2edadf26f1
If a client is in the process of being closed down, then its client->osPrivate
pointer will be set to NULL by CloseDownConnection. This can cause a crash if
freeing the client's resources results in a call to AttendClient. For example,
if the client has a pending sync fence:
Thread 1 "X" received signal SIGSEGV, Segmentation fault.
AttendClient (client=0x5571c4aed9a0) at ../os/connection.c:942
(gdb) bt
#0 AttendClient (client=0x5571c4aed9a0) at ../os/connection.c:942
#1 0x00005571c3dbb865 in SyncAwaitTriggerFired (pTrigger=<optimized out>) at ../Xext/sync.c:694
#2 0x00005571c3dd5749 in miSyncDestroyFence (pFence=0x5571c5063980) at ../miext/sync/misync.c:120
#3 0x00005571c3dbbc69 in FreeFence (obj=<optimized out>, id=<optimized out>) at ../Xext/sync.c:1909
#4 0x00005571c3d7a01d in doFreeResource (res=0x5571c506e3d0, skip=skip@entry=0) at ../dix/resource.c:880
#5 0x00005571c3d7b1dc in FreeClientResources (client=0x5571c4aed9a0) at ../dix/resource.c:1146
#6 FreeClientResources (client=0x5571c4aed9a0) at ../dix/resource.c:1109
#7 0x00005571c3d5525f in CloseDownClient (client=0x5571c4aed9a0) at ../dix/dispatch.c:3473
#8 0x00005571c3d55eeb in Dispatch () at ../dix/dispatch.c:492
#9 0x00005571c3d59e96 in dix_main (argc=3, argv=0x7ffe7854bc28, envp=<optimized out>) at ../dix/main.c:276
#10 0x00007fea4837cb6b in __libc_start_main (main=0x5571c3d1d060 <main>, argc=3, argv=0x7ffe7854bc28, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7ffe7854bc18) at ../csu/libc-start.c:308
#11 0x00005571c3d1d09a in _start () at ../Xext/sync.c:2378
(gdb) print client->osPrivate
$1 = (void *) 0x0
Since the client is about to be freed, its ignore count doesn't matter and
AttendClient can simply be a no-op. Check for client->clientGone in AttendClient
and remove similar checks from two callers that had them.
Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
(cherry picked from commit
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| .gitlab-ci | ||
| Xext | ||
| Xi | ||
| composite | ||
| config | ||
| damageext | ||
| dbe | ||
| dix | ||
| doc | ||
| dri3 | ||
| exa | ||
| fb | ||
| glamor | ||
| glx | ||
| hw | ||
| include | ||
| m4 | ||
| man | ||
| mi | ||
| miext | ||
| os | ||
| present | ||
| pseudoramiX | ||
| randr | ||
| record | ||
| render | ||
| test | ||
| xfixes | ||
| xkb | ||
| .appveyor.yml | ||
| .dir-locals.el | ||
| .gitignore | ||
| .gitlab-ci.yml | ||
| .travis.yml | ||
| COPYING | ||
| Makefile.am | ||
| README.md | ||
| autogen.sh | ||
| configure.ac | ||
| devbook.am | ||
| docbook.am | ||
| fix-miregion | ||
| fix-miregion-private | ||
| fix-patch-whitespace | ||
| fix-region | ||
| manpages.am | ||
| meson.build | ||
| meson_options.txt | ||
| xorg-server.m4 | ||
| xorg-server.pc.in | ||
| xserver.ent.in | ||
X Server
The X server accepts requests from client applications to create windows, which are (normally rectangular) "virtual screens" that the client program can draw into.
Windows are then composed on the actual screen by the X server (or by a separate composite manager) as directed by the window manager, which usually communicates with the user via graphical controls such as buttons and draggable titlebars and borders.
For a comprehensive overview of X Server and X Window System, consult the following article: https://en.wikipedia.org/wiki/X_server
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