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

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Message-ID: <CAHC9VhQsmaGPM7+6HX9vqjPjG7fXwV+F19+U052qaT4DYrwnFA@mail.gmail.com>
Date: Tue, 2 Sep 2025 14:50:30 -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 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>
> ---
>  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