linux-kernel - Re: [syzbot] KASAN: use-after-free Read in rxrpc_lookup

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <1359657.1670414268@warthog.procyon.org.uk>
Date:   Wed, 07 Dec 2022 11:57:48 +0000
From:   David Howells <dhowells@...hat.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     dhowells@...hat.com,
        syzbot <syzbot+3538a6a72efa8b059c38@...kaller.appspotmail.com>,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] KASAN: use-after-free Read in rxrpc_lookup_local

Hillf Danton <hdanton@...a.com> wrote:

> To fix the uaf, destroy local in workqueue because of hlist_del under mutex.

Hmmm...  That can't be the whole explanation.  As you say, the hlist_del is
done under the mutex in rxrpc_destroy_local() - the same as the
hlist_add/hlist_replace and the search in rxrpc_lookup_local().

There should be no need to bump it off to a worker thread - the destruction is
in process context already - and doing the destruction not in the I/O thread
violates other assumptions, so I'm not convinced this patch is a valid fix.

I wonder if, under some circumstances, the I/O thread is managing to start and
destroy itself *before* rxrpc_lookup_local() adds itself to the
local_endpoints list.  Possibly I should offload the add to the I/O thread and
use a completion to wait for it to set up.

David