bpf: Fix uprobe multi pid filter check

Uprobe multi link does its own process (thread leader) filtering before
running the bpf program by comparing task's vm pointers.

But as Oleg pointed out there can be processes sharing the vm (CLONE_VM),
so we can't just compare task->vm pointers, but instead we need to use
same_thread_group call.

Suggested-by: Oleg Nesterov <[email protected]>
Signed-off-by: Jiri Olsa <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Acked-by: Oleg Nesterov <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: olsajiri

kernel/trace/bpf_trace.c

@@ -3207,7 +3207,7 @@ static int uprobe_prog_run(struct bpf_uprobe *uprobe,
 	struct bpf_run_ctx *old_run_ctx;
 	int err = 0;
 
-	if (link->task && current->mm != link->task->mm)
+	if (link->task && !same_thread_group(current, link->task))
 		return 0;
 
 	if (sleepable)