This is a note to let you know that I've just added the patch titled net: do not reuse skbuff allocated from skbuff_fclone_cache in the skb cache to the 5.13-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: net-do-not-reuse-skbuff-allocated-from-skbuff_fclone_cache-in-the-skb-cache.patch and it can be found in the queue-5.13 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 28b34f01a73435a754956ebae826e728c03ffa38 Mon Sep 17 00:00:00 2001 From: Antoine Tenart <atenart@xxxxxxxxxx> Date: Fri, 9 Jul 2021 18:16:09 +0200 Subject: net: do not reuse skbuff allocated from skbuff_fclone_cache in the skb cache From: Antoine Tenart <atenart@xxxxxxxxxx> 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@xxxxx> Signed-off-by: Antoine Tenart <atenart@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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; Patches currently in stable-queue which might be from atenart@xxxxxxxxxx are queue-5.13/net-do-not-reuse-skbuff-allocated-from-skbuff_fclone_cache-in-the-skb-cache.patch