From: Cong Wang <xiyou.wangcong@gmail.com> [ Upstream commit 61678d28d4a45ef376f5d02a839cc37509ae9281 ] 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: 1da177e4c3f4 ("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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com> --- net/sched/ematch.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/sched/ematch.c b/net/sched/ematch.c index 1331a4c..750d88d 100644 --- a/net/sched/ematch.c +++ b/net/sched/ematch.c @@ -267,12 +267,12 @@ 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; -- 1.8.3