When the forward output route cannot be used in icmp_route_lookup(), it enters the "reverse path" and calls ip_route_input() on fl4_dec.daddr, the original packet's source address. ip_route_input() only returns an error for truly invalid packets. For unreachable addresses it will succeed and return an input route whose dst.output is set to ip_rt_bug(). The existing check only rejects RTN_LOCAL routes, so the RTN_UNREACHABLE route types can still be returned and later used for output, syzkaller triggering a WARN_ON_ONCE() in ip_rt_bug() as bellow: ------------[ cut here ]------------ WARNING: net/ipv4/route.c:1273 at ip_rt_bug+0x14/0x20 RIP: 0010:ip_rt_bug+0x14/0x20 Call Trace: ip_push_pending_frames+0xfa/0x100 __icmp_send+0x905/0xf10 ip_options_compile+0xc0/0xd0 ip_rcv_finish_core+0x321/0xae0 ip_rcv+0x1de/0x260 __netif_receive_skb_one_core+0x11a/0x130 netif_receive_skb+0x7b/0x260 tun_get_user+0x11bf/0x1c10 ------------[ cut here ]------------ Reject input route that is RTN_UNREACHABLE to fix it. The net warning is only printed for RTN_LOCAL, as RTN_UNREACHABLE is not the result of a race condition. Fixes: 8b7817f3a959 ("[IPSEC]: Add ICMP host relookup support") Suggested-by: Ido Schimmel Reviewed-by: Jiayuan Chen Signed-off-by: Dong Chenchen --- v2: - RTN_UNICAST judgement will reject bforward packet. Only reject RTN_UNREACHABLE v3: - RTN_UNREACHABLE dont need warn log. v4: - Modify the comments and commit msg to make them more accurate. --- net/ipv4/icmp.c | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c index 0caedfc7ca92..288da11c5de8 100644 --- a/net/ipv4/icmp.c +++ b/net/ipv4/icmp.c @@ -581,16 +581,17 @@ static struct rtable *icmp_route_lookup(struct net *net, struct flowi4 *fl4, skb_dstref_restore(skb_in, orefdst); /* - * At this point, fl4_dec.daddr should NOT be local (we - * checked fl4_dec.saddr above). However, a race condition - * may occur if the address is added to the interface - * concurrently. In that case, ip_route_input() returns a - * LOCAL route with dst.output=ip_rt_bug, which must not - * be used for output. + * fl4_dec.daddr is not expected to be local here, but it can be added to + * an interface concurrently, in which case ip_route_input() returns a + * LOCAL route. It can also fail to build a forwarding route towards + * fl4_dec.daddr, for example, when forwarding is disabled, and return an + * UNREACHABLE route. Both cases will result in a route with + * dst.output=ip_rt_bug, which must not be used for output. */ - if (!err && rt2 && rt2->rt_type == RTN_LOCAL) { - net_warn_ratelimited("detected local route for %pI4 during ICMP sending, src %pI4\n", - &fl4_dec.daddr, &fl4_dec.saddr); + if (!err && rt2 && (rt2->rt_type == RTN_LOCAL || rt2->rt_type == RTN_UNREACHABLE)) { + if (rt2->rt_type == RTN_LOCAL) + net_warn_ratelimited("detected local route for %pI4 during ICMP sending, src %pI4\n", + &fl4_dec.daddr, &fl4_dec.saddr); dst_release(&rt2->dst); err = -EINVAL; } -- 2.25.1