net: fix secpath kmemleak

Mike Kazantsev found 3.5 kernels and beyond were leaking memory,
and tracked the faulty commit to a1c7fff7e18f59e ("net:
netdev_alloc_skb() use build_skb()")

While this commit seems fine, it uncovered a bug introduced
in commit bad43ca8325 ("net: introduce skb_try_coalesce()), in function
kfree_skb_partial()"):

If head is stolen, we free the sk_buff,
without removing references on secpath (skb->sp).

So IPsec + IP defrag/reassembly (using skb coalescing), or
TCP coalescing could leak secpath objects.

Fix this bug by calling skb_release_head_state(skb) to properly
release all possible references to linked objects.

Reported-by: Mike Kazantsev <mk.fraggod@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Bisected-by: Mike Kazantsev <mk.fraggod@gmail.com>
Tested-by: Mike Kazantsev <mk.fraggod@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 6e04b1fa11f2..4007c1437fda 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3379,10 +3379,12 @@ EXPORT_SYMBOL(__skb_warn_lro_forwarding);
 
 void kfree_skb_partial(struct sk_buff *skb, bool head_stolen)
 {
-        if (head_stolen)
+        if (head_stolen) {
+                skb_release_head_state(skb);
                 kmem_cache_free(skbuff_head_cache, skb);
-        else
+        } else {
                 __kfree_skb(skb);
+        }
 }
 EXPORT_SYMBOL(kfree_skb_partial);