LibPthread: Ensure we're not overflowing the semaphore's value

Author: https://github.com/gunnarbeutner
Commit: 98403eccb0
Pull-request: https://github.com/SerenityOS/serenity/pull/6332
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/alimpfard
Reviewed-by: https://github.com/tomuta

Userland/Libraries/LibPthread/semaphore.cpp

@@ -48,8 +48,15 @@ int sem_getvalue(sem_t*, int*)
 
 int sem_init(sem_t* sem, int shared, unsigned int value)
 {
-    if (shared)
-        return ENOSYS;
+    if (shared) {
+        errno = ENOSYS;
+        return -1;
+    }
+
+    if (value > SEM_VALUE_MAX) {
+        errno = EINVAL;
+        return -1;
+    }
 
     if (pthread_mutex_init(&sem->mtx, nullptr) != 0)
         return -1;
@@ -70,6 +77,12 @@ sem_t* sem_open(const char*, int, ...)
 
 int sem_post(sem_t* sem)
 {
+    if (sem->value == SEM_VALUE_MAX) {
+        pthread_mutex_unlock(&sem->mtx);
+        errno = EOVERFLOW;
+        return -1;
+    }
+
     sem->value++;
 
     pthread_cond_signal(&sem->cv);

Userland/Libraries/LibPthread/semaphore.h

@@ -26,6 +26,7 @@
 
 #pragma once
 
+#include <limits.h>
 #include <pthread.h>
 #include <sys/cdefs.h>
 #include <sys/types.h>
@@ -48,4 +49,6 @@ int sem_trywait(sem_t*);
 int sem_unlink(const char*);
 int sem_wait(sem_t*);
 
+#define SEM_VALUE_MAX INT_MAX
+
 __END_DECLS