linux-kernel - Re: [syzbot] [perf?] KASAN: slab-use-after-free Read in __uprobe

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAEf4BzZ6coCZHY_KMnSQQUyc_-xziKurOQ0j3xaCvHhnDaafuQ@mail.gmail.com>
Date: Mon, 12 Aug 2024 08:22:37 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: syzbot <syzbot+f7a1c2c2711e4a780f19@...kaller.appspotmail.com>, 
	Andrii Nakryiko <andrii@...nel.org>, jolsa@...nel.org, acme@...nel.org, 
	adrian.hunter@...el.com, alexander.shishkin@...ux.intel.com, 
	irogers@...gle.com, kan.liang@...ux.intel.com, linux-kernel@...r.kernel.org, 
	linux-perf-users@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	mark.rutland@....com, mhiramat@...nel.org, mingo@...hat.com, 
	namhyung@...nel.org, peterz@...radead.org, syzkaller-bugs@...glegroups.com, 
	bpf <bpf@...r.kernel.org>
Subject: Re: [syzbot] [perf?] KASAN: slab-use-after-free Read in __uprobe_unregister

adding bpf ML, given it's bpf's code base

On Mon, Aug 12, 2024 at 3:00 AM Oleg Nesterov <oleg@...hat.com> wrote:
>
> On 08/11, Andrii Nakryiko wrote:
> >
> > On Sun, Aug 11, 2024 at 5:35 AM Oleg Nesterov <oleg@...hat.com> 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

Well, if you have strong preferences, so be it (it's too trivial code
to argue about). We do have quite a lot of "hybrid" error handling
code that combines undoing the last step (especially if it's a simple
function call) and then doing goto for the rest of common error
handling, so I didn't (and still don't) see any problem with that.

> 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@redhat.com/
>
> 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.
>

Yeah, my bad, I forgot that the signature of bpf_uprobe_unregister()
also changed with your patches.

> 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.

Yep, absolutely, given the bpf_uprobe_unregister() change, I don't see
any problem for it to go together with your refactorings.

For the fix:

Acked-by: Andrii Nakryiko <andrii@...nel.org>

>
> 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);
>