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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Alexander Lobakin <alobakin@pm.me>,
        Antoine Tenart <atenart@kernel.org>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 5.13 130/156] net: do not reuse skbuff allocated from skbuff_fclone_cache in the skb cache
Date:   Thu, 22 Jul 2021 18:31:45 +0200
Message-Id: <20210722155632.562876548@linuxfoundation.org>
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From: Antoine Tenart <atenart@kernel.org>

commit 28b34f01a73435a754956ebae826e728c03ffa38 upstream.

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

napi_skb_finish
  __kfree_skb_defer
    napi_skb_cache_put

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 <alobakin@pm.me>
Signed-off-by: Antoine Tenart <atenart@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/core/dev.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6194,6 +6194,8 @@ static gro_result_t napi_skb_finish(stru
 	case GRO_MERGED_FREE:
 		if (NAPI_GRO_CB(skb)->free == NAPI_GRO_FREE_STOLEN_HEAD)
 			napi_skb_free_stolen_head(skb);
+		else if (skb->fclone != SKB_FCLONE_UNAVAILABLE)
+			__kfree_skb(skb);
 		else
 			__kfree_skb_defer(skb);
 		break;