[PATCH 6.1 277/481] ipv6: use RCU in ip6_xmit()

Greg Kroah-Hartman
2026-03-23T16:21:49Z

6.1-stable review patch. If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@google.com>

commit 9085e56501d93af9f2d7bd16f7fcfacdde47b99c upstream.

Use RCU in ip6_xmit() in order to use dst_dev_rcu() to prevent
possible UAF.

Fixes: 4a6ce2b6f2ec ("net: introduce a new function dst_dev_put()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20250828195823.3958522-4-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Keerthana K <keerthana.kalyanasundaram@broadcom.com>
Signed-off-by: Shivani Agarwal <shivani.agarwal@broadcom.com>
---
net/ipv6/ip6_output.c | 35 +++++++++++++++++++++--------------
1 file changed, 21 insertions(+), 14 deletions(-)

--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -258,35 +258,36 @@ bool ip6_autoflowlabel(struct net *net,
int ip6_xmit(const struct sock *sk, struct sk_buff *skb, struct flowi6 *fl6,
__u32 mark, struct ipv6_txoptions *opt, int tclass, u32 priority)
{
- struct net *net = sock_net(sk);
const struct ipv6_pinfo *np = inet6_sk(sk);
struct in6_addr *first_hop = &fl6->daddr;
struct dst_entry *dst = skb_dst(skb);
- struct net_device *dev = dst->dev;
struct inet6_dev *idev = ip6_dst_idev(dst);
struct hop_jumbo_hdr *hop_jumbo;
int hoplen = sizeof(*hop_jumbo);
+ struct net *net = sock_net(sk);
unsigned int head_room;
+ struct net_device *dev;
struct ipv6hdr *hdr;
u8 proto = fl6->flowi6_proto;
int seg_len = skb->len;
- int hlimit = -1;
+ int ret, hlimit = -1;
u32 mtu;

+ rcu_read_lock();
+
+ dev = dst_dev_rcu(dst);
head_room = sizeof(struct ipv6hdr) + hoplen + LL_RESERVED_SPACE(dev);
if (opt)
head_room += opt->opt_nflen + opt->opt_flen;

if (unlikely(head_room > skb_headroom(skb))) {
- /* Make sure idev stays alive */
- rcu_read_lock();
+ /* idev stays alive while we hold rcu_read_lock(). */
skb = skb_expand_head(skb, head_room);
if (!skb) {
IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTDISCARDS);
- rcu_read_unlock();
- return -ENOBUFS;
+ ret = -ENOBUFS;
+ goto unlock;
}
- rcu_read_unlock();
}

if (opt) {
@@ -348,17 +349,21 @@ int ip6_xmit(const struct sock *sk, stru
* skb to its handler for processing
*/
skb = l3mdev_ip6_out((struct sock *)sk, skb);
- if (unlikely(!skb))
- return 0;
+ if (unlikely(!skb)) {
+ ret = 0;
+ goto unlock;
+ }

/* hooks should never assume socket lock is held.
* we promote our socket to non const
*/
- return NF_HOOK(NFPROTO_IPV6, NF_INET_LOCAL_OUT,
- net, (struct sock *)sk, skb, NULL, dev,
- dst_output);
+ ret = NF_HOOK(NFPROTO_IPV6, NF_INET_LOCAL_OUT,
+ net, (struct sock *)sk, skb, NULL, dev,
+ dst_output);
+ goto unlock;
}

+ ret = -EMSGSIZE;
skb->dev = dev;
/* ipv6_local_error() does not require socket lock,
* we promote our socket to non const
@@ -367,7 +372,9 @@ int ip6_xmit(const struct sock *sk, stru

IP6_INC_STATS(net, idev, IPSTATS_MIB_FRAGFAILS);
kfree_skb(skb);
- return -EMSGSIZE;
+unlock:
+ rcu_read_unlock();
+ return ret;
}
EXPORT_SYMBOL(ip6_xmit);