
>> +       list_len = strlen(list);
>> +       last_len = strlen(last);
>> +       if (!last_len || !list_len)
>> +               return false;
>> +       if (last_len > list_len)
>> +               return false;
>> +
>> +       for (i = 0; i < last_len; i++) {
>> +               if (list[list_len - 1 - i] != last[last_len - 1 - i])
>> +                       return false;
>> +       }
>> +       /* Check if last_len == list_len */
>> +       if (i == list_len)
>> +               return true;
>> +       /* Check if it is a full name */
>> +       if (list[list_len - 1 - i] == ',')
>> +               return true;
>> +       return false;
>> +}
> 
> This could be reduced to just:
> 
> static bool match_last_lsm(const char *list, const char *lsm)
> {
>     char *last;
> 
>     last = strrchr(list, ',') ?: list;
> 
>     return (strcmp(last, lsm) == 0);
> }

Indeed, almost the same, I just need to increment and check "last" to
make it work. :)
I'll keep the initial NULL checks, wrap them with a WARN_ON() and use a
const "last", though. It will be much more readable, thanks!

> 
>> +
>>  static int lsm_append(char *new, char **result)
>>  {
>>         char *cp;
>> @@ -93,6 +120,9 @@ static int lsm_append(char *new, char **result)
>>         if (*result == NULL) {
>>                 *result = kstrdup(new, GFP_KERNEL);
>>         } else {
>> +               /* Check if it is the last registered name */
>> +               if (match_last_lsm(*result, new))
>> +                       return 0;
>>                 cp = kasprintf(GFP_KERNEL, "%s,%s", *result, new);
>>                 if (cp == NULL)
>>                         return -ENOMEM;
>> --
>> 2.11.0
>>
> 
> 
>

Patch

diff --git a/security/security.c b/security/security.c
index 549bddcc2116..6be65050b268 100644
--- a/security/security.c
+++ b/security/security.c
@@ -25,6 +25,7 @@ 
 #include <linux/mount.h>
 #include <linux/personality.h>
 #include <linux/backing-dev.h>
+#include <linux/string.h>
 #include <net/flow.h>
 
 #define MAX_LSM_EVM_XATTR	2
@@ -86,6 +87,32 @@  static int __init choose_lsm(char *str)
 }
 __setup("security=", choose_lsm);
 
+static bool match_last_lsm(const char *list, const char *last)
+{
+	size_t list_len, last_len, i;
+
+	if (!list || !last)
+		return false;
+	list_len = strlen(list);
+	last_len = strlen(last);
+	if (!last_len || !list_len)
+		return false;
+	if (last_len > list_len)
+		return false;
+
+	for (i = 0; i < last_len; i++) {
+		if (list[list_len - 1 - i] != last[last_len - 1 - i])
+			return false;
+	}
+	/* Check if last_len == list_len */
+	if (i == list_len)
+		return true;
+	/* Check if it is a full name */
+	if (list[list_len - 1 - i] == ',')
+		return true;
+	return false;
+}
+
 static int lsm_append(char *new, char **result)
 {
 	char *cp;
@@ -93,6 +120,9 @@  static int lsm_append(char *new, char **result)
 	if (*result == NULL) {
 		*result = kstrdup(new, GFP_KERNEL);
 	} else {
+		/* Check if it is the last registered name */
+		if (match_last_lsm(*result, new))
+			return 0;
 		cp = kasprintf(GFP_KERNEL, "%s,%s", *result, new);
 		if (cp == NULL)
 			return -ENOMEM;