audit: fix out-of-bounds read in audit_compare_dname_path

[PATCH] audit: fix out-of-bounds read in audit_compare_dname_path

Posted by Stanislav Fort 1 month ago

When a watch on dir=/ is combined with an fsnotify event for a
single-character name directly under / (e.g., creating /a), an
out-of-bounds read can occur in audit_compare_dname_path().

The helper parent_len() returns 1 for "/". In audit_compare_dname_path(),
when parentlen equals the full path length (1), the code sets p = path + 1
and pathlen = 1 - 1 = 0. The subsequent loop then dereferences
p[pathlen - 1] (i.e., p[-1]), causing an out-of-bounds read.

Fix this by adding a pathlen > 0 check to the while loop condition
to prevent the out-of-bounds access.

Reported-by: Stanislav Fort <disclosure@aisle.com>
Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Stanislav Fort <disclosure@aisle.com>
---
 kernel/auditfilter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
index e3f42018ed46..f7708fe2c457 100644
--- a/kernel/auditfilter.c
+++ b/kernel/auditfilter.c
@@ -1326,7 +1326,7 @@ int audit_compare_dname_path(const struct qstr *dname, const char *path, int par
 
 	/* handle trailing slashes */
 	pathlen -= parentlen;
-	while (p[pathlen - 1] == '/')
+	while (pathlen > 0 && p[pathlen - 1] == '/')
 		pathlen--;
 
 	if (pathlen != dlen)
-- 
2.39.3 (Apple Git-146)

Re: [PATCH] audit: fix out-of-bounds read in audit_compare_dname_path

Posted by Paul Moore 1 month ago

On Tue, Sep 2, 2025 at 7:00 AM Stanislav Fort <stanislav.fort@aisle.com> wrote:
>
> When a watch on dir=/ is combined with an fsnotify event for a
> single-character name directly under / (e.g., creating /a), an
> out-of-bounds read can occur in audit_compare_dname_path().
>
> The helper parent_len() returns 1 for "/". In audit_compare_dname_path(),
> when parentlen equals the full path length (1), the code sets p = path + 1
> and pathlen = 1 - 1 = 0. The subsequent loop then dereferences
> p[pathlen - 1] (i.e., p[-1]), causing an out-of-bounds read.
>
> Fix this by adding a pathlen > 0 check to the while loop condition
> to prevent the out-of-bounds access.
>
> Reported-by: Stanislav Fort <disclosure@aisle.com>
> Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
> Signed-off-by: Stanislav Fort <disclosure@aisle.com>
> ---
>  kernel/auditfilter.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Thanks Stanislav.  It looks like this problem was likely introduced in
e92eebb0d611 ("audit: fix suffixed '/' filename matching"), I'll add a
'Fixes:' and a stable tag.

I'm building a test kernel right now to test things, but did you
verify that the path matching fixed in e92eebb0d611 still works
correctly?

> diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
> index e3f42018ed46..f7708fe2c457 100644
> --- a/kernel/auditfilter.c
> +++ b/kernel/auditfilter.c
> @@ -1326,7 +1326,7 @@ int audit_compare_dname_path(const struct qstr *dname, const char *path, int par
>
>         /* handle trailing slashes */
>         pathlen -= parentlen;
> -       while (p[pathlen - 1] == '/')
> +       while (pathlen > 0 && p[pathlen - 1] == '/')
>                 pathlen--;
>
>         if (pathlen != dlen)
> --
> 2.39.3 (Apple Git-146)

-- 
paul-moore.com

Re: [PATCH] audit: fix out-of-bounds read in audit_compare_dname_path

Posted by Paul Moore 1 month ago

On Tue, Sep 2, 2025 at 2:50 PM Paul Moore <paul@paul-moore.com> wrote:
> On Tue, Sep 2, 2025 at 7:00 AM Stanislav Fort <stanislav.fort@aisle.com> wrote:
> >
> > When a watch on dir=/ is combined with an fsnotify event for a
> > single-character name directly under / (e.g., creating /a), an
> > out-of-bounds read can occur in audit_compare_dname_path().
> >
> > The helper parent_len() returns 1 for "/". In audit_compare_dname_path(),
> > when parentlen equals the full path length (1), the code sets p = path + 1
> > and pathlen = 1 - 1 = 0. The subsequent loop then dereferences
> > p[pathlen - 1] (i.e., p[-1]), causing an out-of-bounds read.
> >
> > Fix this by adding a pathlen > 0 check to the while loop condition
> > to prevent the out-of-bounds access.
> >
> > Reported-by: Stanislav Fort <disclosure@aisle.com>
> > Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
> > Signed-off-by: Stanislav Fort <disclosure@aisle.com>
> > ---
> >  kernel/auditfilter.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
>
> Thanks Stanislav.  It looks like this problem was likely introduced in
> e92eebb0d611 ("audit: fix suffixed '/' filename matching"), I'll add a
> 'Fixes:' and a stable tag.
>
> I'm building a test kernel right now to test things, but did you
> verify that the path matching fixed in e92eebb0d611 still works
> correctly?

The basic testing I've done today looks good.  If you can let me know
about the email in your sign-off we can get this merged and up to
Linus this week.

> > diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
> > index e3f42018ed46..f7708fe2c457 100644
> > --- a/kernel/auditfilter.c
> > +++ b/kernel/auditfilter.c
> > @@ -1326,7 +1326,7 @@ int audit_compare_dname_path(const struct qstr *dname, const char *path, int par
> >
> >         /* handle trailing slashes */
> >         pathlen -= parentlen;
> > -       while (p[pathlen - 1] == '/')
> > +       while (pathlen > 0 && p[pathlen - 1] == '/')
> >                 pathlen--;
> >
> >         if (pathlen != dlen)
> > --
> > 2.39.3 (Apple Git-146)

-- 
paul-moore.com

Re: [PATCH] audit: fix out-of-bounds read in audit_compare_dname_path

Posted by Paul Moore 1 month ago

On Tue, Sep 2, 2025 at 2:50 PM Paul Moore <paul@paul-moore.com> wrote:
> On Tue, Sep 2, 2025 at 7:00 AM Stanislav Fort <stanislav.fort@aisle.com> wrote:
> >
> > When a watch on dir=/ is combined with an fsnotify event for a
> > single-character name directly under / (e.g., creating /a), an
> > out-of-bounds read can occur in audit_compare_dname_path().
> >
> > The helper parent_len() returns 1 for "/". In audit_compare_dname_path(),
> > when parentlen equals the full path length (1), the code sets p = path + 1
> > and pathlen = 1 - 1 = 0. The subsequent loop then dereferences
> > p[pathlen - 1] (i.e., p[-1]), causing an out-of-bounds read.
> >
> > Fix this by adding a pathlen > 0 check to the while loop condition
> > to prevent the out-of-bounds access.
> >
> > Reported-by: Stanislav Fort <disclosure@aisle.com>
> > Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
> > Signed-off-by: Stanislav Fort <disclosure@aisle.com>

I also just noticed a disconnect on the email address.  I can leave
the Reported-by email as disclosure@, but do you mind if I convert
your Signed-off-by email to stanislav.fort@?

> > ---
> >  kernel/auditfilter.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
>
> Thanks Stanislav.  It looks like this problem was likely introduced in
> e92eebb0d611 ("audit: fix suffixed '/' filename matching"), I'll add a
> 'Fixes:' and a stable tag.
>
> I'm building a test kernel right now to test things, but did you
> verify that the path matching fixed in e92eebb0d611 still works
> correctly?
>
> > diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
> > index e3f42018ed46..f7708fe2c457 100644
> > --- a/kernel/auditfilter.c
> > +++ b/kernel/auditfilter.c
> > @@ -1326,7 +1326,7 @@ int audit_compare_dname_path(const struct qstr *dname, const char *path, int par
> >
> >         /* handle trailing slashes */
> >         pathlen -= parentlen;
> > -       while (p[pathlen - 1] == '/')
> > +       while (pathlen > 0 && p[pathlen - 1] == '/')
> >                 pathlen--;
> >
> >         if (pathlen != dlen)
> > --
> > 2.39.3 (Apple Git-146)

-- 
paul-moore.com

Re: [PATCH] audit: fix out-of-bounds read in audit_compare_dname_path

Posted by Paul Moore 4 weeks, 1 day ago

On Tue, Sep 2, 2025 at 2:52 PM Paul Moore <paul@paul-moore.com> wrote:
> On Tue, Sep 2, 2025 at 2:50 PM Paul Moore <paul@paul-moore.com> wrote:
> > On Tue, Sep 2, 2025 at 7:00 AM Stanislav Fort <stanislav.fort@aisle.com> wrote:
> > >
> > > When a watch on dir=/ is combined with an fsnotify event for a
> > > single-character name directly under / (e.g., creating /a), an
> > > out-of-bounds read can occur in audit_compare_dname_path().
> > >
> > > The helper parent_len() returns 1 for "/". In audit_compare_dname_path(),
> > > when parentlen equals the full path length (1), the code sets p = path + 1
> > > and pathlen = 1 - 1 = 0. The subsequent loop then dereferences
> > > p[pathlen - 1] (i.e., p[-1]), causing an out-of-bounds read.
> > >
> > > Fix this by adding a pathlen > 0 check to the while loop condition
> > > to prevent the out-of-bounds access.
> > >
> > > Reported-by: Stanislav Fort <disclosure@aisle.com>
> > > Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
> > > Signed-off-by: Stanislav Fort <disclosure@aisle.com>
>
> I also just noticed a disconnect on the email address.  I can leave
> the Reported-by email as disclosure@, but do you mind if I convert
> your Signed-off-by email to stanislav.fort@?

Stanislav, are you okay with changing your sign-off email to
stanislav.fort@aisle.com?

--
paul-moore.com

Re: [PATCH] audit: fix out-of-bounds read in audit_compare_dname_path

Posted by Disclosure 4 weeks, 1 day ago

Hi Paul,

Yes, please go ahead and change the Signed-off-by to:
Signed-off-by: Stanislav Fort <stanislav.fort@aisle.com>

Sorry for the slight delay and thanks for the quick review, testing, and 
for adding the Fixes tag.

Best wishes,
Stanislav Fort
Aisle Research

On Wednesday, September 3, 2025 at 6:16:59 PM UTC+3 Paul Moore wrote:

> On Tue, Sep 2, 2025 at 2:52 PM Paul Moore <paul@paul-moore.com> wrote:
> > On Tue, Sep 2, 2025 at 2:50 PM Paul Moore <paul@paul-moore.com> wrote:
> > > On Tue, Sep 2, 2025 at 7:00 AM Stanislav Fort <
> stanislav.fort@aisle.com> wrote:
> > > >
> > > > When a watch on dir=/ is combined with an fsnotify event for a
> > > > single-character name directly under / (e.g., creating /a), an
> > > > out-of-bounds read can occur in audit_compare_dname_path().
> > > >
> > > > The helper parent_len() returns 1 for "/". In 
> audit_compare_dname_path(),
> > > > when parentlen equals the full path length (1), the code sets p = 
> path + 1
> > > > and pathlen = 1 - 1 = 0. The subsequent loop then dereferences
> > > > p[pathlen - 1] (i.e., p[-1]), causing an out-of-bounds read.
> > > >
> > > > Fix this by adding a pathlen > 0 check to the while loop condition
> > > > to prevent the out-of-bounds access.
> > > >
> > > > Reported-by: Stanislav Fort <disclosure@aisle.com>
> > > > Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
> > > > Signed-off-by: Stanislav Fort <disclosure@aisle.com>
> >
> > I also just noticed a disconnect on the email address. I can leave
> > the Reported-by email as disclosure@, but do you mind if I convert
> > your Signed-off-by email to stanislav.fort@?
>
> Stanislav, are you okay with changing your sign-off email to
> stanislav.fort@aisle.com?
>
> --
> paul-moore.com
>

Re: [PATCH] audit: fix out-of-bounds read in audit_compare_dname_path

Posted by Paul Moore 4 weeks, 1 day ago

On Wed, Sep 3, 2025 at 2:03 PM Disclosure <disclosure@aisle.com> wrote:
>
> Hi Paul,
>
> Yes, please go ahead and change the Signed-off-by to:
> Signed-off-by: Stanislav Fort <stanislav.fort@aisle.com>
>
> Sorry for the slight delay and thanks for the quick review, testing, and for adding the Fixes tag.

No worries, thanks for the fix :)

I'm merging this into audit/stable-6.17 and I'll plan to send this up
to Linus later this week.

-- 
paul-moore.com