[SRU][F/J/L][PATCH 1/1] ipv4: fix null-deref in ipv4_link_failure

[Yuxuan Luo]

From: Kyle Zeng <zengyhkyle at gmail.com>

Currently, we assume the skb is associated with a device before calling
__ip_options_compile, which is not always the case if it is re-routed by
ipvs.
When skb->dev is NULL, dev_net(skb->dev) will become null-dereference.
This patch adds a check for the edge case and switch to use the net_device
from the rtable when skb->dev is NULL.

Fixes: ed0de45a1008 ("ipv4: recompile ip options in ipv4_link_failure")
Suggested-by: David Ahern <dsahern at kernel.org>
Signed-off-by: Kyle Zeng <zengyhkyle at gmail.com>
Cc: Stephen Suryaputra <ssuryaextr at gmail.com>
Cc: Vadim Fedorenko <vfedorenko at novek.ru>
Reviewed-by: David Ahern <dsahern at kernel.org>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit 0113d9c9d1ccc07f5a3710dac4aa24b6d711278c)
CVE-2023-42754
Signed-off-by: Yuxuan Luo <yuxuan.luo at canonical.com>
---
 net/ipv4/route.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 435def2c74b59..34c5996d41c31 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1221,6 +1221,7 @@ static struct dst_entry *ipv4_dst_check(struct dst_entry *dst, u32 cookie)
 
 static void ipv4_send_dest_unreach(struct sk_buff *skb)
 {
+	struct net_device *dev;
 	struct ip_options opt;
 	int res;
 
@@ -1238,7 +1239,8 @@ static void ipv4_send_dest_unreach(struct sk_buff *skb)
 		opt.optlen = ip_hdr(skb)->ihl * 4 - sizeof(struct iphdr);
 
 		rcu_read_lock();
-		res = __ip_options_compile(dev_net(skb->dev), &opt, skb, NULL);
+		dev = skb->dev ? skb->dev : skb_rtable(skb)->dst.dev;
+		res = __ip_options_compile(dev_net(dev), &opt, skb, NULL);
 		rcu_read_unlock();
 
 		if (res)
-- 
2.34.1