[PATCH 5.10.y] ipv6: raw: fix use-after-free in rawv6_send_hdrinc()

[Sasha Levin <sashal@kernel.org>]

From: Zhou Qiuyue <n0ps1edzz@gmail.com>

[ Upstream commit 66dfb2cacda7faae614d688943d85e75abf7f586 ]

rawv6_send_hdrinc() caches the route before handing the skb to
l3mdev_ip6_out(). The VRF output path may replace skb->dst and release
the original route, leaving the cached pointer stale.

The function later dereferences that pointer for statistics accounting
and as the output device passed to NF_HOOK(). Its RCU read-side critical
section starts after l3mdev_ip6_out(), so it cannot prevent the old route
from being reclaimed in between.

Reload the route from the current skb destination after
l3mdev_ip6_out() returns.

KASAN reports a slab-use-after-free in rawv6_sendmsg(), with the route
allocated by ip6_dst_alloc(), freed by dst_destroy() from rcu_core(), and
the related RCU callback queued from vrf_l3_out().

Fixes: 4c1feac58e06 ("net: vrf: Flip IPv6 output path from FIB lookup hook to out hook")
Cc: stable@vger.kernel.org
Signed-off-by: Zhou Qiuyue <n0ps1edzz@gmail.com>
Reviewed-by: Hangbin Liu <liuhangbin@kylinos.cn>
Signed-off-by: Dave Miller <davem@davem-thinkpadp1gen8.ibmlond.csb>
[ sashal: Replaced the unavailable dst_rt6_info() helper with a direct cast to struct rt6_info *. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/ipv6/raw.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index 6ec51b1a4e26b..e24e49cdf141c 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -650,6 +650,9 @@ static int rawv6_send_hdrinc(struct sock *sk, struct msghdr *msg, int length,
 	if (unlikely(!skb))
 		return 0;
 
+	/* l3mdev_ip6_out() may have replaced the skb dst. */
+	rt = (struct rt6_info *)skb_dst(skb);
+
 	/* Acquire rcu_read_lock() in case we need to use rt->rt6i_idev
 	 * in the error path. Since skb has been freed, the dst could
 	 * have been queued for deletion.
-- 
2.53.0