posix: shm: offset should compare with the shm size

The read/write offset should have compared with the size of
the shm object, not the size of the buffer.

Signed-off-by: Yong Cong Sin <[email protected]>

Author: ycsin

lib/posix/options/shm.c

@@ -204,7 +204,7 @@ static int shm_mmap(struct shm_obj *shm, void *addr, size_t len, int prot, int f
 
 static ssize_t shm_rw(struct shm_obj *shm, void *buf, size_t size, bool is_write, size_t offset)
 {
-	if (offset >= size) {
+	if (offset >= shm->size) {
 		size = 0;
 	} else {
 		size = MIN(size, shm->size - offset);