Re: [bpf PATCH 3/3] bpf: sockmap, fix error handling in redirect failures

[David Miller <davem@davemloft.net>]

From: John Fastabend <john.fastabend@gmail.com>
Date: Wed, 02 May 2018 10:47:37 -0700

> When a redirect failure happens we release the buffers in-flight
> without calling a sk_mem_uncharge(), the uncharge is called before
> dropping the sock lock for the redirecte, however we missed updating
> the ring start index. When no apply actions are in progress this
> is OK because we uncharge the entire buffer before the redirect.
> But, when we have apply logic running its possible that only a
> portion of the buffer is being redirected. In this case we only
> do memory accounting for the buffer slice being redirected and
> expect to be able to loop over the BPF program again and/or if
> a sock is closed uncharge the memory at sock destruct time.
> 
> With an invalid start index however the program logic looks at
> the start pointer index, checks the length, and when seeing the
> length is zero (from the initial release and failure to update
> the pointer) aborts without uncharging/releasing the remaining
> memory.
> 
> The fix for this is simply to update the start index. To avoid
> fixing this error in two locations we do a small refactor and
> remove one case where it is open-coded. Then fix it in the
> single function.
> 
> Signed-off-by: John Fastabend <john.fastabend@gmail.com>

Acked-by: David S. Miller <davem@davemloft.net>