From 78d01598aea85841f0e4f8baf62c42b76230a81c Mon Sep 17 00:00:00 2001 From: Alberto Garcia Date: Mon, 12 Aug 2019 18:58:29 +0300 Subject: [PATCH] char-socket: Lock tcp_chr_disconnect() and socket_reconnect_timeout() 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 This patch adds a lock to protect tcp_chr_disconnect() and socket_reconnect_timeout() Signed-off-by: Alberto Garcia Signed-off-by: Andrey Shinkevich Message-Id: <1565625509-404969-3-git-send-email-andrey.shinkevich@virtuozzo.com> Signed-off-by: Paolo Bonzini --- chardev/char-socket.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/chardev/char-socket.c b/chardev/char-socket.c index 7ca5d97af3..03f03407b0 100644 --- a/chardev/char-socket.c +++ b/chardev/char-socket.c @@ -150,7 +150,7 @@ static void tcp_chr_accept(QIONetListener *listener, void *opaque); static int tcp_chr_read_poll(void *opaque); -static void tcp_chr_disconnect(Chardev *chr); +static void tcp_chr_disconnect_locked(Chardev *chr); /* Called with chr_write_lock held. */ static int tcp_chr_write(Chardev *chr, const uint8_t *buf, int len) @@ -174,7 +174,7 @@ 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) { - tcp_chr_disconnect(chr); + tcp_chr_disconnect_locked(chr); return len; } /* else let the read handler finish it properly */ } @@ -469,8 +469,9 @@ static void update_disconnected_filename(SocketChardev *s) /* NB may be called even if tcp_chr_connect has not been * reached, due to TLS or telnet initialization failure, * so can *not* assume s->state == TCP_CHARDEV_STATE_CONNECTED + * This must be called with chr->chr_write_lock held. */ -static void tcp_chr_disconnect(Chardev *chr) +static void tcp_chr_disconnect_locked(Chardev *chr) { SocketChardev *s = SOCKET_CHARDEV(chr); bool emit_close = s->state == TCP_CHARDEV_STATE_CONNECTED; @@ -490,6 +491,13 @@ static void tcp_chr_disconnect(Chardev *chr) } } +static void tcp_chr_disconnect(Chardev *chr) +{ + qemu_mutex_lock(&chr->chr_write_lock); + tcp_chr_disconnect_locked(chr); + qemu_mutex_unlock(&chr->chr_write_lock); +} + static gboolean tcp_chr_read(QIOChannel *chan, GIOCondition cond, void *opaque) { Chardev *chr = CHARDEV(opaque); @@ -1131,8 +1139,10 @@ static gboolean socket_reconnect_timeout(gpointer opaque) Chardev *chr = CHARDEV(opaque); SocketChardev *s = SOCKET_CHARDEV(opaque); + qemu_mutex_lock(&chr->chr_write_lock); g_source_unref(s->reconnect_timer); s->reconnect_timer = NULL; + qemu_mutex_unlock(&chr->chr_write_lock); if (chr->be_open) { return false;