From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:45538) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1grMZE-000172-8Y for qemu-devel@nongnu.org; Wed, 06 Feb 2019 07:44:41 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1grMZB-0006pc-FW for qemu-devel@nongnu.org; Wed, 06 Feb 2019 07:44:39 -0500 Received: from fanzine.igalia.com ([91.117.99.155]:58108) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1grMZ7-0006bS-L8 for qemu-devel@nongnu.org; Wed, 06 Feb 2019 07:44:35 -0500 From: Alberto Garcia Date: Wed, 6 Feb 2019 14:43:45 +0200 Message-Id: <20190206124345.14942-1-berto@igalia.com> Subject: [Qemu-devel] [RFC PATCH] char-socket: hold chr_write_lock during tcp_chr_free_connection() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Alberto Garcia , =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= , Paolo Bonzini There's a race condition in which the tcp_chr_read() ioc handler can close a connection that is being written to from another thread. Running iotest 136 in a loop triggers this problem and crashes QEMU. (gdb) bt #0 0x00005558b842902d in object_get_class (obj=0x0) at qom/object.c:860 #1 0x00005558b84f92db in qio_channel_writev_full (ioc=0x0, iov=0x7ffc355decf0, niov=1, fds=0x0, nfds=0, errp=0x0) at io/channel.c:76 #2 0x00005558b84e0e9e in io_channel_send_full (ioc=0x0, buf=0x5558baf5beb0, len=138, fds=0x0, nfds=0) at chardev/char-io.c:123 #3 0x00005558b84e4a69 in tcp_chr_write (chr=0x5558ba460380, buf=0x5558baf5beb0 "...", len=138) at chardev/char-socket.c:135 #4 0x00005558b84dca55 in qemu_chr_write_buffer (s=0x5558ba460380, buf=0x5558baf5beb0 "...", len=138, offset=0x7ffc355dedd0, write_all=false) at chardev/char.c:112 #5 0x00005558b84dcbc2 in qemu_chr_write (s=0x5558ba460380, buf=0x5558baf5beb0 "...", len=138, write_all=false) at chardev/char.c:147 #6 0x00005558b84dfb26 in qemu_chr_fe_write (be=0x5558ba476610, buf=0x5558baf5beb0 "...", len=138) at chardev/char-fe.c:42 #7 0x00005558b8088c86 in monitor_flush_locked (mon=0x5558ba476610) at monitor.c:406 #8 0x00005558b8088e8c in monitor_puts (mon=0x5558ba476610, str=0x5558ba921e49 "") at monitor.c:449 #9 0x00005558b8089178 in qmp_send_response (mon=0x5558ba476610, rsp=0x5558bb161600) at monitor.c:498 #10 0x00005558b808920c in monitor_qapi_event_emit (event=QAPI_EVENT_SHUTDOWN, qdict=0x5558bb161600) at monitor.c:526 #11 0x00005558b8089307 in monitor_qapi_event_queue_no_reenter (event=QAPI_EVENT_SHUTDOWN, qdict=0x5558bb161600) at monitor.c:551 #12 0x00005558b80896c0 in qapi_event_emit (event=QAPI_EVENT_SHUTDOWN, qdict=0x5558bb161600) at monitor.c:626 #13 0x00005558b855f23b in qapi_event_send_shutdown (guest=false, reason=SHUTDOWN_CAUSE_HOST_QMP_QUIT) at qapi/qapi-events-run-state.c:43 #14 0x00005558b81911ef in qemu_system_shutdown (cause=SHUTDOWN_CAUSE_HOST_QMP_QUIT) at vl.c:1837 #15 0x00005558b8191308 in main_loop_should_exit () at vl.c:1885 #16 0x00005558b819140d in main_loop () at vl.c:1924 #17 0x00005558b8198c84 in main (argc=18, argv=0x7ffc355df3f8, envp=0x7ffc355df490) at vl.c:4665 Signed-off-by: Alberto Garcia --- chardev/char-socket.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/chardev/char-socket.c b/chardev/char-socket.c index eaa8e8b68f..47bef1d2bd 100644 --- a/chardev/char-socket.c +++ b/chardev/char-socket.c @@ -148,7 +148,9 @@ static int tcp_chr_write(Chardev *chr, const uint8_t *buf, int len) if (ret < 0 && errno != EAGAIN) { if (tcp_chr_read_poll(chr) <= 0) { + qemu_mutex_unlock(&chr->chr_write_lock); tcp_chr_disconnect(chr); + qemu_mutex_lock(&chr->chr_write_lock); return len; } /* else let the read handler finish it properly */ } @@ -449,7 +451,9 @@ static void tcp_chr_disconnect(Chardev *chr) SocketChardev *s = SOCKET_CHARDEV(chr); bool emit_close = s->connected; + qemu_mutex_lock(&chr->chr_write_lock); tcp_chr_free_connection(chr); + qemu_mutex_unlock(&chr->chr_write_lock); if (s->listener) { qio_net_listener_set_client_func_full(s->listener, tcp_chr_accept, -- 2.11.0