From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Fastabend Subject: Re: [bpf-next PATCH] bpf: sockhash fix race with bpf_tcp_close and map delete Date: Mon, 28 May 2018 08:13:04 -0700 Message-ID: <35940fbd-c354-e5ad-8baf-678d8245389c@gmail.com> References: <20180525173712.4004.70590.stgit@john-Precision-Tower-5810> <9cae9278-fd9f-f90a-ca35-e2d4b3e63fe8@iogearbox.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: Daniel Borkmann , ast@kernel.org Return-path: Received: from mail-it0-f66.google.com ([209.85.214.66]:54960 "EHLO mail-it0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1033216AbeE1PNS (ORCPT ); Mon, 28 May 2018 11:13:18 -0400 Received: by mail-it0-f66.google.com with SMTP id z6-v6so15127199iti.4 for ; Mon, 28 May 2018 08:13:18 -0700 (PDT) In-Reply-To: <9cae9278-fd9f-f90a-ca35-e2d4b3e63fe8@iogearbox.net> Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 05/27/2018 03:36 PM, Daniel Borkmann wrote: > On 05/25/2018 07:37 PM, John Fastabend wrote: >> syzbot reported two related splats, a use after free and null >> pointer dereference, when a TCP socket is closed while the map is >> also being removed. >> >> The psock keeps a reference to all map slots that have a reference >> to the sock so that when the sock is closed we can clean up any >> outstanding sock{map|hash} entries. This avoids pinning a sock >> forever if the map owner fails to do proper cleanup. However, the >> result is we have two paths that can free an entry in the map. Even >> the comment in the sock{map|hash} tear down function, sock_hash_free() >> notes this: >> >> At this point no update, lookup or delete operations can happen. >> However, be aware we can still get a socket state event updates, >> and data ready callbacks that reference the psock from sk_user_data. >> >> Both removal paths omitted taking the hash bucket lock resulting >> in the case where we have two references that are in the process >> of being free'd. >> >> Reported-by: syzbot+a761b81c211794fa1072@syzkaller.appspotmail.com >> Signed-off-by: John Fastabend > > Applied to bpf-next, thanks John! > This needs a v2 it introduces a slightly different/related error. I'll have a v2 shortly.