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glx: Fix SEGV due to dereferencing a NULL ptr from XCB-GLX.

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When run in optirun, applications that linked to `libGLX.so` and then
proceeded to querying Mesa for extension strings caused a SEGV in Mesa.

`glXQueryExtensionsString` was calling a chain of functions that
eventually led to `__glXQueryServerString`. This function would call
`xcb_glx_query_server_string` then `xcb_glx_query_server_string_reply`.
The latter for some unknown reason returned `NULL`. Passing this `NULL`
to `xcb_glx_query_server_string_string_length` would cause a SEGV as the
function tried to dereference it.

The reason behind the function returning `NULL` is yet to be determined,
however, simply checking that the ptr is not `NULL` resolves this. A
similar check has been added to `__glXGetString` for completeness sake,
although not immediately necessary.

In addition to that, we stumbled into a similar problem in
`AllocAndFetchScreenConfigs` which tries to access the configs to free
them if `__glXQueryServerString` fails. This, of course, SEGVs, because the
configs are yet to have been allocated. Simply continuing past the configs
if their config ptrs are `NULL` resolves this. We also switch to `calloc`
to make sure that the config ptrs are `NULL` by default, and not some
uninitialized value.

Cc: mesa-stable@lists.freedesktop.org
Fixes: 24b8a8cfe8 "glx: implement __glXGetString, hide __glXGetStringFromServer"
Fixes: cb3610e37c "Import the GLX client side library, formerly from xc/lib/GL/glx. Build it "
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Hal Gentz <zegentzy@protonmail.com>
This commit is contained in:
Hal Gentz 2019-07-25 15:40:50 -06:00 • committed by Adam Jackson
parent 9acb94b623
commit 1591d1fee5
2 changed files with 9 additions and 1 deletions
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6
src/glx/glx_query.c
View file

@ -50,6 +50,9 @@ __glXQueryServerString(Display * dpy, int opcode, CARD32 screen, CARD32 name)
name),
NULL);
if (!reply)
return NULL;
/* The spec doesn't mention this, but the Xorg server replies with
* a string already terminated with '\0'. */
uint32_t len = xcb_glx_query_server_string_string_length(reply);
@ -74,6 +77,9 @@ __glXGetString(Display * dpy, int opcode, CARD32 contextTag, CARD32 name)
name),
NULL);
if (!reply)
return NULL;
/* The spec doesn't mention this, but the Xorg server replies with
* a string already terminated with '\0'. */
uint32_t len = xcb_glx_get_string_string_length(reply);

4
src/glx/glxext.c
View file

@ -214,6 +214,8 @@ FreeScreenConfigs(struct glx_display * priv)
screens = ScreenCount(priv->dpy);
for (i = 0; i < screens; i++) {
psc = priv->screens[i];
if (!psc)
continue;
glx_screen_cleanup(psc);
#if defined(GLX_DIRECT_RENDERING) && !defined(GLX_USE_APPLEGL)
@ -792,7 +794,7 @@ AllocAndFetchScreenConfigs(Display * dpy, struct glx_display * priv)
** First allocate memory for the array of per screen configs.
*/
screens = ScreenCount(dpy);
priv->screens = malloc(screens * sizeof *priv->screens);
priv->screens = calloc(screens, sizeof *priv->screens);
if (!priv->screens)
return GL_FALSE;