Re: [syzbot] [perf?] KASAN: slab-use-after-free Read in __uprobe_unregister

[Oleg Nesterov <oleg@redhat.com>]

On 08/11, Oleg Nesterov wrote:
>
> Hmm, bpf_uprobe_multi_link_attach() looks obviously wrong.
>
> bpf_link_prime() is called after the
>
> 	for (i = 0; i < cnt; i++) {
> 		uprobe_register(...);
> 		...
> 	}
>
> loop. If bpf_link_prime() fails, bpf_uprobe_multi_link_attach() just do
> kvfree(uprobes) without _unregister(). In particular, this leaks the freed
> bpf_uprobe->consumer in the uprobe->consumers list.
>
> After that another _unregister() on the same uprobe can hit the problem.
>
> I guess we need a simple patch for -stable...

Something like below on top of perf/core. But I don't like the usage of
"i" in the +error_unregister path...

Oleg.

--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3486,17 +3486,19 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 						    &uprobes[i].consumer);
 		if (IS_ERR(uprobes[i].uprobe)) {
 			err = PTR_ERR(uprobes[i].uprobe);
-			bpf_uprobe_unregister(uprobes, i);
-			goto error_free;
+			goto error_unregister;
 		}
 	}
 
 	err = bpf_link_prime(&link->link, &link_primer);
 	if (err)
-		goto error_free;
+		goto error_unregister;
 
 	return bpf_link_settle(&link_primer);
 
+error_unregister:
+	bpf_uprobe_unregister(uprobes, i);
+
 error_free:
 	kvfree(uprobes);
 	kfree(link);