FAILED: patch "[PATCH] ipv6: rpl: fix NULL dereference of idev in ipv6_rpl_srh_rcv()" failed to apply to 6.12-stable tree

PATCH New [email protected] 2 participants 3 messages Sep 3 – Sep 8

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Networking Stable branch IPv4/IPv6

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[email protected]

author maintainer

2026-09-03 14:24 UTC #0 lore raw

The patch below does not apply to the 6.12-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 <[email protected]>.

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-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x f826df95332c07380206dbd54178b6eefb311aba
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090349-gone-tricky-59ac@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From f826df95332c07380206dbd54178b6eefb311aba Mon Sep 17 00:00:00 2001
From: Andrea Mayer <[email protected]>
Date: Mon, 17 Aug 2026 15:26:44 +0200
Subject: [PATCH] ipv6: rpl: fix NULL dereference of idev in ipv6_rpl_srh_rcv()

ipv6_rpl_srh_rcv() dereferences idev from __in6_dev_get() without a NULL check when reading idev->cnf.rpl_seg_enabled.

When the device's MTU drops below IPV6_MIN_MTU, addrconf_ifdown() clears dev->ip6_ptr through RCU_INIT_POINTER(). A packet that passed the idev check in ip6_rcv_core() can then reach ipv6_rpl_srh_rcv() with dev->ip6_ptr already NULL.

Reproduced by flooding the receiving interface with ping6 traffic while flapping its MTU between 1500 and 1200:

 BUG: KASAN: null-ptr-deref in ipv6_rpl_srh_rcv+0xb3/0x1070
 Read of size 4 at addr 00000000000006b4 by task ping6/394

 CPU: 2 UID: 0 PID: 394 Comm: ping6 Not tainted 7.2.0-rc7-micro-vm-dev-00095-g24ef02f934ee #240 PREEMPT(full)
 Call Trace:
  <IRQ>
  kasan_report+0xc6/0x100
  ipv6_rpl_srh_rcv+0xb3/0x1070
  ip6_protocol_deliver_rcu+0x759/0x9a0
  ip6_input_finish+0xa8/0x1b0
  ip6_input+0xe1/0x490
  ipv6_rcv+0x33d/0x460
  __netif_receive_skb_one_core+0xd6/0x130
  process_backlog+0x2cc/0xa00
  __napi_poll.constprop.0+0x56/0x270
  net_rx_action+0x327/0x730
  handle_softirqs+0x11e/0x630
  do_softirq+0xb3/0xf0
  </IRQ>

Both ipv6_rpl_srh_rcv() and ipv6_srh_rcv() are called only from ipv6_rthdr_rcv(), which already has an idev lookup.

Fix the NULL dereference on the RPL path by checking idev in ipv6_rthdr_rcv(), before it calls either function. The callees take idev as an argument and no longer call __in6_dev_get(), so the packet is now dropped in one place, with SKB_DROP_REASON_IPV6DISABLED on both paths.

Fixes 8610c7c6e3bd ("net: ipv6: add support for rpl sr exthdr")

Cc [email protected]

Signed-off-by Andrea Mayer <[email protected]>

Tested-by Xiang Mei <[email protected]>

Reviewed-by Simon Horman <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Jakub Kicinski <[email protected]>

net/ipv6/exthdrs.c +12 ~~-14~~

index 9c677eb1d1a6..51941ad656a3 100644
@@ -368,23 +368,16 @@ static void seg6_update_csum(struct sk_buff *skb)
 			   (__be32 *)addr);
 }
 
-static int ipv6_srh_rcv(struct sk_buff *skb)
+static int ipv6_srh_rcv(struct sk_buff *skb, struct inet6_dev *idev)
 {
 	struct inet6_skb_parm *opt = IP6CB(skb);
 	struct net *net = dev_net(skb->dev);
 	struct ipv6_sr_hdr *hdr;
-	struct inet6_dev *idev;
 	struct in6_addr *addr;
 	int accept_seg6;
 
 	hdr = (struct ipv6_sr_hdr *)skb_transport_header(skb);
 
-	idev = __in6_dev_get(skb->dev);
-	if (!idev) {
-		kfree_skb(skb);
-		return -1;
-	}
-
 	accept_seg6 = min(READ_ONCE(net->ipv6.devconf_all->seg6_enabled),
 			  READ_ONCE(idev->cnf.seg6_enabled));

@@ -485,12 +478,11 @@ static int ipv6_srh_rcv(struct sk_buff *skb)
 	return -1;
 }
 
-static int ipv6_rpl_srh_rcv(struct sk_buff *skb)
+static int ipv6_rpl_srh_rcv(struct sk_buff *skb, struct inet6_dev *idev)
 {
 	struct ipv6_rpl_sr_hdr *hdr, *ohdr, *chdr;
 	struct inet6_skb_parm *opt = IP6CB(skb);
 	struct net *net = dev_net(skb->dev);
-	struct inet6_dev *idev;
 	struct ipv6hdr *oldhdr;
 	unsigned int chdr_len;
 	unsigned char *buf;

@@ -499,8 +491,6 @@ static int ipv6_rpl_srh_rcv(struct sk_buff *skb)
 	u64 n = 0;
 	u32 r;
 
-	idev = __in6_dev_get(skb->dev);
-
 	accept_rpl_seg = min(READ_ONCE(net->ipv6.devconf_all->rpl_seg_enabled),
 			     READ_ONCE(idev->cnf.rpl_seg_enabled));
 	if (!accept_rpl_seg) {

@@ -689,10 +679,14 @@ static int ipv6_rthdr_rcv(struct sk_buff *skb)
 	switch (hdr->type) {
 	case IPV6_SRCRT_TYPE_4:
 		/* segment routing */
-		return ipv6_srh_rcv(skb);
+		if (!idev)
+			goto disabled;
+		return ipv6_srh_rcv(skb, idev);
 	case IPV6_SRCRT_TYPE_3:
 		/* rpl segment routing */
-		return ipv6_rpl_srh_rcv(skb);
+		if (!idev)
+			goto disabled;
+		return ipv6_rpl_srh_rcv(skb, idev);
 	default:
 		break;
 	}

@@ -837,6 +831,10 @@ static int ipv6_rthdr_rcv(struct sk_buff *skb)
 	icmpv6_param_prob(skb, ICMPV6_HDR_FIELD,
 			  (&hdr->type) - skb_network_header(skb));
 	return -1;
+
+disabled:
+	kfree_skb_reason(skb, SKB_DROP_REASON_IPV6DISABLED);
+	return -1;
 }
 
 static const struct inet6_protocol rthdr_protocol = {

Sasha Levin

maintainer

2026-09-08 16:21 UTC #1 lore raw

PATCH 1/2 ipv6: annotate data-races around devconf->rpl_seg_enabled

From: Yue Haibing <[email protected]>

[ Upstream commit 3a5f55500f3e93cf4d62351c753452279b088b4b ]

devconf->rpl_seg_enabled can be changed concurrently from /proc/sys/net/ipv6/conf, annotate lockless reads on it.

Signed-off-by Yue Haibing <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Jakub Kicinski <[email protected]>

Stable-dep-of: f826df95332c ("ipv6: rpl: fix NULL dereference of idev in ipv6_rpl_srh_rcv()")

Signed-off-by Sasha Levin <[email protected]>

---
 net/ipv6/exthdrs.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

net/ipv6/exthdrs.c +2 -4

index e91afe5ec0b5d..e1e64e5507d22 100644
@@ -504,10 +504,8 @@ static int ipv6_rpl_srh_rcv(struct sk_buff *skb)
 
 	idev = __in6_dev_get(skb->dev);
 
-	accept_rpl_seg = net->ipv6.devconf_all->rpl_seg_enabled;
-	if (accept_rpl_seg > idev->cnf.rpl_seg_enabled)
-		accept_rpl_seg = idev->cnf.rpl_seg_enabled;
-
+	accept_rpl_seg = min(READ_ONCE(net->ipv6.devconf_all->rpl_seg_enabled),
+			     READ_ONCE(idev->cnf.rpl_seg_enabled));
 	if (!accept_rpl_seg) {
 		kfree_skb(skb);
 		return -1;

Signature · 1 line

2.53.0

Sasha Levin

maintainer

2026-09-08 16:21 UTC #2 lore raw

PATCH 2/2 ipv6: rpl: fix NULL dereference of idev in ipv6_rpl_srh_rcv()

From: Andrea Mayer <[email protected]>

[ Upstream commit f826df95332c07380206dbd54178b6eefb311aba ]

ipv6_rpl_srh_rcv() dereferences idev from __in6_dev_get() without a NULL check when reading idev->cnf.rpl_seg_enabled.

Reproduced by flooding the receiving interface with ping6 traffic while flapping its MTU between 1500 and 1200:

 BUG: KASAN: null-ptr-deref in ipv6_rpl_srh_rcv+0xb3/0x1070
 Read of size 4 at addr 00000000000006b4 by task ping6/394

 CPU: 2 UID: 0 PID: 394 Comm: ping6 Not tainted 7.2.0-rc7-micro-vm-dev-00095-g24ef02f934ee #240 PREEMPT(full)
 Call Trace:
  <IRQ>
  kasan_report+0xc6/0x100
  ipv6_rpl_srh_rcv+0xb3/0x1070
  ip6_protocol_deliver_rcu+0x759/0x9a0
  ip6_input_finish+0xa8/0x1b0
  ip6_input+0xe1/0x490
  ipv6_rcv+0x33d/0x460
  __netif_receive_skb_one_core+0xd6/0x130
  process_backlog+0x2cc/0xa00
  __napi_poll.constprop.0+0x56/0x270
  net_rx_action+0x327/0x730
  handle_softirqs+0x11e/0x630
  do_softirq+0xb3/0xf0
  </IRQ>

Both ipv6_rpl_srh_rcv() and ipv6_srh_rcv() are called only from ipv6_rthdr_rcv(), which already has an idev lookup.

Fixes 8610c7c6e3bd ("net: ipv6: add support for rpl sr exthdr")

Cc [email protected]

Signed-off-by Andrea Mayer <[email protected]>

Tested-by Xiang Mei <[email protected]>

Reviewed-by Simon Horman <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Jakub Kicinski <[email protected]>

Signed-off-by Sasha Levin <[email protected]>

---
 net/ipv6/exthdrs.c | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

net/ipv6/exthdrs.c +12 ~~-14~~

index e1e64e5507d22..d7f053b684c11 100644
@@ -371,23 +371,16 @@ static void seg6_update_csum(struct sk_buff *skb)
 			   (__be32 *)addr);
 }
 
-static int ipv6_srh_rcv(struct sk_buff *skb)
+static int ipv6_srh_rcv(struct sk_buff *skb, struct inet6_dev *idev)
 {
 	struct inet6_skb_parm *opt = IP6CB(skb);
 	struct net *net = dev_net(skb->dev);
 	struct ipv6_sr_hdr *hdr;
-	struct inet6_dev *idev;
 	struct in6_addr *addr;
 	int accept_seg6;
 
 	hdr = (struct ipv6_sr_hdr *)skb_transport_header(skb);
 
-	idev = __in6_dev_get(skb->dev);
-	if (!idev) {
-		kfree_skb(skb);
-		return -1;
-	}
-
 	accept_seg6 = min(READ_ONCE(net->ipv6.devconf_all->seg6_enabled),
 			  READ_ONCE(idev->cnf.seg6_enabled));

@@ -488,12 +481,11 @@ static int ipv6_srh_rcv(struct sk_buff *skb)
 	return -1;
 }
 
-static int ipv6_rpl_srh_rcv(struct sk_buff *skb)
+static int ipv6_rpl_srh_rcv(struct sk_buff *skb, struct inet6_dev *idev)
 {
 	struct ipv6_rpl_sr_hdr *hdr, *ohdr, *chdr;
 	struct inet6_skb_parm *opt = IP6CB(skb);
 	struct net *net = dev_net(skb->dev);
-	struct inet6_dev *idev;
 	struct ipv6hdr *oldhdr;
 	unsigned int chdr_len;
 	unsigned char *buf;

@@ -502,8 +494,6 @@ static int ipv6_rpl_srh_rcv(struct sk_buff *skb)
 	u64 n = 0;
 	u32 r;
 
-	idev = __in6_dev_get(skb->dev);
-
 	accept_rpl_seg = min(READ_ONCE(net->ipv6.devconf_all->rpl_seg_enabled),
 			     READ_ONCE(idev->cnf.rpl_seg_enabled));
 	if (!accept_rpl_seg) {

@@ -692,10 +682,14 @@ static int ipv6_rthdr_rcv(struct sk_buff *skb)
 	switch (hdr->type) {
 	case IPV6_SRCRT_TYPE_4:
 		/* segment routing */
-		return ipv6_srh_rcv(skb);
+		if (!idev)
+			goto disabled;
+		return ipv6_srh_rcv(skb, idev);
 	case IPV6_SRCRT_TYPE_3:
 		/* rpl segment routing */
-		return ipv6_rpl_srh_rcv(skb);
+		if (!idev)
+			goto disabled;
+		return ipv6_rpl_srh_rcv(skb, idev);
 	default:
 		break;
 	}

@@ -840,6 +834,10 @@ static int ipv6_rthdr_rcv(struct sk_buff *skb)
 	icmpv6_param_prob(skb, ICMPV6_HDR_FIELD,
 			  (&hdr->type) - skb_network_header(skb));
 	return -1;
+
+disabled:
+	kfree_skb_reason(skb, SKB_DROP_REASON_IPV6DISABLED);
+	return -1;
 }
 
 static const struct inet6_protocol rthdr_protocol = {

Signature · 1 line

2.53.0