diff options
| author | Weiming Shi <bestswngs@gmail.com> | 2026-06-17 14:55:13 +0800 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2026-06-21 15:13:24 -0700 |
| commit | d186e942365acece7c56d39da05dd63bf95b280a (patch) | |
| tree | 30f6849d632c37457ac0fb88cca182e1a41647c9 | |
| parent | 27ccb68e7cccead5d8c611665a45d23032d468b3 (diff) | |
ipv6: ndisc: fix NULL deref in accept_untracked_na()
accept_untracked_na() re-fetches the inet6_dev with __in6_dev_get(dev)
and dereferences idev->cnf.accept_untracked_na without a NULL check,
even though its only caller ndisc_recv_na() already fetched and
NULL-checked idev for the same device.
Both reads of dev->ip6_ptr run in the same RCU read-side critical
section, but a concurrent addrconf_ifdown() can clear dev->ip6_ptr
between them: lowering the MTU below IPV6_MIN_MTU calls addrconf_ifdown()
without the synchronize_net() that orders the unregister path, so the
re-fetch returns NULL and oopses:
BUG: KASAN: null-ptr-deref in ndisc_recv_na (net/ipv6/ndisc.c:974)
Read of size 4 at addr 0000000000000364
Call Trace:
<IRQ>
ndisc_recv_na (net/ipv6/ndisc.c:974)
icmpv6_rcv (net/ipv6/icmp.c:1193)
ip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:479)
ip6_input_finish (net/ipv6/ip6_input.c:534)
ip6_input (net/ipv6/ip6_input.c:545)
ip6_mc_input (net/ipv6/ip6_input.c:635)
ipv6_rcv (net/ipv6/ip6_input.c:351)
</IRQ>
It is reachable by an unprivileged user via a network namespace.
Pass the caller's already validated idev instead of re-fetching it; the
idev stays alive for the whole RCU critical section, so it is safe even
after dev->ip6_ptr has been cleared.
Fixes: aaa5f515b16b ("net: ipv6: new accept_untracked_na option to accept na only if in-network")
Reported-by: Xiang Mei <xmei5@asu.edu>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Link: https://patch.msgid.link/20260617065512.2529757-2-bestswngs@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
| -rw-r--r-- | net/ipv6/ndisc.c | 8 |
1 files changed, 3 insertions, 5 deletions
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c index e7ad13c5bd26..f867ec8d3d90 100644 --- a/net/ipv6/ndisc.c +++ b/net/ipv6/ndisc.c @@ -967,10 +967,8 @@ out: return reason; } -static int accept_untracked_na(struct net_device *dev, struct in6_addr *saddr) +static int accept_untracked_na(struct inet6_dev *idev, struct in6_addr *saddr) { - struct inet6_dev *idev = __in6_dev_get(dev); - switch (READ_ONCE(idev->cnf.accept_untracked_na)) { case 0: /* Don't accept untracked na (absent in neighbor cache) */ return 0; @@ -980,7 +978,7 @@ static int accept_untracked_na(struct net_device *dev, struct in6_addr *saddr) * same subnet as an address configured on the interface that * received the na */ - return !!ipv6_chk_prefix(saddr, dev); + return !!ipv6_chk_prefix(saddr, idev->dev); default: return 0; } @@ -1078,7 +1076,7 @@ static enum skb_drop_reason ndisc_recv_na(struct sk_buff *skb) */ new_state = msg->icmph.icmp6_solicited ? NUD_REACHABLE : NUD_STALE; if (!neigh && lladdr && idev && READ_ONCE(idev->cnf.forwarding)) { - if (accept_untracked_na(dev, saddr)) { + if (accept_untracked_na(idev, saddr)) { neigh = neigh_create(&nd_tbl, &msg->target, dev); new_state = NUD_STALE; } |