From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vegard Nossum Date: Sat, 23 Jul 2016 14:00:39 +0000 Subject: Re: [PATCH] net/sctp: always initialise sctp_ht_iter::start_fail Message-Id: <57937887.6030204@oracle.com> List-Id: References: <1469267543-24650-1-git-send-email-vegard.nossum@oracle.com> <20160723133929.GG9950@localhost.localdomain> In-Reply-To: <20160723133929.GG9950@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Marcelo Ricardo Leitner Cc: Vlad Yasevich , Neil Horman , linux-sctp@vger.kernel.org, "David S. Miller" , netdev@vger.kernel.org, Xin Long , Herbert Xu , "Eric W. Biederman" , stable@vger.kernel.org On 07/23/2016 03:39 PM, Marcelo Ricardo Leitner wrote: > On Sat, Jul 23, 2016 at 11:52:23AM +0200, Vegard Nossum wrote: >> seq_read() can call ->start() twice on the same iterator more than once >> (e.g. once through traverse() and once in seq_read() itself). > > But when traverse() returns the error, it goes to Done label, skipping > the call to ->start() from seq_read(), or am I missing something? I think you're right. > Though yes, if sctp_ht_iter memory is actually re-used without > initializting between seq_read()s, it triggers the issue you described. The sctp_ht_iter is allocated in sctp_assocs_seq_open()/sctp_remaddr_seq_open(), so I assume it's allocated on open(). > How did you trigger this, reading after an error on the file descriptor? I was using trinity, so I'm not quite sure a priori, but the problem was 100% reproducible before I applied the patch and seeing that it gets allocated on open() and is never cleared anywhere else, your suggestion sounds like the most plausible explanation :-) How about rewording the first paragraph as: """ sctp_transport_seq_start() does not currently clear iter->start_fail on success, but relies on it being zero when it is allocated (by seq_open_net()). This can be a problem in the following sequence: open() -- allocates iter (and implicitly sets iter->start_fail = 0) read() iter->start() -- fails and sets iter->start_fail = 1 iter->stop() -- doesn't call sctp_transport_walk_stop() (correct) read() again iter->start() -- succeeds, but doesn't change iter->start_fail iter->stop() -- doesn't call sctp_transport_walk_stop() (wrong) """ Let me know how that sounds. Thanks for looking so closely at it! Vegard