[PATCH 5.10 226/491] icmp: fix NULL pointer dereference in icmp_tag_validation()

Greg Kroah-Hartman
2026-04-13T16:52:20Z

From: Weiming Shi <bestswngs@gmail.com>

[ Upstream commit 614aefe56af8e13331e50220c936fc0689cf5675 ]

icmp_tag_validation() unconditionally dereferences the result of
rcu_dereference(inet_protos[proto]) without checking for NULL.
The inet_protos[] array is sparse -- only about 15 of 256 protocol
numbers have registered handlers. When ip_no_pmtu_disc is set to 3
(hardened PMTU mode) and the kernel receives an ICMP Fragmentation
Needed error with a quoted inner IP header containing an unregistered
protocol number, the NULL dereference causes a kernel panic in
softirq context.

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
RIP: 0010:icmp_unreach (net/ipv4/icmp.c:1085 net/ipv4/icmp.c:1143)
Call Trace:
<IRQ>
icmp_rcv (net/ipv4/icmp.c:1527)
ip_protocol_deliver_rcu (net/ipv4/ip_input.c:207)
ip_local_deliver_finish (net/ipv4/ip_input.c:242)
ip_local_deliver (net/ipv4/ip_input.c:262)
ip_rcv (net/ipv4/ip_input.c:573)
__netif_receive_skb_one_core (net/core/dev.c:6164)
process_backlog (net/core/dev.c:6628)
handle_softirqs (kernel/softirq.c:561)
</IRQ>

Add a NULL check before accessing icmp_strict_tag_validation. If the
protocol has no registered handler, return false since it cannot
perform strict tag validation.

Fixes: 8ed1dc44d3e9 ("ipv4: introduce hardened ip_no_pmtu_disc mode")
Reported-by: Xiang Mei <xmei5@asu.edu>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Link: https://patch.msgid.link/20260318130558.1050247-4-bestswngs@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv4/icmp.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index efeeed4f0517e..3c74fecce2382 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -844,10 +844,12 @@ static void icmp_socket_deliver(struct sk_buff *skb, u32 info)

static bool icmp_tag_validation(int proto)
{
+ const struct net_protocol *ipprot;
bool ok;

rcu_read_lock();
- ok = rcu_dereference(inet_protos[proto])->icmp_strict_tag_validation;
+ ipprot = rcu_dereference(inet_protos[proto]);
+ ok = ipprot ? ipprot->icmp_strict_tag_validation : false;
rcu_read_unlock();
return ok;
}
--
2.51.0