linux-kernel - Re: [PATCH net] rxrpc: Fix use-after-free in rxrpc_receive

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Date:   Mon, 27 Jan 2020 10:57:17 +0100 (CET)
From:   David Miller <davem@...emloft.net>
To:     dhowells@...hat.com
Cc:     netdev@...r.kernel.org, linux-afs@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] rxrpc: Fix use-after-free in rxrpc_receive_data()

From: David Howells <dhowells@...hat.com>
Date: Fri, 24 Jan 2020 23:08:04 +0000

> The subpacket scanning loop in rxrpc_receive_data() references the
> subpacket count in the private data part of the sk_buff in the loop
> termination condition.  However, when the final subpacket is pasted into
> the ring buffer, the function is no longer has a ref on the sk_buff and
> should not be looking at sp->* any more.  This point is actually marked in
> the code when skb is cleared (but sp is not - which is an error).
> 
> Fix this by caching sp->nr_subpackets in a local variable and using that
> instead.
> 
> Also clear 'sp' to catch accesses after that point.
> 
> This can show up as an oops in rxrpc_get_skb() if sp->nr_subpackets gets
> trashed by the sk_buff getting freed and reused in the meantime.
> 
> Fixes: e2de6c404898 ("rxrpc: Use info in skbuff instead of reparsing a jumbo packet")
> Signed-off-by: David Howells <dhowells@...hat.com>

Applied and queued up for -stable, thanks.