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Lunev" To: qemu-devel@nongnu.org Cc: den@openvz.org, qemu-stable@nongnu.org, =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= , =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= Subject: [PATCH 1/6] io/channel-socket: do not treat a zero length write as an error Date: Mon, 31 Aug 2026 12:01:46 +0200 Message-ID: <20260831100151.914178-2-den@openvz.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260831100151.914178-1-den@openvz.org> References: <20260831100151.914178-1-den@openvz.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::42b; envelope-from=den@openvz.org; helo=mail-wr1-x42b.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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: 559607ea173a ("io: add QIOChannelSocket class") Cc: qemu-stable@nongnu.org Cc: Daniel P. Berrangé Cc: Marc-André Lureau Signed-off-by: Denis V. Lunev --- 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; -- 2.53.0