[PATCH net] net: really orphan skbs tied to closing sk

[PATCH net] net: really orphan skbs tied to closing sk

[Paolo Abeni]

If the owing socket is shutting down - e.g. the sock reference
count already dropped to 0 and only sk_wmem_alloc is keeping
the sock alive, skb_orphan_partial() becomes a no-op.

When forwarding packets over veth with GRO enabled, the above
causes refcount errors.

This change addresses the issue with a plain skb_orphan() call
in the critical scenario.

Fixes: 9adc89af724f ("net: let skb_orphan_partial wake-up waiters.")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 include/net/sock.h | 4 +++-
 net/core/sock.c    | 8 ++++----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 42bc5e1a627f..0e962d8bc73b 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2231,13 +2231,15 @@ static inline void skb_set_owner_r(struct sk_buff *skb, struct sock *sk)
 	sk_mem_charge(sk, skb->truesize);
 }
 
-static inline void skb_set_owner_sk_safe(struct sk_buff *skb, struct sock *sk)
+static inline __must_check bool skb_set_owner_sk_safe(struct sk_buff *skb, struct sock *sk)
 {
 	if (sk && refcount_inc_not_zero(&sk->sk_refcnt)) {
 		skb_orphan(skb);
 		skb->destructor = sock_efree;
 		skb->sk = sk;
+		return true;
 	}
+	return false;
 }
 
 void sk_reset_timer(struct sock *sk, struct timer_list *timer,
diff --git a/net/core/sock.c b/net/core/sock.c
index c761c4a0b66b..958614ea16ed 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2132,10 +2132,10 @@ void skb_orphan_partial(struct sk_buff *skb)
 	if (skb_is_tcp_pure_ack(skb))
 		return;
 
-	if (can_skb_orphan_partial(skb))
-		skb_set_owner_sk_safe(skb, skb->sk);
-	else
-		skb_orphan(skb);
+	if (can_skb_orphan_partial(skb) && skb_set_owner_sk_safe(skb, skb->sk))
+		return;
+
+	skb_orphan(skb);
 }
 EXPORT_SYMBOL(skb_orphan_partial);
 
-- 
2.26.2

Re: [PATCH net] net: really orphan skbs tied to closing sk

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Tue, 11 May 2021 10:35:21 +0200 you wrote:
> If the owing socket is shutting down - e.g. the sock reference
> count already dropped to 0 and only sk_wmem_alloc is keeping
> the sock alive, skb_orphan_partial() becomes a no-op.
> 
> When forwarding packets over veth with GRO enabled, the above
> causes refcount errors.
> 
> [...]

Here is the summary with links:
  - [net] net: really orphan skbs tied to closing sk
    https://git.kernel.org/netdev/net/c/098116e7e640

You are awesome, thank you!
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