netdev - Re: [PATCH iproute2 master] bpf: Fix race condition with map pinning

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Date:   Fri, 20 Sep 2019 01:25:13 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Joe Stringer <joe@...d.net.nz>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        netdev@...r.kernel.org
Subject: Re: [PATCH iproute2 master] bpf: Fix race condition with map pinning

On Thu, Sep 19, 2019 at 03:07:33PM -0700, Joe Stringer wrote:
> If two processes attempt to invoke bpf_map_attach() at the same time,
> then they will both create maps, then the first will successfully pin
> the map to the filesystem and the second will not pin the map, but will
> continue operating with a reference to its own copy of the map. As a
> result, the sharing of the same map will be broken from the two programs
> that were concurrently loaded via loaders using this library.
> 
> Fix this by adding a retry in the case where the pinning fails because
> the map already exists on the filesystem. In that case, re-attempt
> opening a fd to the map on the filesystem as it shows that another
> program already created and pinned a map at that location.
> 
> Signed-off-by: Joe Stringer <joe@...d.net.nz>

Acked-by: Daniel Borkmann <daniel@...earbox.net>