netdev - Re: [tipc-discussion] [net v2 1/1] tipc: fix memory leak caused by tipc_buf

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Message-ID: <20201026115456.4a620262@kicinski-fedora-PC1C0HJN.hsd1.ca.comcast.net>
Date:   Mon, 26 Oct 2020 11:54:59 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Tung Nguyen <tung.q.nguyen@...tech.com.au>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        tipc-discussion@...ts.sourceforge.net
Subject: Re: [tipc-discussion] [net v2 1/1] tipc: fix memory leak caused by
 tipc_buf_append()

On Mon, 26 Oct 2020 17:43:33 +0700 Tung Nguyen wrote:
> Commit ed42989eab57 ("fix the skb_unshare() in tipc_buf_append()")
> replaced skb_unshare() with skb_copy() to not reduce the data reference
> counter of the original skb intentionally. This is not the correct
> way to handle the cloned skb because it causes memory leak in 2
> following cases:
>  1/ Sending multicast messages via broadcast link
>   The original skb list is cloned to the local skb list for local
>   destination. After that, the data reference counter of each skb
>   in the original list has the value of 2. This causes each skb not
>   to be freed after receiving ACK:
>   tipc_link_advance_transmq()
>   {
>    ...
>    /* release skb */
>    __skb_unlink(skb, &l->transmq);
>    kfree_skb(skb); <-- memory exists after being freed
>   }
> 
>  2/ Sending multicast messages via replicast link
>   Similar to the above case, each skb cannot be freed after purging
>   the skb list:
>   tipc_mcast_xmit()
>   {
>    ...
>    __skb_queue_purge(pkts); <-- memory exists after being freed
>   }
> 
> This commit fixes this issue by using skb_unshare() instead. Besides,
> to avoid use-after-free error reported by KASAN, the pointer to the
> fragment is set to NULL before calling skb_unshare() to make sure that
> the original skb is not freed after freeing the fragment 2 times in
> case skb_unshare() returns NULL.
> 
> Fixes: ed42989eab57 ("fix the skb_unshare() in tipc_buf_append()")
> Acked-by: Jon Maloy <jmaloy@...hat.com>
> Reported-by: Thang Hoang Ngo <thang.h.ngo@...tech.com.au>
> Signed-off-by: Tung Nguyen <tung.q.nguyen@...tech.com.au>

Fixes tag: Fixes: ed42989eab57 ("fix the skb_unshare() in tipc_buf_append()")
Has these problem(s):
	- Subject does not match target commit subject
	  Just use
		git log -1 --format='Fixes: %h ("%s")'