linux-kernel - [PATCH] apparmor: fix off-by-one comparison on MAXMAPPED

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Message-ID: <b6efd4c2-e572-748a-848b-d714af3deedc@canonical.com>
Date:   Wed, 8 Nov 2017 08:09:52 -0800
From:   John Johansen <john.johansen@...onical.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     LKLM <linux-kernel@...r.kernel.org>,
        Colin Ian King <colin.king@...onical.com>
Subject: [PATCH] apparmor: fix off-by-one comparison on MAXMAPPED_SIG

This came in yesterday, and I have verified our regression tests
were missing this and it can cause an oops. Please apply.

There is a an off-by-one comparision on sig against MAXMAPPED_SIG
that can lead to a read outside the sig_map array if sig
is MAXMAPPED_SIG. Fix this.

Verified that the check is an out of bounds case that can cause an oops.

Revised: add comparison fix to second case
Fixes: cd1dbf76b23d ("apparmor: add the ability to mediate signals")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
Signed-off-by: John Johansen <john.johansen@...onical.com>
---
 security/apparmor/ipc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/security/apparmor/ipc.c b/security/apparmor/ipc.c
index 66fb9ede9447..7ca0032e7ba9 100644
--- a/security/apparmor/ipc.c
+++ b/security/apparmor/ipc.c
@@ -128,7 +128,7 @@ static inline int map_signal_num(int sig)
 		return SIGUNKNOWN;
 	else if (sig >= SIGRTMIN)
 		return sig - SIGRTMIN + 128;	/* rt sigs mapped to 128 */
-	else if (sig <= MAXMAPPED_SIG)
+	else if (sig < MAXMAPPED_SIG)
 		return sig_map[sig];
 	return SIGUNKNOWN;
 }
@@ -163,7 +163,7 @@ static void audit_signal_cb(struct audit_buffer *ab, void *va)
 			audit_signal_mask(ab, aad(sa)->denied);
 		}
 	}
-	if (aad(sa)->signal <= MAXMAPPED_SIG)
+	if (aad(sa)->signal < MAXMAPPED_SIG)
 		audit_log_format(ab, " signal=%s", sig_names[aad(sa)->signal]);
 	else
 		audit_log_format(ab, " signal=rtmin+%d",
-- 
2.11.0