[
https://issues.apache.org/jira/browse/GUACAMOLE-428?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Aiden Luo updated GUACAMOLE-428:
--------------------------------
Description:
1. core dump
{code:c}
Program terminated with signal SIGSEGV, Segmentation fault.
#0 0x00007f932c1763dc in guac_vnc_user_leave_handler (user=0x7f9328004980) at
user.c:116
116 guac_common_cursor_remove_user(vnc_client->display->cursor, user);
(gdb) bt
#0 0x00007f932c1763dc in guac_vnc_user_leave_handler (user=0x7f9328004980) at
user.c:116
#1 0x00007f93322d1f7f in guac_client_remove_user (client=0x7f92b800ad90,
user=0x7f9328004980) at client.c:339
#2 0x0000000000405c60 in guacd_handle_user (user=0x7f9328004980) at user.c:304
#3 0x0000000000404ca2 in guacd_user_thread (data=0x7f92b801bac0) at proc.c:95
#4 0x00007f9331922064 in start_thread (arg=0x7f92b37fe700) at
pthread_create.c:309
#5 0x00007f9330b0562d in clone () at
../sysdeps/unix/sysv/linux/x86_64/clone.S:111
(gdb) l
111 int guac_vnc_user_leave_handler(guac_user* user) {
112
113 guac_vnc_client* vnc_client = (guac_vnc_client*) user->client->data;
114
115 /* Update shared cursor state */
116 guac_common_cursor_remove_user(vnc_client->display->cursor, user);
117
118 /* Free settings if not owner (owner settings will be freed with
client) */
119 if (!user->owner) {
120 guac_vnc_settings* settings = (guac_vnc_settings*) user->data;
(gdb) p *vnc_client
$1 = {client_thread = 140268061849344, rfb_client = 0x0, rfb_MallocFrameBuffer
= 0x7f931f5f5030, copy_rect_used = 0,
settings = 0x7f9328006890, display = 0x0, clipboard = 0x7f92b8035b60, audio =
0x0, sftp_user = 0x0, sftp_session = 0x0,
sftp_filesystem = 0x0, clipboard_reader = 0x7f932c1782de
<GUAC_READ_ISO8859_1>,
clipboard_writer = 0x7f932c178414 <GUAC_WRITE_ISO8859_1>}
(gdb) p *user
$2 = {client = 0x7f92b800ad90, socket = 0x7f932800af30, user_id =
0x7f9328004c30 "@b4e03b65-8317-4049-9f73-61c9a92272f9",
owner = 1, active = 0, __prev = 0x0, __next = 0x0, last_received_timestamp =
1586735641, last_frame_duration = 0,
processing_lag = 0, info = {optimal_width = 977, optimal_height = 668,
audio_mimetypes = 0x7f932800b000,
video_mimetypes = 0x7f932800b020, image_mimetypes = 0x7f9328004ae0,
optimal_resolution = 96},
__stream_pool = 0x7f9328004a90, __output_streams = 0x7f9328005670,
__input_streams = 0x7f9328004c60,
__object_pool = 0x7f932800afb0, __objects = 0x7f9328006080, data =
0x7f9328006890,
mouse_handler = 0x7f932c17592e <guac_vnc_user_mouse_handler>, key_handler =
0x7f932c1759a7 <guac_vnc_user_key_handler>,
clipboard_handler = 0x7f932c174ea1 <guac_vnc_clipboard_handler>, size_handler
= 0x0, file_handler = 0x0,
pipe_handler = 0x0, ack_handler = 0x0, blob_handler = 0x0, end_handler = 0x0,
sync_handler = 0x0, leave_handler = 0x0,
get_handler = 0x0, put_handler = 0x0, audio_handler = 0x0}
{code}
2. analysis
When user connect to guacd, guacd will create a new process to handle the
connection. In new process then create `static void* guacd_user_thread(void*
data)` thread to do real work.
In guacd_user_thread thread, will create a +void*
guac_vnc_client_thread(void* data)+ thread to read frame from VNC server and
write to guac_socket. +vnc_client->clipboard_reader+,
+vnc_client->rfb_client+ and +vnc_client->display+ will be setup in this thread.
Also guacd_user_thread will create another +void* guacd_user_input_thread(void*
data)+ thread to receive data from client and send to VNC sever.
guacd_user_thread will wait guacd_user_input_thread finished, then call +void
guac_client_remove_user(guac_client* client, guac_user* user)+ function to
remove user which will call +int guac_vnc_user_leave_handler(guac_user*
user)+.
The segfault error caused by line
+guac_common_cursor_remove_user(vnc_client->display->cursor, user)+ in
function +guac_vnc_user_leave_handler+，because +vnc_client->display+ is NLL.
Why this segfault will happen?
My guess is that there exist concurrently problem. If guacd_user_input_thread
exit before +vnc_client->display+ gets initialized in guac_vnc_client_thread,
the +guac_common_cursor_remove_user+ function will do null pointer dereference.
We should check +vnc_client->display+ if is null in function +void
guac_client_remove_user(guac_client* client, guac_user* user)+.
was:
1. core dump
{code:c}
Program terminated with signal SIGSEGV, Segmentation fault.
#0 0x00007f932c1763dc in guac_vnc_user_leave_handler (user=0x7f9328004980) at
user.c:116
116 guac_common_cursor_remove_user(vnc_client->display->cursor, user);
(gdb) bt
#0 0x00007f932c1763dc in guac_vnc_user_leave_handler (user=0x7f9328004980) at
user.c:116
#1 0x00007f93322d1f7f in guac_client_remove_user (client=0x7f92b800ad90,
user=0x7f9328004980) at client.c:339
#2 0x0000000000405c60 in guacd_handle_user (user=0x7f9328004980) at user.c:304
#3 0x0000000000404ca2 in guacd_user_thread (data=0x7f92b801bac0) at proc.c:95
#4 0x00007f9331922064 in start_thread (arg=0x7f92b37fe700) at
pthread_create.c:309
#5 0x00007f9330b0562d in clone () at
../sysdeps/unix/sysv/linux/x86_64/clone.S:111
(gdb) l
111 int guac_vnc_user_leave_handler(guac_user* user) {
112
113 guac_vnc_client* vnc_client = (guac_vnc_client*) user->client->data;
114
115 /* Update shared cursor state */
116 guac_common_cursor_remove_user(vnc_client->display->cursor, user);
117
118 /* Free settings if not owner (owner settings will be freed with
client) */
119 if (!user->owner) {
120 guac_vnc_settings* settings = (guac_vnc_settings*) user->data;
(gdb) p *vnc_client
$1 = {client_thread = 140268061849344, rfb_client = 0x0, rfb_MallocFrameBuffer
= 0x7f931f5f5030, copy_rect_used = 0,
settings = 0x7f9328006890, display = 0x0, clipboard = 0x7f92b8035b60, audio =
0x0, sftp_user = 0x0, sftp_session = 0x0,
sftp_filesystem = 0x0, clipboard_reader = 0x7f932c1782de
<GUAC_READ_ISO8859_1>,
clipboard_writer = 0x7f932c178414 <GUAC_WRITE_ISO8859_1>}
(gdb) p *user
$2 = {client = 0x7f92b800ad90, socket = 0x7f932800af30, user_id =
0x7f9328004c30 "@b4e03b65-8317-4049-9f73-61c9a92272f9",
owner = 1, active = 0, __prev = 0x0, __next = 0x0, last_received_timestamp =
1586735641, last_frame_duration = 0,
processing_lag = 0, info = {optimal_width = 977, optimal_height = 668,
audio_mimetypes = 0x7f932800b000,
video_mimetypes = 0x7f932800b020, image_mimetypes = 0x7f9328004ae0,
optimal_resolution = 96},
__stream_pool = 0x7f9328004a90, __output_streams = 0x7f9328005670,
__input_streams = 0x7f9328004c60,
__object_pool = 0x7f932800afb0, __objects = 0x7f9328006080, data =
0x7f9328006890,
mouse_handler = 0x7f932c17592e <guac_vnc_user_mouse_handler>, key_handler =
0x7f932c1759a7 <guac_vnc_user_key_handler>,
clipboard_handler = 0x7f932c174ea1 <guac_vnc_clipboard_handler>, size_handler
= 0x0, file_handler = 0x0,
pipe_handler = 0x0, ack_handler = 0x0, blob_handler = 0x0, end_handler = 0x0,
sync_handler = 0x0, leave_handler = 0x0,
get_handler = 0x0, put_handler = 0x0, audio_handler = 0x0}
{code}
2. analysis
When user connect to guacd, guacd will create a new process to handle the
connection. In new process then create `static void* guacd_user_thread(void*
data)` thread to do real work.
In guacd_user_thread thread, will create a *void*
guac_vnc_client_thread(void* data)* thread to read frame from VNC server and
write to guac_socket. *vnc_client->clipboard_reader*,
*vnc_client->rfb_client* and *vnc_client->display* will be setup in this thread.
Also guacd_user_thread will create another *void* guacd_user_input_thread(void*
data)* thread to receive data from client and send to VNC sever.
guacd_user_thread will wait guacd_user_input_thread finished, then call *void
guac_client_remove_user(guac_client* client, guac_user* user)* function to
remove user which will call *int guac_vnc_user_leave_handler(guac_user*
user)*.
The segfault error caused by line
*guac_common_cursor_remove_user(vnc_client->display->cursor, user)* in
function *guac_vnc_user_leave_handler*，because *vnc_client->display* is NLL.
Why this segfault will happen?
My guess is that there exist concurrently problem. If guacd_user_input_thread
exit before *vnc_client->display* gets initialized in guac_vnc_client_thread,
the *guac_common_cursor_remove_user* function will do null pointer dereference.
We should check *vnc_client->display* if is null in function *void
guac_client_remove_user(guac_client* client, guac_user* user)*.
> segfault in guac_vnc_user_leave_handler
> ---------------------------------------
>
> Key: GUACAMOLE-428
> URL: https://issues.apache.org/jira/browse/GUACAMOLE-428
> Project: Guacamole
> Issue Type: Bug
> Components: VNC
> Affects Versions: 0.9.13-incubating
> Environment: guacd with container
> Reporter: Aiden Luo
> Priority: Major
>
> 1. core dump
> {code:c}
> Program terminated with signal SIGSEGV, Segmentation fault.
> #0 0x00007f932c1763dc in guac_vnc_user_leave_handler (user=0x7f9328004980)
> at user.c:116
> 116 guac_common_cursor_remove_user(vnc_client->display->cursor, user);
> (gdb) bt
> #0 0x00007f932c1763dc in guac_vnc_user_leave_handler (user=0x7f9328004980)
> at user.c:116
> #1 0x00007f93322d1f7f in guac_client_remove_user (client=0x7f92b800ad90,
> user=0x7f9328004980) at client.c:339
> #2 0x0000000000405c60 in guacd_handle_user (user=0x7f9328004980) at
> user.c:304
> #3 0x0000000000404ca2 in guacd_user_thread (data=0x7f92b801bac0) at proc.c:95
> #4 0x00007f9331922064 in start_thread (arg=0x7f92b37fe700) at
> pthread_create.c:309
> #5 0x00007f9330b0562d in clone () at
> ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
> (gdb) l
> 111 int guac_vnc_user_leave_handler(guac_user* user) {
> 112
> 113 guac_vnc_client* vnc_client = (guac_vnc_client*)
> user->client->data;
> 114
> 115 /* Update shared cursor state */
> 116 guac_common_cursor_remove_user(vnc_client->display->cursor, user);
> 117
> 118 /* Free settings if not owner (owner settings will be freed with
> client) */
> 119 if (!user->owner) {
> 120 guac_vnc_settings* settings = (guac_vnc_settings*) user->data;
> (gdb) p *vnc_client
> $1 = {client_thread = 140268061849344, rfb_client = 0x0,
> rfb_MallocFrameBuffer = 0x7f931f5f5030, copy_rect_used = 0,
> settings = 0x7f9328006890, display = 0x0, clipboard = 0x7f92b8035b60, audio
> = 0x0, sftp_user = 0x0, sftp_session = 0x0,
> sftp_filesystem = 0x0, clipboard_reader = 0x7f932c1782de
> <GUAC_READ_ISO8859_1>,
> clipboard_writer = 0x7f932c178414 <GUAC_WRITE_ISO8859_1>}
> (gdb) p *user
> $2 = {client = 0x7f92b800ad90, socket = 0x7f932800af30, user_id =
> 0x7f9328004c30 "@b4e03b65-8317-4049-9f73-61c9a92272f9",
> owner = 1, active = 0, __prev = 0x0, __next = 0x0, last_received_timestamp
> = 1586735641, last_frame_duration = 0,
> processing_lag = 0, info = {optimal_width = 977, optimal_height = 668,
> audio_mimetypes = 0x7f932800b000,
> video_mimetypes = 0x7f932800b020, image_mimetypes = 0x7f9328004ae0,
> optimal_resolution = 96},
> __stream_pool = 0x7f9328004a90, __output_streams = 0x7f9328005670,
> __input_streams = 0x7f9328004c60,
> __object_pool = 0x7f932800afb0, __objects = 0x7f9328006080, data =
> 0x7f9328006890,
> mouse_handler = 0x7f932c17592e <guac_vnc_user_mouse_handler>, key_handler =
> 0x7f932c1759a7 <guac_vnc_user_key_handler>,
> clipboard_handler = 0x7f932c174ea1 <guac_vnc_clipboard_handler>,
> size_handler = 0x0, file_handler = 0x0,
> pipe_handler = 0x0, ack_handler = 0x0, blob_handler = 0x0, end_handler =
> 0x0, sync_handler = 0x0, leave_handler = 0x0,
> get_handler = 0x0, put_handler = 0x0, audio_handler = 0x0}
> {code}
> 2. analysis
> When user connect to guacd, guacd will create a new process to handle the
> connection. In new process then create `static void* guacd_user_thread(void*
> data)` thread to do real work.
> In guacd_user_thread thread, will create a +void*
> guac_vnc_client_thread(void* data)+ thread to read frame from VNC server and
> write to guac_socket. +vnc_client->clipboard_reader+,
> +vnc_client->rfb_client+ and +vnc_client->display+ will be setup in this
> thread.
> Also guacd_user_thread will create another +void*
> guacd_user_input_thread(void* data)+ thread to receive data from client and
> send to VNC sever.
> guacd_user_thread will wait guacd_user_input_thread finished, then call +void
> guac_client_remove_user(guac_client* client, guac_user* user)+ function to
> remove user which will call +int guac_vnc_user_leave_handler(guac_user*
> user)+.
> The segfault error caused by line
> +guac_common_cursor_remove_user(vnc_client->display->cursor, user)+ in
> function +guac_vnc_user_leave_handler+，because +vnc_client->display+ is NLL.
> Why this segfault will happen?
> My guess is that there exist concurrently problem. If
> guacd_user_input_thread exit before +vnc_client->display+ gets initialized in
> guac_vnc_client_thread, the +guac_common_cursor_remove_user+ function will do
> null pointer dereference.
> We should check +vnc_client->display+ if is null in function +void
> guac_client_remove_user(guac_client* client, guac_user* user)+.
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