linux-kernel - [PATCH 3.16 38/72] sch_netem: fix a divide by zero in tabledist()

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Message-ID: <lsq.1575813165.194100818@decadent.org.uk>
Date:   Sun, 08 Dec 2019 13:53:22 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Jakub Kicinski" <jakub.kicinski@...ronome.com>,
        "Eric Dumazet" <edumazet@...gle.com>,
        "syzbot" <syzkaller@...glegroups.com>
Subject: [PATCH 3.16 38/72] sch_netem: fix a divide by zero in tabledist()

3.16.79-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Eric Dumazet <edumazet@...gle.com>

commit b41d936b5ecfdb3a4abc525ce6402a6c49cffddc upstream.

syzbot managed to crash the kernel in tabledist() loading
an empty distribution table.

	t = dist->table[rnd % dist->size];

Simply return an error when such load is attempted.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: syzbot <syzkaller@...glegroups.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/sched/sch_netem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -737,7 +737,7 @@ static int get_dist_table(struct Qdisc *
 	int i;
 	size_t s;
 
-	if (n > NETEM_DIST_MAX)
+	if (!n || n > NETEM_DIST_MAX)
 		return -EINVAL;
 
 	s = sizeof(struct disttable) + n * sizeof(s16);