netdev - Re: [bpf PATCH 1/2] bpf: sockmap update rollback on error can incorrectly dec prog refcnt

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Message-ID: <20180517161555.aihomufufxyj273z@kafai-mbp.dhcp.thefacebook.com>
Date:   Thu, 17 May 2018 09:15:57 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     John Fastabend <john.fastabend@...il.com>
CC:     <ast@...nel.org>, <daniel@...earbox.net>, <netdev@...r.kernel.org>
Subject: Re: [bpf PATCH 1/2] bpf: sockmap update rollback on error can
 incorrectly dec prog refcnt

On Wed, May 16, 2018 at 02:46:51PM -0700, John Fastabend wrote:
> If the user were to only attach one of the parse or verdict programs
> then it is possible a subsequent sockmap update could incorrectly
> decrement the refcnt on the program. This happens because in the
> rollback logic, after an error, we have to decrement the program
> reference count when its been incremented. However, we only increment
> the program reference count if the user has both a verdict and a
> parse program. The reason for this is because, at least at the
> moment, both are required for any one to be meaningful. The problem
> fixed here is in the rollback path we decrement the program refcnt
> even if only one existing. But we never incremented the refcnt in
> the first place creating an imbalance.
> 
> This patch fixes the error path to handle this case.
> 
> Fixes: 2f857d04601a ("bpf: sockmap, remove STRPARSER map_flags and add multi-map support")
> Reported-by: Daniel Borkmann <daniel@...earbox.net>
> Signed-off-by: John Fastabend <john.fastabend@...il.com>
Acked-by: Martin KaFai Lau <kafai@...com>