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AppArmor: Fix underflow in xindex calculation

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If the xindex value stored in the accept tables is 0, the extraction of
that value will result in an underflow (0 - 4).

In properly compiled policy this should not happen for file rules but
it may be possible for other rule types in the future.

To exploit this underflow a user would have to be able to load a corrupt
policy, which requires CAP_MAC_ADMIN, overwrite system policy in kernel
memory or know of a compiler error resulting in the flaw being present
for loaded policy (no such flaw is known at this time).

Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Kees Cook <kees@ubuntu.com>
This commit is contained in:
John Johansen 2012-02-22 00:32:30 -08:00
parent ade3ddc01e
commit 8b964eae20
1 changed files with 1 additions and 1 deletions
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2
security/apparmor/include/file.h
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@ -117,7 +117,7 @@ static inline u16 dfa_map_xindex(u16 mask)
index |= AA_X_NAME;
} else if (old_index == 3) {
index |= AA_X_NAME | AA_X_CHILD;
} else {
} else if (old_index) {
index |= AA_X_TABLE;
index |= old_index - 4;
}