diff options
| author | Eric Dumazet <edumazet@google.com> | 2026-01-18 15:29:41 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2026-02-06 16:44:09 +0100 |
| commit | 2619499169fb1c2ac4974b0f2d87767fb543582b (patch) | |
| tree | c918bcc1808d6cbc4bff9895da8238f89239ebea /net/ipv6 | |
| parent | accc3f8266d2a49881dbcf78c459477f4efa0ff3 (diff) | |
ipv6: annotate data-race in ndisc_router_discovery()
[ Upstream commit 9a063f96d87efc3a6cc667f8de096a3d38d74bb5 ]
syzbot found that ndisc_router_discovery() could read and write
in6_dev->ra_mtu without holding a lock [1]
This looks fine, IFLA_INET6_RA_MTU is best effort.
Add READ_ONCE()/WRITE_ONCE() to document the race.
Note that we might also reject illegal MTU values
(mtu < IPV6_MIN_MTU || mtu > skb->dev->mtu) in a future patch.
[1]
BUG: KCSAN: data-race in ndisc_router_discovery / ndisc_router_discovery
read to 0xffff888119809c20 of 4 bytes by task 25817 on cpu 1:
ndisc_router_discovery+0x151d/0x1c90 net/ipv6/ndisc.c:1558
ndisc_rcv+0x2ad/0x3d0 net/ipv6/ndisc.c:1841
icmpv6_rcv+0xe5a/0x12f0 net/ipv6/icmp.c:989
ip6_protocol_deliver_rcu+0xb2a/0x10d0 net/ipv6/ip6_input.c:438
ip6_input_finish+0xf0/0x1d0 net/ipv6/ip6_input.c:489
NF_HOOK include/linux/netfilter.h:318 [inline]
ip6_input+0x5e/0x140 net/ipv6/ip6_input.c:500
ip6_mc_input+0x27c/0x470 net/ipv6/ip6_input.c:590
dst_input include/net/dst.h:474 [inline]
ip6_rcv_finish+0x336/0x340 net/ipv6/ip6_input.c:79
...
write to 0xffff888119809c20 of 4 bytes by task 25816 on cpu 0:
ndisc_router_discovery+0x155a/0x1c90 net/ipv6/ndisc.c:1559
ndisc_rcv+0x2ad/0x3d0 net/ipv6/ndisc.c:1841
icmpv6_rcv+0xe5a/0x12f0 net/ipv6/icmp.c:989
ip6_protocol_deliver_rcu+0xb2a/0x10d0 net/ipv6/ip6_input.c:438
ip6_input_finish+0xf0/0x1d0 net/ipv6/ip6_input.c:489
NF_HOOK include/linux/netfilter.h:318 [inline]
ip6_input+0x5e/0x140 net/ipv6/ip6_input.c:500
ip6_mc_input+0x27c/0x470 net/ipv6/ip6_input.c:590
dst_input include/net/dst.h:474 [inline]
ip6_rcv_finish+0x336/0x340 net/ipv6/ip6_input.c:79
...
value changed: 0x00000000 -> 0xe5400659
Fixes: 49b99da2c9ce ("ipv6: add IFLA_INET6_RA_MTU to expose mtu value")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Rocco Yue <rocco.yue@mediatek.com>
Link: https://patch.msgid.link/20260118152941.2563857-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'net/ipv6')
| -rw-r--r-- | net/ipv6/ndisc.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c index 1a6408a24d21..affbf12d44f5 100644 --- a/net/ipv6/ndisc.c +++ b/net/ipv6/ndisc.c @@ -1572,8 +1572,8 @@ skip_routeinfo: memcpy(&n, ((u8 *)(ndopts.nd_opts_mtu+1))+2, sizeof(mtu)); mtu = ntohl(n); - if (in6_dev->ra_mtu != mtu) { - in6_dev->ra_mtu = mtu; + if (READ_ONCE(in6_dev->ra_mtu) != mtu) { + WRITE_ONCE(in6_dev->ra_mtu, mtu); send_ifinfo_notify = true; } |