Re: [PATCH net] sctp: fix the check for _sctp_walk_params and _sctp_walk_errors

[David Miller <davem@davemloft.net>]

From: Xin Long <lucien.xin@gmail.com>
Date: Wed, 26 Jul 2017 16:24:59 +0800

> Commit b1f5bfc27a19 ("sctp: don't dereference ptr before leaving
> _sctp_walk_{params, errors}()") tried to fix the issue that it
> may overstep the chunk end for _sctp_walk_{params, errors} with
> 'chunk_end > offset(length) + sizeof(length)'.
> 
> But it introduced a side effect: When processing INIT, it verifies
> the chunks with 'param.v == chunk_end' after iterating all params
> by sctp_walk_params(). With the check 'chunk_end > offset(length)
> + sizeof(length)', it would return when the last param is not yet
> accessed. Because the last param usually is fwdtsn supported param
> whose size is 4 and 'chunk_end == offset(length) + sizeof(length)'
> 
> This is a badly issue even causing sctp couldn't process 4-shakes.
> Client would always get abort when connecting to server, due to
> the failure of INIT chunk verification on server.
> 
> The patch is to use 'chunk_end <= offset(length) + sizeof(length)'
> instead of 'chunk_end < offset(length) + sizeof(length)' for both
> _sctp_walk_params and _sctp_walk_errors.
> 
> Fixes: b1f5bfc27a19 ("sctp: don't dereference ptr before leaving _sctp_walk_{params, errors}()")
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Applied and queued up for -stable, thanks.