fprobe: Check rethook_alloc() return in rethook initialization

Check if fp->rethook succeeded to be allocated. Otherwise, if
rethook_alloc() fails, then we end up dereferencing a NULL pointer in
rethook_add_node().

Link: https://lore.kernel.org/all/[email protected]/

Fixes: 5b0ab78 ("fprobe: Add exit_handler support")
Cc: [email protected]
Signed-off-by: Rafael Mendonca <[email protected]>
Acked-by: Steven Rostedt (Google) <[email protected]>
Acked-by: Masami Hiramatsu (Google) <[email protected]>
Signed-off-by: Masami Hiramatsu (Google) <[email protected]>

Author: rafaelmsoares

kernel/trace/fprobe.c

@@ -141,6 +141,8 @@ static int fprobe_init_rethook(struct fprobe *fp, int num)
 		return -E2BIG;
 
 	fp->rethook = rethook_alloc((void *)fp, fprobe_exit_handler);
+	if (!fp->rethook)
+		return -ENOMEM;
 	for (i = 0; i < size; i++) {
 		struct fprobe_rethook_node *node;