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Subject[PATCH 5.10 029/167] net: do not reuse skbuff allocated from skbuff_fclone_cache in the skb cache
From: Antoine Tenart <>

[ Upstream commit 28b34f01a73435a754956ebae826e728c03ffa38 ]

Some socket buffers allocated in the fclone cache (in __alloc_skb) can
end-up in the following path[1]:


The issue is napi_skb_cache_put is not fclone friendly and will put
those skbuff in the skb cache to be reused later, although this cache
only expects skbuff allocated from skbuff_head_cache. When this happens
the skbuff is eventually freed using the wrong origin cache, and we can
see traces similar to:

[ 1223.947534] cache_from_obj: Wrong slab cache. skbuff_head_cache but object is from skbuff_fclone_cache
[ 1223.948895] WARNING: CPU: 3 PID: 0 at mm/slab.h:442 kmem_cache_free+0x251/0x3e0
[ 1223.950211] Modules linked in:
[ 1223.950680] CPU: 3 PID: 0 Comm: swapper/3 Not tainted 5.13.0+ #474
[ 1223.951587] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-3.fc34 04/01/2014
[ 1223.953060] RIP: 0010:kmem_cache_free+0x251/0x3e0

Leading sometimes to other memory related issues.

Fix this by using __kfree_skb for fclone skbuff, similar to what is done
the other place __kfree_skb_defer is called.

[1] At least in setups using veth pairs and tunnels. Building a kernel
with KASAN we can for example see packets allocated in
sk_stream_alloc_skb hit the above path and later the issue arises
when the skbuff is reused.

Fixes: 9243adfc311a ("skbuff: queue NAPI_MERGED_FREE skbs into NAPI cache instead of freeing")
Cc: Alexander Lobakin <>
Signed-off-by: Antoine Tenart <>
Signed-off-by: David S. Miller <>
Signed-off-by: Sasha Levin <>
net/core/dev.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 6b08de52bf0e..86a0fe0f4c02 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6100,6 +6100,8 @@ static gro_result_t napi_skb_finish(struct napi_struct *napi,
+ else if (skb->fclone != SKB_FCLONE_UNAVAILABLE)
+ __kfree_skb(skb);

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