Merge branch 'ipv6-fix-possible-uaf-in-output-paths'

Eric Dumazet says:

====================
ipv6: fix possible UAF in output paths

First patch fixes an issue spotted by syzbot, and the two
other patches fix error paths after skb_expand_head()
adoption.
====================

Link: https://patch.msgid.link/20240820160859.3786976-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv6/ip6_output.c

@@ -70,11 +70,15 @@ static int ip6_finish_output2(struct net *net, struct sock *sk, struct sk_buff *
 
 	/* Be paranoid, rather than too clever. */
 	if (unlikely(hh_len > skb_headroom(skb)) && dev->header_ops) {
+		/* Make sure idev stays alive */
+		rcu_read_lock();
 		skb = skb_expand_head(skb, hh_len);
 		if (!skb) {
 			IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTDISCARDS);
+			rcu_read_unlock();
 			return -ENOMEM;
 		}
+		rcu_read_unlock();
 	}
 
 	hdr = ipv6_hdr(skb);
@@ -283,11 +287,15 @@ int ip6_xmit(const struct sock *sk, struct sk_buff *skb, struct flowi6 *fl6,
 		head_room += opt->opt_nflen + opt->opt_flen;
 
 	if (unlikely(head_room > skb_headroom(skb))) {
+		/* Make sure idev stays alive */
+		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;
 		}
+		rcu_read_unlock();
 	}
 
 	if (opt) {
@@ -1956,6 +1964,7 @@ int ip6_send_skb(struct sk_buff *skb)
 	struct rt6_info *rt = dst_rt6_info(skb_dst(skb));
 	int err;
 
+	rcu_read_lock();
 	err = ip6_local_out(net, skb->sk, skb);
 	if (err) {
 		if (err > 0)
@@ -1965,6 +1974,7 @@ int ip6_send_skb(struct sk_buff *skb)
 				      IPSTATS_MIB_OUTDISCARDS);
 	}
 
+	rcu_read_unlock();
 	return err;
 }