Commit e44699d2 authored Jun 29, 2017 by Michal Kubeček Committed by David S. Miller Jun 29, 2017

net: handle NAPI_GRO_FREE_STOLEN_HEAD case also in napi_frags_finish()

Recently I started seeing warnings about pages with refcount -1. The
problem was traced to packets being reused after their head was merged into
a GRO packet by skb_gro_receive(). While bisecting the issue pointed to
commit c21b48cc ("net: adjust skb->truesize in ___pskb_trim()") and
I have never seen it on a kernel with it reverted, I believe the real
problem appeared earlier when the option to merge head frag in GRO was
implemented.

Handling NAPI_GRO_FREE_STOLEN_HEAD state was only added to GRO_MERGED_FREE
branch of napi_skb_finish() so that if the driver uses napi_gro_frags()
and head is merged (which in my case happens after the skb_condense()
call added by the commit mentioned above), the skb is reused including the
head that has been merged. As a result, we release the page reference
twice and eventually end up with negative page refcount.

To fix the problem, handle NAPI_GRO_FREE_STOLEN_HEAD in napi_frags_finish()
the same way it's done in napi_skb_finish().

Fixes: d7e8883c ("net: make GRO aware of skb->head_frag")
Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 6bdf6abc

net/core/dev.c

+17 −7

Original line number	Diff line number	Diff line
		@@ -4767,6 +4767,13 @@ struct packet_offload *gro_find_complete_by_type(__be16 type)
		}
		EXPORT_SYMBOL(gro_find_complete_by_type);

		static void napi_skb_free_stolen_head(struct sk_buff *skb)
		{
		skb_dst_drop(skb);
		secpath_reset(skb);
		kmem_cache_free(skbuff_head_cache, skb);
		}

		static gro_result_t napi_skb_finish(gro_result_t ret, struct sk_buff *skb)
		{
		switch (ret) {
		@@ -4780,13 +4787,10 @@ static gro_result_t napi_skb_finish(gro_result_t ret, struct sk_buff *skb)
		break;

		case GRO_MERGED_FREE:
		if (NAPI_GRO_CB(skb)->free == NAPI_GRO_FREE_STOLEN_HEAD) {
		skb_dst_drop(skb);
		secpath_reset(skb);
		kmem_cache_free(skbuff_head_cache, skb);
		} else {
		if (NAPI_GRO_CB(skb)->free == NAPI_GRO_FREE_STOLEN_HEAD)
		napi_skb_free_stolen_head(skb);
		else
		__kfree_skb(skb);
		}
		break;

		case GRO_HELD:
		@@ -4858,7 +4862,13 @@ static gro_result_t napi_frags_finish(struct napi_struct *napi,
		break;

		case GRO_DROP:
		napi_reuse_skb(napi, skb);
		break;

		case GRO_MERGED_FREE:
		if (NAPI_GRO_CB(skb)->free == NAPI_GRO_FREE_STOLEN_HEAD)
		napi_skb_free_stolen_head(skb);
		else
		napi_reuse_skb(napi, skb);
		break;

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