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net_sched: fix datalen for ematch

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syzbot reported an out-of-bound access in em_nbyte. As initially
analyzed by Eric, this is because em_nbyte sets its own em->datalen
in em_nbyte_change() other than the one specified by user, but this
value gets overwritten later by its caller tcf_em_validate().
We should leave em->datalen untouched to respect their choices.

I audit all the in-tree ematch users, all of those implement
->change() set em->datalen, so we can just avoid setting it twice
in this case.

Reported-and-tested-by: syzbot+5af9a90dad568aa9f611@syzkaller.appspotmail.com
Reported-by: syzbot+2f07903a5b05e7f36410@syzkaller.appspotmail.com
Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Cong Wang 2020-01-22 15:42:02 -08:00 committed by David S. Miller
parent 42c9bdae23
commit 61678d28d4
1 changed files with 1 additions and 1 deletions
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2
net/sched/ematch.c
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@ -263,12 +263,12 @@ static int tcf_em_validate(struct tcf_proto *tp,
}
em->data = (unsigned long) v;
}
em->datalen = data_len;
}
}
em->matchid = em_hdr->matchid;
em->flags = em_hdr->flags;
em->datalen = data_len;
em->net = net;
err = 0;