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.
I suggest to check ioc_tag in vnc_disconnect_finish to prevent such
an occurrence.
Signed-off-by: Klim Kireev <klim.kireev@virtuozzo.com>
---
Changelog:
v2: Apply the backtrace
ui/vnc.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/ui/vnc.c b/ui/vnc.c
index 33b087221f..b8bf0180cb 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -1270,6 +1270,10 @@ void vnc_disconnect_finish(VncState *vs)
}
g_free(vs->lossy_rect);
+ if (vs->ioc_tag) {
+ g_source_remove(vs->ioc_tag);
+ vs->ioc_tag = 0;
+ }
object_unref(OBJECT(vs->ioc));
vs->ioc = NULL;
object_unref(OBJECT(vs->sioc));
--
2.14.3
On Wed, Jan 31, 2018 at 04:15:37PM +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. > > I suggest to check ioc_tag in vnc_disconnect_finish to prevent such > an occurrence. I think the root cause here is some codepath failing to check the 'vs->disconnecting' flag. eg vnc_write() checks that before it calls qio_channel_add_watch. I suspect somewhere else in code needs such a check > > Signed-off-by: Klim Kireev <klim.kireev@virtuozzo.com> > --- > Changelog: > v2: Apply the backtrace > > ui/vnc.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/ui/vnc.c b/ui/vnc.c > index 33b087221f..b8bf0180cb 100644 > --- a/ui/vnc.c > +++ b/ui/vnc.c > @@ -1270,6 +1270,10 @@ void vnc_disconnect_finish(VncState *vs) > } > g_free(vs->lossy_rect); > > + if (vs->ioc_tag) { > + g_source_remove(vs->ioc_tag); > + vs->ioc_tag = 0; > + } > object_unref(OBJECT(vs->ioc)); > vs->ioc = NULL; > object_unref(OBJECT(vs->sioc)); Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
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