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Subject[PATCH 4.14 36/45] ipv6: fix uninit-value in ip6_multipath_l3_keys()
4.14-stable review patch.  If anyone has any objections, please let me know.


From: Eric Dumazet <>

[ Upstream commit cea67a2dd6b2419dcc13a39309b9a79a1f773193 ]

syzbot/KMSAN reported an uninit-value in ip6_multipath_l3_keys(),
root caused to a bad assumption of ICMP header being already
pulled in skb->head

ip_multipath_l3_keys() does the correct thing, so it is an IPv6 only bug.

BUG: KMSAN: uninit-value in ip6_multipath_l3_keys net/ipv6/route.c:1830 [inline]
BUG: KMSAN: uninit-value in rt6_multipath_hash+0x5c4/0x640 net/ipv6/route.c:1858
CPU: 0 PID: 4507 Comm: syz-executor661 Not tainted 4.16.0+ #87
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x185/0x1d0 lib/dump_stack.c:53
kmsan_report+0x142/0x240 mm/kmsan/kmsan.c:1067
__msan_warning_32+0x6c/0xb0 mm/kmsan/kmsan_instr.c:683
ip6_multipath_l3_keys net/ipv6/route.c:1830 [inline]
rt6_multipath_hash+0x5c4/0x640 net/ipv6/route.c:1858
ip6_route_input+0x65a/0x920 net/ipv6/route.c:1884
ip6_rcv_finish+0x413/0x6e0 net/ipv6/ip6_input.c:69
NF_HOOK include/linux/netfilter.h:288 [inline]
ipv6_rcv+0x1e16/0x2340 net/ipv6/ip6_input.c:208
__netif_receive_skb_core+0x47df/0x4a90 net/core/dev.c:4562
__netif_receive_skb net/core/dev.c:4627 [inline]
netif_receive_skb_internal+0x49d/0x630 net/core/dev.c:4701
netif_receive_skb+0x230/0x240 net/core/dev.c:4725
tun_rx_batched drivers/net/tun.c:1555 [inline]
tun_get_user+0x740f/0x7c60 drivers/net/tun.c:1962
tun_chr_write_iter+0x1d4/0x330 drivers/net/tun.c:1990
call_write_iter include/linux/fs.h:1782 [inline]
new_sync_write fs/read_write.c:469 [inline]
__vfs_write+0x7fb/0x9f0 fs/read_write.c:482
vfs_write+0x463/0x8d0 fs/read_write.c:544
SYSC_write+0x172/0x360 fs/read_write.c:589
SyS_write+0x55/0x80 fs/read_write.c:581
do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287

Fixes: 23aebdacb05d ("ipv6: Compute multipath hash for ICMP errors from offending packet")
Signed-off-by: Eric Dumazet <>
Reported-by: syzbot <>
Cc: Jakub Sitnicki <>
Acked-by: Jakub Sitnicki <>
Signed-off-by: David S. Miller <>
Signed-off-by: Greg Kroah-Hartman <>
net/ipv6/route.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1222,11 +1222,16 @@ static void ip6_multipath_l3_keys(const
const struct ipv6hdr *inner_iph;
const struct icmp6hdr *icmph;
struct ipv6hdr _inner_iph;
+ struct icmp6hdr _icmph;

if (likely(outer_iph->nexthdr != IPPROTO_ICMPV6))
goto out;

- icmph = icmp6_hdr(skb);
+ icmph = skb_header_pointer(skb, skb_transport_offset(skb),
+ sizeof(_icmph), &_icmph);
+ if (!icmph)
+ goto out;
if (icmph->icmp6_type != ICMPV6_DEST_UNREACH &&
icmph->icmp6_type != ICMPV6_PKT_TOOBIG &&
icmph->icmp6_type != ICMPV6_TIME_EXCEED &&

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