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bh=b26UN0r+T3wLi3xILlngnOJ6FYUScbcVZfM38xUEXg0=; b=TnGOqJtOmI5iK2LVF65pCrLLR8995FgKspUdLeYtd+Ek8ofrgIwNFh5xyLTPWnzWZkEA7D Llyldq6DH6jHQl1oEl4BXwp9oJ5/jvpgkhHaatougK8odHxLLVKFo9ESXj7hVxQiKDec97 UyXpUCeaIL0LtbPGKGilHS7EaH8tAcs= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-244-Di8snGT-N4KutdZryhAy4g-1; Tue, 13 Apr 2021 09:33:17 -0400 X-MC-Unique: Di8snGT-N4KutdZryhAy4g-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0332510E174C; Tue, 13 Apr 2021 13:32:42 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-114-55.ams2.redhat.com [10.36.114.55]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B32466267B; Tue, 13 Apr 2021 13:32:40 +0000 (UTC) Subject: Re: [PATCH for-6.0] block/nbd: fix possible use after free of s->connect_thread To: Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org References: <20210406155114.1057355-1-vsementsov@virtuozzo.com> From: Max Reitz Message-ID: <38417b0c-497f-1c41-d35e-8167bda0c2f7@redhat.com> Date: Tue, 13 Apr 2021 15:32:39 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mreitz@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=mreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, rvkagan@yandex-team.ru, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 13.04.21 14:19, Vladimir Sementsov-Ogievskiy wrote: > 13.04.2021 14:53, Max Reitz wrote: >> On 06.04.21 17:51, Vladimir Sementsov-Ogievskiy wrote: >>> If on nbd_close() we detach the thread (in >>> nbd_co_establish_connection_cancel() thr->state becomes >>> CONNECT_THREAD_RUNNING_DETACHED), after that point we should not use >>> s->connect_thread (which is set to NULL), as running thread may free it >>> at any time. >>> >>> Still nbd_co_establish_connection() does exactly this: it saves >>> s->connect_thread to local variable (just for better code style) and >>> use it even after yield point, when thread may be already detached. >>> >>> Fix that. Also check thr to be non-NULL on >>> nbd_co_establish_connection() start for safety. >>> >>> After this patch "case CONNECT_THREAD_RUNNING_DETACHED" becomes >>> impossible in the second switch in nbd_co_establish_connection(). >>> Still, don't add extra abort() just before the release. If it somehow >>> possible to reach this "case:" it won't hurt. Anyway, good refactoring >>> of all this reconnect mess will come soon. >>> >>> Signed-off-by: Vladimir Sementsov-Ogievskiy >>> --- >>> >>> Hi all! I faced a crash, just running 277 iotest in a loop. I can't >>> reproduce it on master, it reproduces only on my branch with nbd >>> reconnect refactorings. >>> >>> Still, it seems very possible that it may crash under some conditions. >>> So I propose this patch for 6.0. It's written so that it's obvious that >>> it will not hurt: >>> >>>   pre-patch, on first hunk we'll just crash if thr is NULL, >>>   on second hunk it's safe to return -1, and using thr when >>>   s->connect_thread is already zeroed is obviously wrong. >>> >>>   block/nbd.c | 11 +++++++++++ >>>   1 file changed, 11 insertions(+) >>> >>> diff --git a/block/nbd.c b/block/nbd.c >>> index c26dc5a54f..1d4668d42d 100644 >>> --- a/block/nbd.c >>> +++ b/block/nbd.c >>> @@ -443,6 +443,11 @@ nbd_co_establish_connection(BlockDriverState >>> *bs, Error **errp) >>>       BDRVNBDState *s = bs->opaque; >>>       NBDConnectThread *thr = s->connect_thread; >>> +    if (!thr) { >>> +        /* detached */ >>> +        return -1; >>> +    } >>> + >>>       qemu_mutex_lock(&thr->mutex); >>>       switch (thr->state) { >> >> First, it is a bit strange not to set *errp in these cases. > > Oops, right! ashamed) OK, so who cares. It wouldn’t do anything anyway. Apart from that, all the changes do is to turn use after frees or immediate NULL dereferences into clean errors. I can’t see any resources that should be cleaned up, so I hope Coverity won’t hate me for taking this patch. And then we’ll see whether Peter will take the pull request... Max