[PATCH 1/1] net: fix secpath kmemleak

[Colin King]

From: Eric Dumazet <edumazet at google.com>

BugLink: https://bugs.launchpad.net/bugs/1065434

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 at gmail.com>
Signed-off-by: Eric Dumazet <edumazet at google.com>
Bisected-by: Mike Kazantsev <mk.fraggod at gmail.com>
Tested-by: Mike Kazantsev <mk.fraggod at gmail.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit 3d861f661006606bf159fd6bd973e8)
Signed-off-by: Colin Ian King <colin.king at canonical.com>
---
 net/core/skbuff.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 6e04b1f..4007c14 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);
 
-- 
1.7.9.5