| Message ID | 20200327172331.418878-9-gladkov.alexey@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | proc: modernize proc to support multiple private instances | expand |
On Fri, Mar 27, 2020 at 06:23:30PM +0100, Alexey Gladkov wrote: > The hidepid parameter values are becoming more and more and it becomes > difficult to remember what each new magic number means. > > Suggested-by: Andy Lutomirski <luto@kernel.org> > Reviewed-by: Alexey Dobriyan <adobriyan@gmail.com> > Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com> > --- > Documentation/filesystems/proc.txt | 52 +++++++++++++++--------------- > fs/proc/inode.c | 13 +++++++- > fs/proc/root.c | 36 +++++++++++++++++++-- > 3 files changed, 71 insertions(+), 30 deletions(-) > > diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt > index bd0e0ab85048..af47672cb2cb 100644 > --- a/Documentation/filesystems/proc.txt > +++ b/Documentation/filesystems/proc.txt > @@ -2025,28 +2025,28 @@ The following mount options are supported: > gid= Set the group authorized to learn processes information. > subset= Show only the specified subset of procfs. > > -hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories > -(default). > - > -hidepid=1 means users may not access any /proc/<pid>/ directories but their > -own. Sensitive files like cmdline, sched*, status are now protected against > -other users. This makes it impossible to learn whether any user runs > -specific program (given the program doesn't reveal itself by its behaviour). > -As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users, > -poorly written programs passing sensitive information via program arguments are > -now protected against local eavesdroppers. > - > -hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other > -users. It doesn't mean that it hides a fact whether a process with a specific > -pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"), > -but it hides process' uid and gid, which may be learned by stat()'ing > -/proc/<pid>/ otherwise. It greatly complicates an intruder's task of gathering > -information about running processes, whether some daemon runs with elevated > -privileges, whether other user runs some sensitive program, whether other users > -run any program at all, etc. > - > -hidepid=4 means that procfs should only contain /proc/<pid>/ directories > -that the caller can ptrace. > +hidepid=off or hidepid=0 means classic mode - everybody may access all > +/proc/<pid>/ directories (default). > + > +hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/ > +directories but their own. Sensitive files like cmdline, sched*, status are now > +protected against other users. This makes it impossible to learn whether any > +user runs specific program (given the program doesn't reveal itself by its > +behaviour). As an additional bonus, as /proc/<pid>/cmdline is unaccessible for > +other users, poorly written programs passing sensitive information via program > +arguments are now protected against local eavesdroppers. > + > +hidepid=invisible or hidepid=2 means hidepid=noaccess plus all /proc/<pid>/ will > +be fully invisible to other users. It doesn't mean that it hides a fact whether > +a process with a specific pid value exists (it can be learned by other means, > +e.g. by "kill -0 $PID"), but it hides process' uid and gid, which may be learned > +by stat()'ing /proc/<pid>/ otherwise. It greatly complicates an intruder's task > +of gathering information about running processes, whether some daemon runs with > +elevated privileges, whether other user runs some sensitive program, whether > +other users run any program at all, etc. > + > +hidepid=ptraceable or hidepid=4 means that procfs should only contain > +/proc/<pid>/ directories that the caller can ptrace. > > gid= defines a group authorized to learn processes information otherwise > prohibited by hidepid=. If you use some daemon like identd which needs to learn > @@ -2093,8 +2093,8 @@ creates a new procfs instance. Mount options affect own procfs instance. > It means that it became possible to have several procfs instances > displaying tasks with different filtering options in one pid namespace. > > -# mount -o hidepid=2 -t proc proc /proc > -# mount -o hidepid=1 -t proc proc /tmp/proc > +# mount -o hidepid=invisible -t proc proc /proc > +# mount -o hidepid=noaccess -t proc proc /tmp/proc > # grep ^proc /proc/mounts > -proc /proc proc rw,relatime,hidepid=2 0 0 > -proc /tmp/proc proc rw,relatime,hidepid=1 0 0 > +proc /proc proc rw,relatime,hidepid=invisible 0 0 > +proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0 > diff --git a/fs/proc/inode.c b/fs/proc/inode.c > index e6577ce6027b..f01fb4bed75c 100644 > --- a/fs/proc/inode.c > +++ b/fs/proc/inode.c > @@ -165,6 +165,17 @@ void proc_invalidate_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock > deactivate_super(old_sb); > } > > +static inline const char *hidepid2str(int v) > +{ > + switch (v) { > + case HIDEPID_OFF: return "off"; > + case HIDEPID_NO_ACCESS: return "noaccess"; > + case HIDEPID_INVISIBLE: return "invisible"; > + case HIDEPID_NOT_PTRACEABLE: return "ptraceable"; > + } > + BUG(); Please don't use BUG()[1]. Add a default case with a warn and return "unknown": switch (v) { case HIDEPID_OFF: return "off"; case HIDEPID_NO_ACCESS: return "noaccess"; case HIDEPID_INVISIBLE: return "invisible"; case HIDEPID_NOT_PTRACEABLE: return "ptraceable"; default: WARN_ON_ONCE("bad hide_pid value: %d\n", v); return "unknown"; } [1] https://lore.kernel.org/lkml/202003141524.59C619B51A@keescook/ > +} > + > static int proc_show_options(struct seq_file *seq, struct dentry *root) > { > struct proc_fs_info *fs_info = proc_sb_info(root->d_sb); > @@ -172,7 +183,7 @@ static int proc_show_options(struct seq_file *seq, struct dentry *root) > if (!gid_eq(fs_info->pid_gid, GLOBAL_ROOT_GID)) > seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, fs_info->pid_gid)); > if (fs_info->hide_pid != HIDEPID_OFF) > - seq_printf(seq, ",hidepid=%u", fs_info->hide_pid); > + seq_printf(seq, ",hidepid=%s", hidepid2str(fs_info->hide_pid)); > if (fs_info->pidonly != PROC_PIDONLY_OFF) > seq_printf(seq, ",subset=pid"); > > diff --git a/fs/proc/root.c b/fs/proc/root.c > index dbcd96f07c7a..ba782d6e6197 100644 > --- a/fs/proc/root.c > +++ b/fs/proc/root.c > @@ -45,7 +45,7 @@ enum proc_param { > > static const struct fs_parameter_spec proc_fs_parameters[] = { > fsparam_u32("gid", Opt_gid), > - fsparam_u32("hidepid", Opt_hidepid), > + fsparam_string("hidepid", Opt_hidepid), > fsparam_string("subset", Opt_subset), > {} > }; > @@ -58,6 +58,35 @@ static inline int valid_hidepid(unsigned int value) > value == HIDEPID_NOT_PTRACEABLE); > } > > +static int proc_parse_hidepid_param(struct fs_context *fc, struct fs_parameter *param) > +{ > + struct proc_fs_context *ctx = fc->fs_private; > + struct fs_parameter_spec hidepid_u32_spec = fsparam_u32("hidepid", Opt_hidepid); > + struct fs_parse_result result; > + int base = (unsigned long)hidepid_u32_spec.data; > + > + if (param->type != fs_value_is_string) > + return invalf(fc, "proc: unexpected type of hidepid value\n"); > + > + if (!kstrtouint(param->string, base, &result.uint_32)) { > + ctx->hidepid = result.uint_32; This need to bounds-check the value with a call to valid_hidepid(), yes? > + return 0; > + } > + > + if (!strcmp(param->string, "off")) > + ctx->hidepid = HIDEPID_OFF; > + else if (!strcmp(param->string, "noaccess")) > + ctx->hidepid = HIDEPID_NO_ACCESS; > + else if (!strcmp(param->string, "invisible")) > + ctx->hidepid = HIDEPID_INVISIBLE; > + else if (!strcmp(param->string, "ptraceable")) > + ctx->hidepid = HIDEPID_NOT_PTRACEABLE; > + else > + return invalf(fc, "proc: unknown value of hidepid - %s\n", param->string); > + > + return 0; > +} > + > static int proc_parse_subset_param(struct fs_context *fc, char *value) > { > struct proc_fs_context *ctx = fc->fs_private; > @@ -97,9 +126,10 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param) > break; > > case Opt_hidepid: > - if (!valid_hidepid(result.uint_32)) > + if (proc_parse_hidepid_param(fc, param)) > + return -EINVAL; > + if (!valid_hidepid(ctx->hidepid)) > return invalf(fc, "proc: unknown value of hidepid.\n"); > - ctx->hidepid = result.uint_32; > break; > > case Opt_subset: > -- > 2.25.2 >
On Sat, Mar 28, 2020 at 01:28:28PM -0700, Kees Cook wrote: > On Fri, Mar 27, 2020 at 06:23:30PM +0100, Alexey Gladkov wrote: > > The hidepid parameter values are becoming more and more and it becomes > > difficult to remember what each new magic number means. > > > > Suggested-by: Andy Lutomirski <luto@kernel.org> > > Reviewed-by: Alexey Dobriyan <adobriyan@gmail.com> > > Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com> > > --- > > Documentation/filesystems/proc.txt | 52 +++++++++++++++--------------- > > fs/proc/inode.c | 13 +++++++- > > fs/proc/root.c | 36 +++++++++++++++++++-- > > 3 files changed, 71 insertions(+), 30 deletions(-) > > > > diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt > > index bd0e0ab85048..af47672cb2cb 100644 > > --- a/Documentation/filesystems/proc.txt > > +++ b/Documentation/filesystems/proc.txt > > @@ -2025,28 +2025,28 @@ The following mount options are supported: > > gid= Set the group authorized to learn processes information. > > subset= Show only the specified subset of procfs. > > > > -hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories > > -(default). > > - > > -hidepid=1 means users may not access any /proc/<pid>/ directories but their > > -own. Sensitive files like cmdline, sched*, status are now protected against > > -other users. This makes it impossible to learn whether any user runs > > -specific program (given the program doesn't reveal itself by its behaviour). > > -As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users, > > -poorly written programs passing sensitive information via program arguments are > > -now protected against local eavesdroppers. > > - > > -hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other > > -users. It doesn't mean that it hides a fact whether a process with a specific > > -pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"), > > -but it hides process' uid and gid, which may be learned by stat()'ing > > -/proc/<pid>/ otherwise. It greatly complicates an intruder's task of gathering > > -information about running processes, whether some daemon runs with elevated > > -privileges, whether other user runs some sensitive program, whether other users > > -run any program at all, etc. > > - > > -hidepid=4 means that procfs should only contain /proc/<pid>/ directories > > -that the caller can ptrace. > > +hidepid=off or hidepid=0 means classic mode - everybody may access all > > +/proc/<pid>/ directories (default). > > + > > +hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/ > > +directories but their own. Sensitive files like cmdline, sched*, status are now > > +protected against other users. This makes it impossible to learn whether any > > +user runs specific program (given the program doesn't reveal itself by its > > +behaviour). As an additional bonus, as /proc/<pid>/cmdline is unaccessible for > > +other users, poorly written programs passing sensitive information via program > > +arguments are now protected against local eavesdroppers. > > + > > +hidepid=invisible or hidepid=2 means hidepid=noaccess plus all /proc/<pid>/ will > > +be fully invisible to other users. It doesn't mean that it hides a fact whether > > +a process with a specific pid value exists (it can be learned by other means, > > +e.g. by "kill -0 $PID"), but it hides process' uid and gid, which may be learned > > +by stat()'ing /proc/<pid>/ otherwise. It greatly complicates an intruder's task > > +of gathering information about running processes, whether some daemon runs with > > +elevated privileges, whether other user runs some sensitive program, whether > > +other users run any program at all, etc. > > + > > +hidepid=ptraceable or hidepid=4 means that procfs should only contain > > +/proc/<pid>/ directories that the caller can ptrace. > > > > gid= defines a group authorized to learn processes information otherwise > > prohibited by hidepid=. If you use some daemon like identd which needs to learn > > @@ -2093,8 +2093,8 @@ creates a new procfs instance. Mount options affect own procfs instance. > > It means that it became possible to have several procfs instances > > displaying tasks with different filtering options in one pid namespace. > > > > -# mount -o hidepid=2 -t proc proc /proc > > -# mount -o hidepid=1 -t proc proc /tmp/proc > > +# mount -o hidepid=invisible -t proc proc /proc > > +# mount -o hidepid=noaccess -t proc proc /tmp/proc > > # grep ^proc /proc/mounts > > -proc /proc proc rw,relatime,hidepid=2 0 0 > > -proc /tmp/proc proc rw,relatime,hidepid=1 0 0 > > +proc /proc proc rw,relatime,hidepid=invisible 0 0 > > +proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0 > > diff --git a/fs/proc/inode.c b/fs/proc/inode.c > > index e6577ce6027b..f01fb4bed75c 100644 > > --- a/fs/proc/inode.c > > +++ b/fs/proc/inode.c > > @@ -165,6 +165,17 @@ void proc_invalidate_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock > > deactivate_super(old_sb); > > } > > > > +static inline const char *hidepid2str(int v) > > +{ > > + switch (v) { > > + case HIDEPID_OFF: return "off"; > > + case HIDEPID_NO_ACCESS: return "noaccess"; > > + case HIDEPID_INVISIBLE: return "invisible"; > > + case HIDEPID_NOT_PTRACEABLE: return "ptraceable"; > > + } > > + BUG(); > > Please don't use BUG()[1]. Add a default case with a warn and return > "unknown": > > switch (v) { > case HIDEPID_OFF: return "off"; > case HIDEPID_NO_ACCESS: return "noaccess"; > case HIDEPID_INVISIBLE: return "invisible"; > case HIDEPID_NOT_PTRACEABLE: return "ptraceable"; > default: > WARN_ON_ONCE("bad hide_pid value: %d\n", v); > return "unknown"; > } > > [1] https://lore.kernel.org/lkml/202003141524.59C619B51A@keescook/ Make sense. I will change it. > > +} > > + > > static int proc_show_options(struct seq_file *seq, struct dentry *root) > > { > > struct proc_fs_info *fs_info = proc_sb_info(root->d_sb); > > @@ -172,7 +183,7 @@ static int proc_show_options(struct seq_file *seq, struct dentry *root) > > if (!gid_eq(fs_info->pid_gid, GLOBAL_ROOT_GID)) > > seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, fs_info->pid_gid)); > > if (fs_info->hide_pid != HIDEPID_OFF) > > - seq_printf(seq, ",hidepid=%u", fs_info->hide_pid); > > + seq_printf(seq, ",hidepid=%s", hidepid2str(fs_info->hide_pid)); > > if (fs_info->pidonly != PROC_PIDONLY_OFF) > > seq_printf(seq, ",subset=pid"); > > > > diff --git a/fs/proc/root.c b/fs/proc/root.c > > index dbcd96f07c7a..ba782d6e6197 100644 > > --- a/fs/proc/root.c > > +++ b/fs/proc/root.c > > @@ -45,7 +45,7 @@ enum proc_param { > > > > static const struct fs_parameter_spec proc_fs_parameters[] = { > > fsparam_u32("gid", Opt_gid), > > - fsparam_u32("hidepid", Opt_hidepid), > > + fsparam_string("hidepid", Opt_hidepid), > > fsparam_string("subset", Opt_subset), > > {} > > }; > > @@ -58,6 +58,35 @@ static inline int valid_hidepid(unsigned int value) > > value == HIDEPID_NOT_PTRACEABLE); > > } > > > > +static int proc_parse_hidepid_param(struct fs_context *fc, struct fs_parameter *param) > > +{ > > + struct proc_fs_context *ctx = fc->fs_private; > > + struct fs_parameter_spec hidepid_u32_spec = fsparam_u32("hidepid", Opt_hidepid); > > + struct fs_parse_result result; > > + int base = (unsigned long)hidepid_u32_spec.data; > > + > > + if (param->type != fs_value_is_string) > > + return invalf(fc, "proc: unexpected type of hidepid value\n"); > > + > > + if (!kstrtouint(param->string, base, &result.uint_32)) { > > + ctx->hidepid = result.uint_32; > > This need to bounds-check the value with a call to valid_hidepid(), yes? The kstrtouint returns 0 on success and -ERANGE on overflow [1]. [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/kstrtox.c#n217 > > + return 0; > > + } > > + > > + if (!strcmp(param->string, "off")) > > + ctx->hidepid = HIDEPID_OFF; > > + else if (!strcmp(param->string, "noaccess")) > > + ctx->hidepid = HIDEPID_NO_ACCESS; > > + else if (!strcmp(param->string, "invisible")) > > + ctx->hidepid = HIDEPID_INVISIBLE; > > + else if (!strcmp(param->string, "ptraceable")) > > + ctx->hidepid = HIDEPID_NOT_PTRACEABLE; > > + else > > + return invalf(fc, "proc: unknown value of hidepid - %s\n", param->string); > > + > > + return 0; > > +} > > + > > static int proc_parse_subset_param(struct fs_context *fc, char *value) > > { > > struct proc_fs_context *ctx = fc->fs_private; > > @@ -97,9 +126,10 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param) > > break; > > > > case Opt_hidepid: > > - if (!valid_hidepid(result.uint_32)) > > + if (proc_parse_hidepid_param(fc, param)) > > + return -EINVAL; > > + if (!valid_hidepid(ctx->hidepid)) > > return invalf(fc, "proc: unknown value of hidepid.\n"); > > - ctx->hidepid = result.uint_32; > > break; > > > > case Opt_subset: > > -- > > 2.25.2 > > > > -- > Kees Cook >
On Sat, Mar 28, 2020 at 10:14:53PM +0100, Alexey Gladkov wrote: > On Sat, Mar 28, 2020 at 01:28:28PM -0700, Kees Cook wrote: > > On Fri, Mar 27, 2020 at 06:23:30PM +0100, Alexey Gladkov wrote: > > > [...] > > > + if (!kstrtouint(param->string, base, &result.uint_32)) { > > > + ctx->hidepid = result.uint_32; > > > > This need to bounds-check the value with a call to valid_hidepid(), yes? > > The kstrtouint returns 0 on success and -ERANGE on overflow [1]. No, I mean, hidepid cannot be just any uint32 value. It must be in the enum. Is that checked somewhere else? It looked like the call to valid_hidepid() was removed.
On Sat, Mar 28, 2020 at 02:52:55PM -0700, Kees Cook wrote: > On Sat, Mar 28, 2020 at 10:14:53PM +0100, Alexey Gladkov wrote: > > On Sat, Mar 28, 2020 at 01:28:28PM -0700, Kees Cook wrote: > > > On Fri, Mar 27, 2020 at 06:23:30PM +0100, Alexey Gladkov wrote: > > > > [...] > > > > + if (!kstrtouint(param->string, base, &result.uint_32)) { > > > > + ctx->hidepid = result.uint_32; > > > > > > This need to bounds-check the value with a call to valid_hidepid(), yes? > > > > The kstrtouint returns 0 on success and -ERANGE on overflow [1]. > > No, I mean, hidepid cannot be just any uint32 value. It must be in the > enum. Is that checked somewhere else? It looked like the call to > valid_hidepid() was removed. The valid_hidepid() is called after parsing the hidepid parameter value. Yes, it can be called inside this condition.
Alexey Gladkov <gladkov.alexey@gmail.com> writes: > The hidepid parameter values are becoming more and more and it becomes > difficult to remember what each new magic number means. In principle I like this change. In practice I think you have just broken ABI compatiblity with the new mount ABI. In particular the following line seems broken. > diff --git a/fs/proc/root.c b/fs/proc/root.c > index dbcd96f07c7a..ba782d6e6197 100644 > --- a/fs/proc/root.c > +++ b/fs/proc/root.c > @@ -45,7 +45,7 @@ enum proc_param { > > static const struct fs_parameter_spec proc_fs_parameters[] = { > fsparam_u32("gid", Opt_gid), > - fsparam_u32("hidepid", Opt_hidepid), > + fsparam_string("hidepid", Opt_hidepid), > fsparam_string("subset", Opt_subset), > {} > }; As I read fs_parser.c fs_param_is_u32 handles string inputs and turns them into numbers, and it handles binary numbers. However fs_param_is_string appears to only handle strings. It appears to have not capacity to turn raw binary numbers into strings. So I think we probably need to fix fs_param_is_string to raw binary numbers before we can safely make this change to fs/proc/root.c David am I reading the fs_parser.c code correctly? If I am are you ok with a change like the above? Eric
On Thu, Apr 02, 2020 at 11:05:21AM -0500, Eric W. Biederman wrote: > Alexey Gladkov <gladkov.alexey@gmail.com> writes: > > > The hidepid parameter values are becoming more and more and it becomes > > difficult to remember what each new magic number means. > > In principle I like this change. In practice I think you have just > broken ABI compatiblity with the new mount ABI. > > In particular the following line seems broken. > > > diff --git a/fs/proc/root.c b/fs/proc/root.c > > index dbcd96f07c7a..ba782d6e6197 100644 > > --- a/fs/proc/root.c > > +++ b/fs/proc/root.c > > @@ -45,7 +45,7 @@ enum proc_param { > > > > static const struct fs_parameter_spec proc_fs_parameters[] = { > > fsparam_u32("gid", Opt_gid), > > - fsparam_u32("hidepid", Opt_hidepid), > > + fsparam_string("hidepid", Opt_hidepid), > > fsparam_string("subset", Opt_subset), > > {} > > }; > > As I read fs_parser.c fs_param_is_u32 handles string inputs and turns them > into numbers, and it handles binary numbers. However fs_param_is_string > appears to only handle strings. It appears to have not capacity to turn > raw binary numbers into strings. I use result only with hidepid_u32_spec and nobody modifies param->string. I do not use internal functions here. I don’t follow how a raw number can get here ? > So I think we probably need to fix fs_param_is_string to raw binary > numbers before we can safely make this change to fs/proc/root.c > > David am I reading the fs_parser.c code correctly? If I am are you ok > with a change like the above? > > Eric >
Alexey Gladkov <gladkov.alexey@gmail.com> writes: > On Thu, Apr 02, 2020 at 11:05:21AM -0500, Eric W. Biederman wrote: >> Alexey Gladkov <gladkov.alexey@gmail.com> writes: >> >> > The hidepid parameter values are becoming more and more and it becomes >> > difficult to remember what each new magic number means. >> >> In principle I like this change. In practice I think you have just >> broken ABI compatiblity with the new mount ABI. >> >> In particular the following line seems broken. >> >> > diff --git a/fs/proc/root.c b/fs/proc/root.c >> > index dbcd96f07c7a..ba782d6e6197 100644 >> > --- a/fs/proc/root.c >> > +++ b/fs/proc/root.c >> > @@ -45,7 +45,7 @@ enum proc_param { >> > >> > static const struct fs_parameter_spec proc_fs_parameters[] = { >> > fsparam_u32("gid", Opt_gid), >> > - fsparam_u32("hidepid", Opt_hidepid), >> > + fsparam_string("hidepid", Opt_hidepid), >> > fsparam_string("subset", Opt_subset), >> > {} >> > }; >> >> As I read fs_parser.c fs_param_is_u32 handles string inputs and turns them >> into numbers, and it handles binary numbers. However fs_param_is_string >> appears to only handle strings. It appears to have not capacity to turn >> raw binary numbers into strings. > > I use result only with hidepid_u32_spec and nobody modifies param->string. > I do not use internal functions here. > > I don’t follow how a raw number can get here ? I may be wrong but last I looked you can input raw numbers using the new mount api. I have most of the details paged out at the moment, but I believe that is why when you set a parameter in the new mount api it takes a type. >> So I think we probably need to fix fs_param_is_string to raw binary >> numbers before we can safely make this change to fs/proc/root.c >> >> David am I reading the fs_parser.c code correctly? If I am are you ok >> with a change like the above? Eric
On Thu, Apr 02, 2020 at 11:05:21AM -0500, Eric W. Biederman wrote: > Alexey Gladkov <gladkov.alexey@gmail.com> writes: > > > The hidepid parameter values are becoming more and more and it becomes > > difficult to remember what each new magic number means. > > In principle I like this change. In practice I think you have just > broken ABI compatiblity with the new mount ABI. > > In particular the following line seems broken. > > > diff --git a/fs/proc/root.c b/fs/proc/root.c > > index dbcd96f07c7a..ba782d6e6197 100644 > > --- a/fs/proc/root.c > > +++ b/fs/proc/root.c > > @@ -45,7 +45,7 @@ enum proc_param { > > > > static const struct fs_parameter_spec proc_fs_parameters[] = { > > fsparam_u32("gid", Opt_gid), > > - fsparam_u32("hidepid", Opt_hidepid), > > + fsparam_string("hidepid", Opt_hidepid), > > fsparam_string("subset", Opt_subset), > > {} > > }; > > As I read fs_parser.c fs_param_is_u32 handles string inputs and turns them > into numbers, and it handles binary numbers. Yes, you can use: fsconfig(fsfd, FSCONFIG_SET_BINARY, ...); but in this case the type of parameter will be fs_value_is_blob [1]. This kind of parameters is handled by fs_param_is_blob(). The fs_param_is_u32 can handle only parametes with fs_value_is_string type [2]. Am I missing something? [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/fsopen.c#n405 [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/fs_parser.c#n215 > However fs_param_is_string > appears to only handle strings. It appears to have not capacity to turn > raw binary numbers into strings. > > So I think we probably need to fix fs_param_is_string to raw binary > numbers before we can safely make this change to fs/proc/root.c > > David am I reading the fs_parser.c code correctly? If I am are you ok > with a change like the above? > > Eric >
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index bd0e0ab85048..af47672cb2cb 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -2025,28 +2025,28 @@ The following mount options are supported: gid= Set the group authorized to learn processes information. subset= Show only the specified subset of procfs. -hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories -(default). - -hidepid=1 means users may not access any /proc/<pid>/ directories but their -own. Sensitive files like cmdline, sched*, status are now protected against -other users. This makes it impossible to learn whether any user runs -specific program (given the program doesn't reveal itself by its behaviour). -As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users, -poorly written programs passing sensitive information via program arguments are -now protected against local eavesdroppers. - -hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other -users. It doesn't mean that it hides a fact whether a process with a specific -pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"), -but it hides process' uid and gid, which may be learned by stat()'ing -/proc/<pid>/ otherwise. It greatly complicates an intruder's task of gathering -information about running processes, whether some daemon runs with elevated -privileges, whether other user runs some sensitive program, whether other users -run any program at all, etc. - -hidepid=4 means that procfs should only contain /proc/<pid>/ directories -that the caller can ptrace. +hidepid=off or hidepid=0 means classic mode - everybody may access all +/proc/<pid>/ directories (default). + +hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/ +directories but their own. Sensitive files like cmdline, sched*, status are now +protected against other users. This makes it impossible to learn whether any +user runs specific program (given the program doesn't reveal itself by its +behaviour). As an additional bonus, as /proc/<pid>/cmdline is unaccessible for +other users, poorly written programs passing sensitive information via program +arguments are now protected against local eavesdroppers. + +hidepid=invisible or hidepid=2 means hidepid=noaccess plus all /proc/<pid>/ will +be fully invisible to other users. It doesn't mean that it hides a fact whether +a process with a specific pid value exists (it can be learned by other means, +e.g. by "kill -0 $PID"), but it hides process' uid and gid, which may be learned +by stat()'ing /proc/<pid>/ otherwise. It greatly complicates an intruder's task +of gathering information about running processes, whether some daemon runs with +elevated privileges, whether other user runs some sensitive program, whether +other users run any program at all, etc. + +hidepid=ptraceable or hidepid=4 means that procfs should only contain +/proc/<pid>/ directories that the caller can ptrace. gid= defines a group authorized to learn processes information otherwise prohibited by hidepid=. If you use some daemon like identd which needs to learn @@ -2093,8 +2093,8 @@ creates a new procfs instance. Mount options affect own procfs instance. It means that it became possible to have several procfs instances displaying tasks with different filtering options in one pid namespace. -# mount -o hidepid=2 -t proc proc /proc -# mount -o hidepid=1 -t proc proc /tmp/proc +# mount -o hidepid=invisible -t proc proc /proc +# mount -o hidepid=noaccess -t proc proc /tmp/proc # grep ^proc /proc/mounts -proc /proc proc rw,relatime,hidepid=2 0 0 -proc /tmp/proc proc rw,relatime,hidepid=1 0 0 +proc /proc proc rw,relatime,hidepid=invisible 0 0 +proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0 diff --git a/fs/proc/inode.c b/fs/proc/inode.c index e6577ce6027b..f01fb4bed75c 100644 --- a/fs/proc/inode.c +++ b/fs/proc/inode.c @@ -165,6 +165,17 @@ void proc_invalidate_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock deactivate_super(old_sb); } +static inline const char *hidepid2str(int v) +{ + switch (v) { + case HIDEPID_OFF: return "off"; + case HIDEPID_NO_ACCESS: return "noaccess"; + case HIDEPID_INVISIBLE: return "invisible"; + case HIDEPID_NOT_PTRACEABLE: return "ptraceable"; + } + BUG(); +} + static int proc_show_options(struct seq_file *seq, struct dentry *root) { struct proc_fs_info *fs_info = proc_sb_info(root->d_sb); @@ -172,7 +183,7 @@ static int proc_show_options(struct seq_file *seq, struct dentry *root) if (!gid_eq(fs_info->pid_gid, GLOBAL_ROOT_GID)) seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, fs_info->pid_gid)); if (fs_info->hide_pid != HIDEPID_OFF) - seq_printf(seq, ",hidepid=%u", fs_info->hide_pid); + seq_printf(seq, ",hidepid=%s", hidepid2str(fs_info->hide_pid)); if (fs_info->pidonly != PROC_PIDONLY_OFF) seq_printf(seq, ",subset=pid"); diff --git a/fs/proc/root.c b/fs/proc/root.c index dbcd96f07c7a..ba782d6e6197 100644 --- a/fs/proc/root.c +++ b/fs/proc/root.c @@ -45,7 +45,7 @@ enum proc_param { static const struct fs_parameter_spec proc_fs_parameters[] = { fsparam_u32("gid", Opt_gid), - fsparam_u32("hidepid", Opt_hidepid), + fsparam_string("hidepid", Opt_hidepid), fsparam_string("subset", Opt_subset), {} }; @@ -58,6 +58,35 @@ static inline int valid_hidepid(unsigned int value) value == HIDEPID_NOT_PTRACEABLE); } +static int proc_parse_hidepid_param(struct fs_context *fc, struct fs_parameter *param) +{ + struct proc_fs_context *ctx = fc->fs_private; + struct fs_parameter_spec hidepid_u32_spec = fsparam_u32("hidepid", Opt_hidepid); + struct fs_parse_result result; + int base = (unsigned long)hidepid_u32_spec.data; + + if (param->type != fs_value_is_string) + return invalf(fc, "proc: unexpected type of hidepid value\n"); + + if (!kstrtouint(param->string, base, &result.uint_32)) { + ctx->hidepid = result.uint_32; + return 0; + } + + if (!strcmp(param->string, "off")) + ctx->hidepid = HIDEPID_OFF; + else if (!strcmp(param->string, "noaccess")) + ctx->hidepid = HIDEPID_NO_ACCESS; + else if (!strcmp(param->string, "invisible")) + ctx->hidepid = HIDEPID_INVISIBLE; + else if (!strcmp(param->string, "ptraceable")) + ctx->hidepid = HIDEPID_NOT_PTRACEABLE; + else + return invalf(fc, "proc: unknown value of hidepid - %s\n", param->string); + + return 0; +} + static int proc_parse_subset_param(struct fs_context *fc, char *value) { struct proc_fs_context *ctx = fc->fs_private; @@ -97,9 +126,10 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param) break; case Opt_hidepid: - if (!valid_hidepid(result.uint_32)) + if (proc_parse_hidepid_param(fc, param)) + return -EINVAL; + if (!valid_hidepid(ctx->hidepid)) return invalf(fc, "proc: unknown value of hidepid.\n"); - ctx->hidepid = result.uint_32; break; case Opt_subset: