[PATCH 5.15 155/206] net: Add locking to protect skb->dev access in ip_output

Greg Kroah-Hartman
2026-02-04T15:00:07Z

From: Sharath Chandra Vurukala <quic_sharathv@quicinc.com>

commit 1dbf1d590d10a6d1978e8184f8dfe20af22d680a upstream.

In ip_output() skb->dev is updated from the skb_dst(skb)->dev
this can become invalid when the interface is unregistered and freed,

Introduced new skb_dst_dev_rcu() function to be used instead of
skb_dst_dev() within rcu_locks in ip_output.This will ensure that
all the skb's associated with the dev being deregistered will
be transnmitted out first, before freeing the dev.

Given that ip_output() is called within an rcu_read_lock()
critical section or from a bottom-half context, it is safe to introduce
an RCU read-side critical section within it.

Multiple panic call stacks were observed when UL traffic was run
in concurrency with device deregistration from different functions,
pasting one sample for reference.

[496733.627565][T13385] Call trace:
[496733.627570][T13385] bpf_prog_ce7c9180c3b128ea_cgroupskb_egres+0x24c/0x7f0
[496733.627581][T13385] __cgroup_bpf_run_filter_skb+0x128/0x498
[496733.627595][T13385] ip_finish_output+0xa4/0xf4
[496733.627605][T13385] ip_output+0x100/0x1a0
[496733.627613][T13385] ip_send_skb+0x68/0x100
[496733.627618][T13385] udp_send_skb+0x1c4/0x384
[496733.627625][T13385] udp_sendmsg+0x7b0/0x898
[496733.627631][T13385] inet_sendmsg+0x5c/0x7c
[496733.627639][T13385] __sys_sendto+0x174/0x1e4
[496733.627647][T13385] __arm64_sys_sendto+0x28/0x3c
[496733.627653][T13385] invoke_syscall+0x58/0x11c
[496733.627662][T13385] el0_svc_common+0x88/0xf4
[496733.627669][T13385] do_el0_svc+0x2c/0xb0
[496733.627676][T13385] el0_svc+0x2c/0xa4
[496733.627683][T13385] el0t_64_sync_handler+0x68/0xb4
[496733.627689][T13385] el0t_64_sync+0x1a4/0x1a8

Changes in v3:
- Replaced WARN_ON() with WARN_ON_ONCE(), as suggested by Willem de Bruijn.
- Dropped legacy lines mistakenly pulled in from an outdated branch.

Changes in v2:
- Addressed review comments from Eric Dumazet
- Used READ_ONCE() to prevent potential load/store tearing
- Added skb_dst_dev_rcu() and used along with rcu_read_lock() in ip_output

Signed-off-by: Sharath Chandra Vurukala <quic_sharathv@quicinc.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250730105118.GA26100@hu-sharathv-hyd.qualcomm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ Keerthana: Backported the patch to v5.15-v6.1 ]
Signed-off-by: Keerthana K <keerthana.kalyanasundaram@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/net/dst.h | 12 ++++++++++++
net/ipv4/ip_output.c | 16 +++++++++++-----
2 files changed, 23 insertions(+), 5 deletions(-)

--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -554,6 +554,18 @@ static inline void skb_dst_update_pmtu_n
dst->ops->update_pmtu(dst, NULL, skb, mtu, false);
}

+static inline struct net_device *dst_dev_rcu(const struct dst_entry *dst)
+{
+ /* In the future, use rcu_dereference(dst->dev) */
+ WARN_ON_ONCE(!rcu_read_lock_held());
+ return READ_ONCE(dst->dev);
+}
+
+static inline struct net_device *skb_dst_dev_rcu(const struct sk_buff *skb)
+{
+ return dst_dev_rcu(skb_dst(skb));
+}
+
struct dst_entry *dst_blackhole_check(struct dst_entry *dst, u32 cookie);
void dst_blackhole_update_pmtu(struct dst_entry *dst, struct sock *sk,
struct sk_buff *skb, u32 mtu, bool confirm_neigh);
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -420,17 +420,23 @@ int ip_mc_output(struct net *net, struct

int ip_output(struct net *net, struct sock *sk, struct sk_buff *skb)
{
- struct net_device *dev = skb_dst(skb)->dev, *indev = skb->dev;
+ struct net_device *dev, *indev = skb->dev;
+ int ret_val;
+
+ rcu_read_lock();
+ dev = skb_dst_dev_rcu(skb);

IP_UPD_PO_STATS(net, IPSTATS_MIB_OUT, skb->len);

skb->dev = dev;
skb->protocol = htons(ETH_P_IP);

- return NF_HOOK_COND(NFPROTO_IPV4, NF_INET_POST_ROUTING,
- net, sk, skb, indev, dev,
- ip_finish_output,
- !(IPCB(skb)->flags & IPSKB_REROUTED));
+ ret_val = NF_HOOK_COND(NFPROTO_IPV4, NF_INET_POST_ROUTING,
+ net, sk, skb, indev, dev,
+ ip_finish_output,
+ !(IPCB(skb)->flags & IPSKB_REROUTED));
+ rcu_read_unlock();
+ return ret_val;
}
EXPORT_SYMBOL(ip_output);