linux-kernel - [net] ipv6: sr: fix missing sk_buff release in seg6_input

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Date: Fri, 17 May 2024 18:45:41 +0200
From: Andrea Mayer <andrea.mayer@...roma2.it>
To: "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        David Lebrun <david.lebrun@...ouvain.be>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc: Stefano Salsano <stefano.salsano@...roma2.it>,
        Paolo Lungaroni <paolo.lungaroni@...roma2.it>,
        Ahmed Abdelsalam <ahabdels.dev@...il.com>,
        Andrea Mayer <andrea.mayer@...roma2.it>
Subject: [net] ipv6: sr: fix missing sk_buff release in seg6_input_core

The seg6_input() function is responsible for adding the SRH into a
packet, delegating the operation to the seg6_input_core(). This function
uses the skb_cow_head() to ensure that there is sufficient headroom in
the sk_buff for accommodating the link-layer header.
In the event that the skb_cow_header() function fails, the
seg6_input_core() catches the error but it does not release the sk_buff,
which will result in a memory leak.

This issue was introduced in commit af3b5158b89d ("ipv6: sr: fix BUG due
to headroom too small after SRH push") and persists even after commit
7a3f5b0de364 ("netfilter: add netfilter hooks to SRv6 data plane"),
where the entire seg6_input() code was refactored to deal with netfilter
hooks.

The proposed patch addresses the identified memory leak by requiring the
seg6_input_core() function to release the sk_buff in the event that
skb_cow_head() fails.

Fixes: af3b5158b89d ("ipv6: sr: fix BUG due to headroom too small after SRH push")
Signed-off-by: Andrea Mayer <andrea.mayer@...roma2.it>
---
 net/ipv6/seg6_iptunnel.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c
index 03b877ff4558..a75df2ec8db0 100644
--- a/net/ipv6/seg6_iptunnel.c
+++ b/net/ipv6/seg6_iptunnel.c
@@ -459,10 +459,8 @@ static int seg6_input_core(struct net *net, struct sock *sk,
 	int err;

 	err = seg6_do_srh(skb);
-	if (unlikely(err)) {
-		kfree_skb(skb);
-		return err;
-	}
+	if (unlikely(err))
+		goto drop;

 	slwt = seg6_lwt_lwtunnel(orig_dst->lwtstate);

@@ -486,7 +484,7 @@ static int seg6_input_core(struct net *net, struct sock *sk,

 	err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
 	if (unlikely(err))
-		return err;
+		goto drop;

 	if (static_branch_unlikely(&nf_hooks_lwtunnel_enabled))
 		return NF_HOOK(NFPROTO_IPV6, NF_INET_LOCAL_OUT,
@@ -494,6 +492,9 @@ static int seg6_input_core(struct net *net, struct sock *sk,
 			       skb_dst(skb)->dev, seg6_input_finish);

 	return seg6_input_finish(dev_net(skb->dev), NULL, skb);
+drop:
+	kfree_skb(skb);
+	return err;
 }

 static int seg6_input_nf(struct sk_buff *skb)
-- 
2.20.1