[PATCH 6.1 12/55] apparmor: validate DFA start states are in bounds in unpack_pdb

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Massimiliano Pellizzer <massimiliano.pellizzer@canonical.com>

commit 9063d7e2615f4a7ab321de6b520e23d370e58816 upstream.

Backport for conflicts caused by
ad596ea74e74 ("apparmor: group dfa policydb unpacking") which rearrange
and consolidated the unpack.

Start states are read from untrusted data and used as indexes into the
DFA state tables. The aa_dfa_next() function call in unpack_pdb() will
access dfa->tables[YYTD_ID_BASE][start], and if the start state exceeds
the number of states in the DFA, this results in an out-of-bound read.

==================================================================
 BUG: KASAN: slab-out-of-bounds in aa_dfa_next+0x2a1/0x360
 Read of size 4 at addr ffff88811956fb90 by task su/1097
 ...

Reject policies with out-of-bounds start states during unpacking
to prevent the issue.

Fixes: ad5ff3db53c6 ("AppArmor: Add ability to load extended policy")
Reported-by: Qualys Security Advisory <qsa@qualys.com>
Tested-by: Salvatore Bonaccorso <carnil@debian.org>
Reviewed-by: Georgia Garcia <georgia.garcia@canonical.com>
Reviewed-by: Cengiz Can <cengiz.can@canonical.com>
Signed-off-by: Massimiliano Pellizzer <massimiliano.pellizzer@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 security/apparmor/policy_unpack.c |   21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

--- a/security/apparmor/policy_unpack.c
+++ b/security/apparmor/policy_unpack.c
@@ -824,9 +824,18 @@ static struct aa_profile *unpack_profile
 			error = -EPROTO;
 			goto fail;
 		}
-		if (!aa_unpack_u32(e, &profile->policy.start[0], "start"))
+		if (!aa_unpack_u32(e, &profile->policy.start[0], "start")) {
 			/* default start state */
 			profile->policy.start[0] = DFA_START;
+		} else {
+			size_t state_count = profile->policy.dfa->tables[YYTD_ID_BASE]->td_lolen;
+
+			if (profile->policy.start[0] >= state_count) {
+				info = "invalid dfa start state";
+				goto fail;
+			}
+		}
+
 		/* setup class index */
 		for (i = AA_CLASS_FILE; i <= AA_CLASS_LAST; i++) {
 			profile->policy.start[i] =
@@ -847,9 +856,17 @@ static struct aa_profile *unpack_profile
 		info = "failed to unpack profile file rules";
 		goto fail;
 	} else if (profile->file.dfa) {
-		if (!aa_unpack_u32(e, &profile->file.start, "dfa_start"))
+		if (!aa_unpack_u32(e, &profile->file.start, "dfa_start")) {
 			/* default start state */
 			profile->file.start = DFA_START;
+		} else {
+			size_t state_count = profile->file.dfa->tables[YYTD_ID_BASE]->td_lolen;
+
+			if (profile->file.start >= state_count) {
+				info = "invalid dfa start state";
+				goto fail;
+			}
+		}
 	} else if (profile->policy.dfa &&
 		   profile->policy.start[AA_CLASS_FILE]) {
 		profile->file.dfa = aa_get_dfa(profile->policy.dfa);