From 2c87d63ac853550e734edfd45e1be5e5aa44fbcc Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Mon, 14 Aug 2017 00:52:58 +0200 Subject: [PATCH] ipv4: route: fix inet_rtm_getroute induced crash "ip route get $daddr iif eth0 from $saddr" causes: BUG: KASAN: use-after-free in ip_route_input_rcu+0x1535/0x1b50 Call Trace: ip_route_input_rcu+0x1535/0x1b50 ip_route_input_noref+0xf9/0x190 tcp_v4_early_demux+0x1a4/0x2b0 ip_rcv+0xbcb/0xc05 __netif_receive_skb+0x9c/0xd0 netif_receive_skb_internal+0x5a8/0x890 Problem is that inet_rtm_getroute calls either ip_route_input_rcu (if an iif was provided) or ip_route_output_key_hash_rcu. But ip_route_input_rcu, unlike ip_route_output_key_hash_rcu, already associates the dst_entry with the skb. This clears the SKB_DST_NOREF bit (i.e. skb_dst_drop will release/free the entry while it should not). Thus only set the dst if we called ip_route_output_key_hash_rcu(). I tested this patch by running: while true;do ip r get 10.0.1.2;done > /dev/null & while true;do ip r get 10.0.1.2 iif eth0 from 10.0.1.1;done > /dev/null & ... and saw no crash or memory leak. Cc: Roopa Prabhu Cc: David Ahern Fixes: ba52d61e0ff ("ipv4: route: restore skb_dst_set in inet_rtm_getroute") Signed-off-by: Florian Westphal Acked-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/route.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/ipv4/route.c b/net/ipv4/route.c index 0383e66f59bc..7effa62beed3 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -2750,12 +2750,13 @@ static int inet_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh, err = 0; if (IS_ERR(rt)) err = PTR_ERR(rt); + else + skb_dst_set(skb, &rt->dst); } if (err) goto errout_free; - skb_dst_set(skb, &rt->dst); if (rtm->rtm_flags & RTM_F_NOTIFY) rt->rt_flags |= RTCF_NOTIFY;