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[PLAT-6973] Fix stack overflow in +[BugsnagThread allThreadsWithCurrentThreadBacktrace:] #1148

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Jul 7, 2021
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[PLAT-6973] Fix stack overflow in +[BugsnagThread allThreadsWithCurrentThreadBacktrace:] #1148

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22 changes: 13 additions & 9 deletions Bugsnag/Payload/BugsnagThread.m
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Original file line number Diff line number Diff line change
Expand Up @@ -213,19 +213,23 @@ + (NSDictionary *)enhanceThreadInfo:(NSDictionary *)thread
thread_t *threads = NULL;
mach_msg_type_number_t threadCount = 0;

if (task_threads(mach_task_self(), &threads, &threadCount) != KERN_SUCCESS) {
return @[];
}

NSMutableArray *objects = [NSMutableArray arrayWithCapacity:threadCount];

struct backtrace_t *backtraces = calloc(threadCount, sizeof(struct backtrace_t));
if (!backtraces) {
goto cleanup;
}

suspend_threads();

// While threads are suspended only async-signal-safe functions should be used,
// as another threads may have been suspended while holding a lock in malloc,
// the Objective-C runtime, or other subsystems.

if (task_threads(mach_task_self(), &threads, &threadCount) != KERN_SUCCESS) {
resume_threads();
return @[];
}

struct backtrace_t backtraces[threadCount];

for (mach_msg_type_number_t i = 0; i < threadCount; i++) {
BOOL isCurrentThread = MACH_PORT_INDEX(threads[i]) == MACH_PORT_INDEX(bsg_ksmachthread_self());
if (isCurrentThread) {
Expand All @@ -237,8 +241,6 @@ + (NSDictionary *)enhanceThreadInfo:(NSDictionary *)thread

resume_threads();

NSMutableArray *objects = [NSMutableArray arrayWithCapacity:threadCount];

for (mach_msg_type_number_t i = 0; i < threadCount; i++) {
BOOL isCurrentThread = MACH_PORT_INDEX(threads[i]) == MACH_PORT_INDEX(bsg_ksmachthread_self());
struct backtrace_t *backtrace = isCurrentThread ? currentThreadBacktrace : &backtraces[i];
Expand All @@ -249,11 +251,13 @@ + (NSDictionary *)enhanceThreadInfo:(NSDictionary *)thread
index:i]];
}

cleanup:
for (mach_msg_type_number_t i = 0; i < threadCount; i++) {
mach_port_deallocate(mach_task_self(), threads[i]);
}
vm_deallocate(mach_task_self(), (vm_address_t)threads, sizeof(thread_t) * threadCount);

free(backtraces);
return objects;
}

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3 changes: 3 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -5,6 +5,9 @@ Changelog

### Bug fixes

* Fix a potential stack overflow in `+[BugsnagThread allThreadsWithCurrentThreadBacktrace:]`.
[#1148](https://github.com/bugsnag/bugsnag-cocoa/pull/1148)

* Fix `NSNull` handling in `+[BugsnagError errorFromJson:]` and `+[BugsnagStackframe frameFromJson:]`.
[#1143](https://github.com/bugsnag/bugsnag-cocoa/pull/1143)
[#1138](https://github.com/bugsnag/bugsnag-cocoa/issues/1138)
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20 changes: 20 additions & 0 deletions Tests/BugsnagThreadTests.m
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Expand Up @@ -222,6 +222,26 @@ - (void)testAllThreads {
XCTAssertGreaterThan(threads.count, 1);
}

- (void)testAllThreadsFromBackgroundDoesNotOverflowStack {
const int threadCount = 1000;
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
for (int i = 0; i < threadCount; i++) {
[NSThread detachNewThreadSelector:@selector(waitForSemaphore:) toTarget:self withObject:semaphore];
}
__block NSArray<BugsnagThread *> *threads = nil;
dispatch_sync(dispatch_get_global_queue(QOS_CLASS_USER_INITIATED, 0), ^{
threads = [BugsnagThread allThreads:YES callStackReturnAddresses:NSThread.callStackReturnAddresses];
});
XCTAssertGreaterThan(threads.count, threadCount);
for (int i = 0; i < threadCount; i++) {
dispatch_semaphore_signal(semaphore);
}
}

- (void)waitForSemaphore:(dispatch_semaphore_t)semaphore {
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
}

- (void)testCurrentThread {
NSArray<BugsnagThread *> *threads = [BugsnagThread allThreads:NO callStackReturnAddresses:NSThread.callStackReturnAddresses];
[threads[0].stacktrace makeObjectsPerformSelector:@selector(symbolicateIfNeeded)];
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