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Lunev" Subject: [PULL v2 04/13] io/channel-socket: do not treat a zero length write as an error Date: Fri, 4 Sep 2026 17:06:34 +0100 Message-ID: <20260904160643.353833-5-berrange@redhat.com> In-Reply-To: <20260904160643.353833-1-berrange@redhat.com> References: <20260904160643.353833-1-berrange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 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, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org From: Denis V. Lunev qio_channel_socket_writev() checks "ret <= 0" after sendmsg(). A zero length iovec is written successfully and returns 0, so the success falls into the errno switch, which acts on whatever the last failing syscall left in errno. A stale EAGAIN turns it into QIO_CHANNEL_ERR_BLOCK with errp untouched, and a caller which treats every negative return as fatal then passes a NULL Error to error_get_pretty(). The websocket handshake does exactly that, so an unauthenticated client crashes QEMU during the greeting. Returning 0 is safe for callers which loop until everything is written. qio_channel_writev_full_all() has no zero progress guard, but iov_copy() yields no entries for a zero length write, so that loop is never entered. A connected stream socket returns 0 only when there is nothing to send. The WIN32 implementation in the same file uses "ret < 0". Fixes: CVE-2026-84788 Fixes: 559607ea173a ("io: add QIOChannelSocket class") Cc: qemu-stable@nongnu.org Cc: Daniel P. Berrangé Cc: Marc-André Lureau Reviewed-by: Daniel P. Berrangé Reviewed-by: Marc-André Lureau Signed-off-by: Denis V. Lunev Signed-off-by: Daniel P. Berrangé --- io/channel-socket.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/io/channel-socket.c b/io/channel-socket.c index 12773b832c..7920cee639 100644 --- a/io/channel-socket.c +++ b/io/channel-socket.c @@ -667,7 +667,7 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc, retry: ret = sendmsg(sioc->fd, &msg, sflags); - if (ret <= 0) { + if (ret < 0) { switch (errno) { case EAGAIN: return QIO_CHANNEL_ERR_BLOCK; -- 2.55.0