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

[Oleg Nesterov]

On 08/11, Andrii Nakryiko wrote:
>
> On Sun, Aug 11, 2024 at 5:35 AM Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> >
> > Something like below on top of perf/core. But I don't like the usage of
> > "i" in the +error_unregister path...
> >
>
> Wouldn't the below be cleaner?
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index cd098846e251..3ca65454f888 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -3491,8 +3491,10 @@ int bpf_uprobe_multi_link_attach(const union
> bpf_attr *attr, struct bpf_prog *pr
>         }
>
>         err = bpf_link_prime(&link->link, &link_primer);
> -       if (err)
> +       if (err) {
> +               bpf_uprobe_unregister(&path, uprobes, cnt);

I disagree. This code already uses the "goto error_xxx" pattern, why
duplicate bpf_uprobe_unregister() ? What if another "can fail" code
comes between register and bpf_link_prime() ?

See the patch below, on top of perf/core.

> We should probably route this through the bpf tree, I don't think it
> will conflict with your changes, right?

It will conflict, and in this sense it is even worse than the "#syz test"
patch I sent in https://lore.kernel.org/all/20240811125816.GC30068@xxxxxxxxxx/

Because with your version above the necessary change

	-	bpf_uprobe_unregister(&path, uprobes, cnt);
	+	bpf_uprobe_unregister(uprobes, cnt);

won't be noticed during the merge, I guess.

So can we route this fix through the perf/core ? I'll add "cc: stable",
in the next merge window the Greg's scripts will report the "FAILED"
status of the -stable patch, I'll send the trivial backport in reply.

No?

Oleg.
---

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 4e391daafa64..90cd30e9723e 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3484,17 +3484,20 @@ 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;
+			link->cnt = i;
+			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, link->cnt);
+
 error_free:
 	kvfree(uprobes);
 	kfree(link);