netdev - [PATCH AUTOSEL 4.9 19/19] sch_netem: fix a divide by zero in tabledist()

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Date:   Tue,  1 Oct 2019 12:45:05 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Eric Dumazet <edumazet@...gle.com>,
        syzbot <syzkaller@...glegroups.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Sasha Levin <sashal@...nel.org>, netdev@...r.kernel.org
Subject: [PATCH AUTOSEL 4.9 19/19] sch_netem: fix a divide by zero in tabledist()

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

[ Upstream commit b41d936b5ecfdb3a4abc525ce6402a6c49cffddc ]

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: Sasha Levin <sashal@...nel.org>
---
 net/sched/sch_netem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index e9812e21dbc9b..12e3ae09c4ba1 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -711,7 +711,7 @@ static int get_dist_table(struct Qdisc *sch, const struct nlattr *attr)
 	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);
-- 
2.20.1