[apparmor] [PATCH] apparmor: fix null pointer deref in find_attach when xmatch is null

[Ryan Lee]

I just realized that I forgot to add sign off on my patch, so I'm
resending it with the Signed-off-by line added.

On Wed, Aug 21, 2024 at 11:12 AM Ryan Lee <ryan.lee at canonical.com> wrote:
>
> After further analysis, the root cause turned out to be the xmatch not
> being set up properly when allocating a null profile for learning in
> complain mode. Thus, I am withdrawing the above patch and instead
> attaching a new patch that does this setup in aa_alloc_null.
>
> Ryan
>
> On Mon, Aug 19, 2024 at 1:05 PM Ryan Lee <ryan.lee at canonical.com> wrote:
> >
> > find_attach loops over profile entries and first checks for a DFA, falling
> > back onto a strcmp otherwise. However, the check if (attach->xmatch->dfa)
> > did not account for the possibility that (attach->xmatch) could be null.
> > This occured with a sequence of profile replacements that resulted in a
> > kernel BUG print due to the null pointer dereference.
> >
> > To avoid this issue, first check that (attach->xmatch) is not null.
> >
> > The one-line patch is attached to the email.
> >
> > Ryan
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