linux-kernel - Re: [PATCH mm-stable] uprobes: Revert ref_ctr_offset 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: <60b3386e-dbb1-4fe9-bc38-d62eba4d9c50@redhat.com>
Date: Tue, 13 May 2025 15:16:08 +0200
From: David Hildenbrand <david@...hat.com>
To: Jiri Olsa <jolsa@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>,
 Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Andrii Nakryiko <andrii@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH mm-stable] uprobes: Revert ref_ctr_offset in
 uprobe_unregister error path

On 13.05.25 14:21, Jiri Olsa wrote:
> From: Jiri Olsa <olsajiri@...il.com>
> 

Thanks for debugging.

> There's error path that could lead to inactive uprobe:
> 
>    1) uprobe_register succeeds - updates instruction to int3 and
>       changes ref_ctr from 0 to 1
>    2) uprobe_unregister fails  - int3 stays in place, but ref_ctr
>       is changed to 0 (it's not restored to 1 in the fail path)
>       uprobe is leaked
>    3) another uprobe_register comes and re-uses the leaked uprobe
>       and succeds - but int3 is already in place, so ref_ctr update
>       is skipped and it stays 0 - uprobe CAN NOT be triggered now
>    4) uprobe_unregister fails because ref_ctr value is unexpected
> 
> Fixing this by reverting the updated ref_ctr value back to 1 in step 2),
> which is the case when uprobe_unregister fails (int3 stays in place),
> but we have already updated refctr.
> 
> The new scenario will go as follows:
> 
>    1) uprobe_register succeeds - updates instruction to int3 and
>       changes ref_ctr from 0 to 1
>    2) uprobe_unregister fails  - int3 stays in place and ref_ctr
>       is reverted to 1..  uprobe is leaked
>    3) another uprobe_register comes and re-uses the leaked uprobe
>       and succeds - but int3 is already in place, so ref_ctr update
>       is skipped and it stays 1 - uprobe CAN be triggered now
>    4) uprobe_unregister succeeds
> 
> Suggested-by: Oleg Nesterov <oleg@...hat.com>

If it's in mm-stable, we should have

Fixes: ...

here

> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
> Please note it's based on mm-stable branch, because it has the
> latest uprobe_write_opcode rewrite changes.
> 
>   kernel/events/uprobes.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 4c965ba77f9f..84ee7b590861 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -581,8 +581,8 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
>   
>   out:
>   	/* Revert back reference counter if instruction update failed. */
> -	if (ret < 0 && is_register && ref_ctr_updated)
> -		update_ref_ctr(uprobe, mm, -1);
> +	if (ret < 0 && ref_ctr_updated)
> +		update_ref_ctr(uprobe, mm, is_register ? -1 : 1);


Hm, but my patch essentially did here

         /* Revert back reference counter if instruction update failed. */
-       if (ret && is_register && ref_ctr_updated)
+       if (ret < 0 && is_register && ref_ctr_updated)
                 update_ref_ctr(uprobe, mm, -1);

So how come this wasn't a problem before?

-- 
Cheers,

David / dhildenb