On 01/31/2018 07:44 PM, Daniel P. Berrangé wrote:
On Wed, Jan 31, 2018 at 07:25:21PM +0300, Klim Kireev wrote:
On one of our client's node, due to trying to read from closed ioc,
a segmentation fault occured. Corresponding backtrace:
0 object_get_class (obj=obj@entry=0x0)
1 qio_channel_readv_full (ioc=0x0, iov=0x7ffe55277180 ...
2 qio_channel_read (ioc=<optimized out> ...
3 vnc_client_read_buf (vs=vs@entry=0x55625f3c6000, ...
4 vnc_client_read_plain (vs=0x55625f3c6000)
5 vnc_client_read (vs=0x55625f3c6000)
6 vnc_client_io (ioc=<optimized out>, condition=G_IO_IN, ...
7 g_main_dispatch (context=0x556251568a50)
8 g_main_context_dispatch (context=context@entry=0x556251568a50)
9 glib_pollfds_poll ()
10 os_host_main_loop_wait (timeout=<optimized out>)
11 main_loop_wait (nonblocking=nonblocking@entry=0)
12 main_loop () at vl.c:1909
13 main (argc=<optimized out>, argv=<optimized out>, ...
Having analyzed the coredump, I understood that the reason is that
ioc_tag is reset on vnc_disconnect_start and ioc is cleaned
in vnc_disconnect_finish. Between these two events due to some
reasons the ioc_tag was set again and after vnc_disconnect_finish
the handler is running with freed ioc,
which led to the segmentation fault.
The patch checks vs->disconnecting in places where we call
qio_channel_add_watch to prevent such an occurrence.
Signed-off-by: Klim Kireev <klim.kir...@virtuozzo.com>
---
Changelog:
v2: Attach the backtrace
v3: Change checks
ui/vnc.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)
diff --git a/ui/vnc.c b/ui/vnc.c
index 33b087221f..708204fa7e 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -1407,13 +1407,19 @@ static void vnc_client_write_locked(VncState *vs)
} else
#endif /* CONFIG_VNC_SASL */
{
- vnc_client_write_plain(vs);
+ if (vs->disconnecting == FALSE) {
+ vnc_client_write_plain(vs);
+ } else {
+ if (vs->ioc_tag != 0) {
+ g_source_remove(vs->ioc_tag);
+ vs->ioc_tag = 0;
+ }
+ }
}
}
I'm not sure it is safe to only do the check in the else{} branch
of this code. If this code is reachable, then I think the SASL
branch will cause the same crash problems too. I think probably
need to push the checks up a level or two in the caller stack...
static void vnc_client_write(VncState *vs)
{
-
vnc_lock_output(vs);
if (vs->output.offset) {
vnc_client_write_locked(vs);
@@ -1421,8 +1427,12 @@ static void vnc_client_write(VncState *vs)
if (vs->ioc_tag) {
g_source_remove(vs->ioc_tag);
}
- vs->ioc_tag = qio_channel_add_watch(
- vs->ioc, G_IO_IN, vnc_client_io, vs, NULL);
+ if (vs->disconnecting == FALSE) {
+ vs->ioc_tag = qio_channel_add_watch(
+ vs->ioc, G_IO_IN, vnc_client_io, vs, NULL);
+ } else {
+ vs->ioc_tag = 0;
+ }
}
vnc_unlock_output(vs);
}
...I think perhaps we should do the check in the vnc_client_io()
method, and also in the vnc_flush() method.
I think we also need to put a check in the vnc_jobs_consume_buffer()
method, which can be triggered from a bottom-half.
Thank you for your advice,
in both places there is a check vs->ioc != NULL, so we don't need check
it there
Regards,
Daniel
