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

[Ryan Lee]

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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