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Avoid invalid read in webgl1.c #20687

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Merged
sbc100 merged 1 commit into from
Nov 11, 2023
Merged

Avoid invalid read in webgl1.c #20687

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20 changes: 16 additions & 4 deletions system/lib/gl/webgl1.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
* University of Illinois/NCSA Open Source License. Both these licenses can be
* found in the LICENSE file.
*/
#include <assert.h>
#include <emscripten/threading.h>
#include <emscripten/console.h>
#include <string.h>
Expand All @@ -27,8 +28,20 @@ static void InitWebGLTls() {
pthread_key_create(&currentThreadOwnsItsWebGLContext, NULL);
}

static pthread_t GetCurrentTargetThread() {
return *(void**)(pthread_getspecific(currentActiveWebGLContext) + 4);
// When OFFSCREEN_FRAMEBUFFER is enabled the EMSCRIPTEN_WEBGL_CONTEXT_HANDLE
// is a pointer to a struct with two fields. See registerContext in
// library_webgl.js
typedef struct WebGLContextHandle {
uint32_t explicit_swap_control;
pthread_t owning_thread;
} WebGLContextHandle;

static inline pthread_t GetOwningThread(EMSCRIPTEN_WEBGL_CONTEXT_HANDLE handle) {
return ((WebGLContextHandle*)handle)->owning_thread;
}

static inline pthread_t GetCurrentTargetThread() {
return GetOwningThread(emscripten_webgl_get_current_context());
}

EMSCRIPTEN_WEBGL_CONTEXT_HANDLE emscripten_webgl_create_context(const char *target, const EmscriptenWebGLContextAttributes *attributes) {
Expand All @@ -54,8 +67,7 @@ EMSCRIPTEN_RESULT emscripten_webgl_make_context_current(EMSCRIPTEN_WEBGL_CONTEXT
if (emscripten_webgl_get_current_context() == context)
return EMSCRIPTEN_RESULT_SUCCESS;

void *owningThread = *(void**)(context + 4);
if (owningThread == pthread_self()) {
if (context && GetOwningThread(context) == pthread_self()) {
EMSCRIPTEN_RESULT r = emscripten_webgl_make_context_current_calling_thread(context);
if (r == EMSCRIPTEN_RESULT_SUCCESS) {
pthread_setspecific(currentActiveWebGLContext, (void*)context);
Expand Down