linux-kernel - Re: [PATCH] audit: fix out-of-bounds read in audit_compare_dname

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Message-ID: <CAHC9VhRtXzSGafaqLm_EDq=rj4BhDaOkaS0uJ89W-Scw2Zyxuw@mail.gmail.com>
Date: Tue, 2 Sep 2025 14:52:35 -0400
From: Paul Moore <paul@...l-moore.com>
To: Stanislav Fort <stanislav.fort@...le.com>
Cc: audit@...r.kernel.org, torvalds@...uxfoundation.org, eparis@...hat.com, 
	security@...nel.org, linux-kernel@...r.kernel.org, 
	Stanislav Fort <disclosure@...le.com>
Subject: Re: [PATCH] audit: fix out-of-bounds read in audit_compare_dname_path

On Tue, Sep 2, 2025 at 2:50 PM Paul Moore <paul@...l-moore.com> wrote:
> On Tue, Sep 2, 2025 at 7:00 AM Stanislav Fort <stanislav.fort@...le.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@...le.com>
> > Suggested-by: Linus Torvalds <torvalds@...uxfoundation.org>
> > Signed-off-by: Stanislav Fort <disclosure@...le.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