linux-kernel - Re: [PATCHv2 mm-stable] uprobes: Revert ref_ctr_offset in uprobe

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Message-ID: <e77b2fb5-f2ff-4c11-8b3a-6b5ee89738e0@redhat.com>
Date: Tue, 17 Jun 2025 13:59:50 +0200
From: David Hildenbrand <david@...hat.com>
To: Jiri Olsa <olsajiri@...il.com>, Masami Hiramatsu <mhiramat@...nel.org>,
 Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Andrii Nakryiko <andrii@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCHv2 mm-stable] uprobes: Revert ref_ctr_offset in
 uprobe_unregister error path

On 17.06.25 13:58, Jiri Olsa wrote:
> ping
> 
> On Wed, Jun 11, 2025 at 10:57:08AM +0200, Jiri Olsa wrote:
>> hi, ping ;-)
>>
>> On Wed, Jun 04, 2025 at 10:28:42PM +0200, Jiri Olsa wrote:
>>> On Wed, May 14, 2025 at 12:18:09PM +0200, Jiri Olsa wrote:
>>>> From: Jiri Olsa <olsajiri@...il.com>
>>>>
>>>> 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
>>>>
>>>> Fixes: 1cc33161a83d ("uprobes: Support SDT markers having reference count (semaphore)")
>>>> Acked-by: David Hildenbrand <david@...hat.com>
>>>> Acked-by: Oleg Nesterov <oleg@...hat.com>
>>>> Suggested-by: Oleg Nesterov <oleg@...hat.com>
>>>> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
>>>
>>> hi,
>>> I can't find this in any related tree, was this pulled in?

@Andrew, I assume you should pick this.

-- 
Cheers,

David / dhildenb