FAILED: patch "[PATCH] ipv6: ioam: add NULL check for idev in ipv6_hop_ioam()" failed to apply to 5.15-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x d4ea0dfd75011b78cebf3808f98ac4c4f51a6fb9
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026052814-waggle-aerospace-72c0@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d4ea0dfd75011b78cebf3808f98ac4c4f51a6fb9 Mon Sep 17 00:00:00 2001
From: Justin Iurman <justin.iurman@gmail.com>
Date: Sun, 17 May 2026 20:30:59 +0200
Subject: [PATCH] ipv6: ioam: add NULL check for idev in ipv6_hop_ioam()

Reported by Sashiko:

The function ipv6_hop_ioam() accesses
__in6_dev_get(skb->dev)->cnf.ioam6_enabled without validating the returned
idev pointer. Because addrconf_ifdown() can concurrently clear dev->ip6_ptr
via RCU, __in6_dev_get() can return NULL during interface teardown, which
could cause a NULL pointer dereference when processing an IOAM Hop-by-Hop
option.

Let's add a check and use SKB_DROP_REASON_IPV6DISABLED accordingly.

Fixes: 9ee11f0fff20 ("ipv6: ioam: Data plane support for Pre-allocated Trace")
Cc: stable@vger.kernel.org
Signed-off-by: Justin Iurman <justin.iurman@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260517183059.29140-1-justin.iurman@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
index 03cbce842c1a..47c5502a34a2 100644
--- a/net/ipv6/exthdrs.c
+++ b/net/ipv6/exthdrs.c
@@ -910,16 +910,27 @@ static bool ipv6_hop_ra(struct sk_buff *skb, int optoff)
 
 static bool ipv6_hop_ioam(struct sk_buff *skb, int optoff)
 {
+	enum skb_drop_reason drop_reason;
 	struct ioam6_trace_hdr *trace;
 	struct ioam6_namespace *ns;
+	struct inet6_dev *idev;
 	struct ioam6_hdr *hdr;
 
+	drop_reason = SKB_DROP_REASON_IP_INHDR;
+
 	/* Bad alignment (must be 4n-aligned) */
 	if (optoff & 3)
 		goto drop;
 
+	/* Does the device still have IPv6 configuration? */
+	idev = __in6_dev_get(skb->dev);
+	if (!idev) {
+		drop_reason = SKB_DROP_REASON_IPV6DISABLED;
+		goto drop;
+	}
+
 	/* Ignore if IOAM is not enabled on ingress */
-	if (!READ_ONCE(__in6_dev_get(skb->dev)->cnf.ioam6_enabled))
+	if (!READ_ONCE(idev->cnf.ioam6_enabled))
 		goto ignore;
 
 	/* Truncated Option header */
@@ -972,7 +983,7 @@ static bool ipv6_hop_ioam(struct sk_buff *skb, int optoff)
 	return true;
 
 drop:
-	kfree_skb_reason(skb, SKB_DROP_REASON_IP_INHDR);
+	kfree_skb_reason(skb, drop_reason);
 	return false;
 }