[Qemu-devel] [PATCH] vnc: fix segfault in closed connection handling

[Qemu-devel] [PATCH] vnc: fix segfault in closed connection handling

[Klim Kireev]

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 and resets handler if disconnecting == TRUE
to prevent such an occurrence.

Signed-off-by: Klim Kireev <klim.kireev@virtuozzo.com>
---
Changelog:
v2: Attach the backtrace

v3: Change checks

 ui/vnc-jobs.c |  6 ++++--
 ui/vnc.c      | 15 ++++++++++++++-
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/ui/vnc-jobs.c b/ui/vnc-jobs.c
index e326679dd0..868dddef4b 100644
--- a/ui/vnc-jobs.c
+++ b/ui/vnc-jobs.c
@@ -148,8 +148,10 @@ void vnc_jobs_consume_buffer(VncState *vs)
             if (vs->ioc_tag) {
                 g_source_remove(vs->ioc_tag);
             }
-            vs->ioc_tag = qio_channel_add_watch(
-                vs->ioc, G_IO_IN | G_IO_OUT, vnc_client_io, vs, NULL);
+            if (vs->disconnecting == FALSE) {
+                vs->ioc_tag = qio_channel_add_watch(
+                    vs->ioc, G_IO_IN | G_IO_OUT, vnc_client_io, vs, NULL);
+            }
         }
         buffer_move(&vs->output, &vs->jobs_buffer);
 
diff --git a/ui/vnc.c b/ui/vnc.c
index 93731accb6..67ccc8160f 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -1536,12 +1536,19 @@ gboolean vnc_client_io(QIOChannel *ioc G_GNUC_UNUSED,
     VncState *vs = opaque;
     if (condition & G_IO_IN) {
         if (vnc_client_read(vs) < 0) {
-            return TRUE;
+            goto end;
         }
     }
     if (condition & G_IO_OUT) {
         vnc_client_write(vs);
     }
+end:
+    if (vs->disconnecting) {
+        if (vs->ioc_tag != 0) {
+            g_source_remove(vs->ioc_tag);
+        }
+        vs->ioc_tag = 0;
+    }
     return TRUE;
 }
 
@@ -1630,6 +1637,12 @@ void vnc_flush(VncState *vs)
     if (vs->ioc != NULL && vs->output.offset) {
         vnc_client_write_locked(vs);
     }
+    if (vs->disconnecting) {
+        if (vs->ioc_tag != 0) {
+            g_source_remove(vs->ioc_tag);
+        }
+        vs->ioc_tag = 0;
+    }
     vnc_unlock_output(vs);
 }
 
-- 
2.14.3

Re: [Qemu-devel] [PATCH v3] vnc: fix segfault in closed connection handling

[Klim Kireev]

ping

On 02/07/2018 12:48 PM, 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 and resets handler if disconnecting == TRUE
> to prevent such an occurrence.
>
> Signed-off-by: Klim Kireev <klim.kireev@virtuozzo.com>
> ---
> Changelog:
> v2: Attach the backtrace
>
> v3: Change checks
>
>   ui/vnc-jobs.c |  6 ++++--
>   ui/vnc.c      | 15 ++++++++++++++-
>   2 files changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/ui/vnc-jobs.c b/ui/vnc-jobs.c
> index e326679dd0..868dddef4b 100644
> --- a/ui/vnc-jobs.c
> +++ b/ui/vnc-jobs.c
> @@ -148,8 +148,10 @@ void vnc_jobs_consume_buffer(VncState *vs)
>               if (vs->ioc_tag) {
>                   g_source_remove(vs->ioc_tag);
>               }
> -            vs->ioc_tag = qio_channel_add_watch(
> -                vs->ioc, G_IO_IN | G_IO_OUT, vnc_client_io, vs, NULL);
> +            if (vs->disconnecting == FALSE) {
> +                vs->ioc_tag = qio_channel_add_watch(
> +                    vs->ioc, G_IO_IN | G_IO_OUT, vnc_client_io, vs, NULL);
> +            }
>           }
>           buffer_move(&vs->output, &vs->jobs_buffer);
>   
> diff --git a/ui/vnc.c b/ui/vnc.c
> index 93731accb6..67ccc8160f 100644
> --- a/ui/vnc.c
> +++ b/ui/vnc.c
> @@ -1536,12 +1536,19 @@ gboolean vnc_client_io(QIOChannel *ioc G_GNUC_UNUSED,
>       VncState *vs = opaque;
>       if (condition & G_IO_IN) {
>           if (vnc_client_read(vs) < 0) {
> -            return TRUE;
> +            goto end;
>           }
>       }
>       if (condition & G_IO_OUT) {
>           vnc_client_write(vs);
>       }
> +end:
> +    if (vs->disconnecting) {
> +        if (vs->ioc_tag != 0) {
> +            g_source_remove(vs->ioc_tag);
> +        }
> +        vs->ioc_tag = 0;
> +    }
>       return TRUE;
>   }
>   
> @@ -1630,6 +1637,12 @@ void vnc_flush(VncState *vs)
>       if (vs->ioc != NULL && vs->output.offset) {
>           vnc_client_write_locked(vs);
>       }
> +    if (vs->disconnecting) {
> +        if (vs->ioc_tag != 0) {
> +            g_source_remove(vs->ioc_tag);
> +        }
> +        vs->ioc_tag = 0;
> +    }
>       vnc_unlock_output(vs);
>   }
>   

Re: [Qemu-devel] [PATCH] vnc: fix segfault in closed connection handling

[Daniel P. Berrangé]

On Wed, Feb 07, 2018 at 12:48:44PM +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 and resets handler if disconnecting == TRUE
> to prevent such an occurrence.
> 
> Signed-off-by: Klim Kireev <klim.kireev@virtuozzo.com>
> ---
> Changelog:
> v2: Attach the backtrace
> 
> v3: Change checks
> 
>  ui/vnc-jobs.c |  6 ++++--
>  ui/vnc.c      | 15 ++++++++++++++-
>  2 files changed, 18 insertions(+), 3 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


> 
> diff --git a/ui/vnc-jobs.c b/ui/vnc-jobs.c
> index e326679dd0..868dddef4b 100644
> --- a/ui/vnc-jobs.c
> +++ b/ui/vnc-jobs.c
> @@ -148,8 +148,10 @@ void vnc_jobs_consume_buffer(VncState *vs)
>              if (vs->ioc_tag) {
>                  g_source_remove(vs->ioc_tag);
>              }
> -            vs->ioc_tag = qio_channel_add_watch(
> -                vs->ioc, G_IO_IN | G_IO_OUT, vnc_client_io, vs, NULL);
> +            if (vs->disconnecting == FALSE) {
> +                vs->ioc_tag = qio_channel_add_watch(
> +                    vs->ioc, G_IO_IN | G_IO_OUT, vnc_client_io, vs, NULL);
> +            }
>          }
>          buffer_move(&vs->output, &vs->jobs_buffer);
>  
> diff --git a/ui/vnc.c b/ui/vnc.c
> index 93731accb6..67ccc8160f 100644
> --- a/ui/vnc.c
> +++ b/ui/vnc.c
> @@ -1536,12 +1536,19 @@ gboolean vnc_client_io(QIOChannel *ioc G_GNUC_UNUSED,
>      VncState *vs = opaque;
>      if (condition & G_IO_IN) {
>          if (vnc_client_read(vs) < 0) {
> -            return TRUE;
> +            goto end;
>          }
>      }
>      if (condition & G_IO_OUT) {
>          vnc_client_write(vs);
>      }
> +end:
> +    if (vs->disconnecting) {
> +        if (vs->ioc_tag != 0) {
> +            g_source_remove(vs->ioc_tag);
> +        }
> +        vs->ioc_tag = 0;
> +    }
>      return TRUE;
>  }
>  
> @@ -1630,6 +1637,12 @@ void vnc_flush(VncState *vs)
>      if (vs->ioc != NULL && vs->output.offset) {
>          vnc_client_write_locked(vs);
>      }
> +    if (vs->disconnecting) {
> +        if (vs->ioc_tag != 0) {
> +            g_source_remove(vs->ioc_tag);
> +        }
> +        vs->ioc_tag = 0;
> +    }
>      vnc_unlock_output(vs);
>  }
>  
> -- 
> 2.14.3
> 

Regards,
Daniel
-- 
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|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
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Re: [Qemu-devel] [PATCH v3] vnc: fix segfault in closed connection handling

[Gerd Hoffmann]

On Wed, Feb 14, 2018 at 05:43:19PM +0300, Klim Kireev wrote:
> ping

Queued now.  Was lingering in my inbox, waiting for me to find the time
for the next ui pull request.

cheers,
  Gerd

Re: [Qemu-devel] [PATCH] vnc: fix segfault in closed connection handling

[klim]

On 01/31/2018 04:16 PM, Marc-André Lureau wrote:
> Hi
>
> On Wed, Jan 31, 2018 at 2:06 PM, Klim Kireev <klim.kireev@virtuozzo.com> wrote:
>> On one of our client's node, due to trying to read from closed ioc,
>> a segmentation fault occured. Corresponding backtrace:
>>
> Oops, you probably forgot an extra space before the # interpreted as comment.
Thanks, fixed
>
> Do you have a reproducer?
Unfortunately, no
>> 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>
>> ---
>>   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
>>
>>
>
>

Re: [Qemu-devel] [PATCH] vnc: fix segfault in closed connection handling

[Marc-André Lureau]

Hi

On Wed, Jan 31, 2018 at 2:06 PM, Klim Kireev <klim.kireev@virtuozzo.com> wrote:
> On one of our client's node, due to trying to read from closed ioc,
> a segmentation fault occured. Corresponding backtrace:
>

Oops, you probably forgot an extra space before the # interpreted as comment.

Do you have a reproducer?

> 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>
> ---
>  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
>
>



-- 
Marc-André Lureau

[Qemu-devel] [PATCH] vnc: fix segfault in closed connection handling

[Klim Kireev]

On one of our client's node, due to trying to read from closed ioc,
a segmentation fault occured. Corresponding backtrace:

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>
---
 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