From: "Eric W. Biederman" <ebiederm@xmission.com>
To: Bernd Edlinger <bernd.edlinger@hotmail.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
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Cyrill Gorcunov <gorcunov@gmail.com>,
Eric Dumazet <edumazet@google.com>
Subject: Re: [PATCH v18] exec: Fix dead-lock in de_thread with ptrace_attach
Date: Thu, 20 Nov 2025 09:15:57 -0600 [thread overview]
Message-ID: <87tsyozqdu.fsf@email.froward.int.ebiederm.org> (raw)
In-Reply-To: <GV2PPF74270EBEEE807D016A79FE7A2F463E4D6A@GV2PPF74270EBEE.EURP195.PROD.OUTLOOK.COM> (Bernd Edlinger's message of "Tue, 18 Nov 2025 19:13:33 +0100")
Bernd Edlinger <bernd.edlinger@hotmail.de> writes:
> This introduces signal->exec_bprm, which is used to
> fix the case when at least one of the sibling threads
> is traced, and therefore the trace process may dead-lock
> in ptrace_attach, but de_thread will need to wait for the
> tracer to continue execution.
A small quibble it isn't a dead lock. It isn't even really a live lock,
as it is possible to SIGKILL our way out.
Thinking about this there is a really silly and simple way we can deal
with this situation for PTRACE_ATTACH. We can send SIGSTOP and wait for
the thread to stop before doing anything with cred_guard_mutex.
PTRACE_ATTACH already implies sending SIGSTOP so as long as we have
enough permissions to send SIGSTOP I don't see that being a problem.
The worst case I can see is that we get a case where we stop the
process, the permission check fails under cred_guard_mutex and
and ptrace attach has fails and has to send SIGCONT to undo it's
premature SIGSTOP. That might almost be visible, but it would still
be legitimate because we can still check that we have permission to
send SIGSTOP.
Eric
next prev parent reply other threads:[~2025-11-20 16:07 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <AM8PR10MB470801D01A0CF24BC32C25E7E40E9@AM8PR10MB4708.EURPRD10.PROD.OUTLOOK.COM>
[not found] ` <AM8PR10MB470875B22B4C08BEAEC3F77FE4169@AM8PR10MB4708.EURPRD10.PROD.OUTLOOK.COM>
2023-10-30 5:20 ` [PATCH v12] exec: Fix dead-lock in de_thread with ptrace_attach Bernd Edlinger
2023-10-30 9:00 ` kernel test robot
2023-11-06 6:41 ` [PATCH v13] " Bernd Edlinger
2024-01-15 19:22 ` [PATCH v14] " Bernd Edlinger
2024-01-15 19:37 ` Matthew Wilcox
2024-01-17 9:51 ` Bernd Edlinger
2024-01-16 15:22 ` Oleg Nesterov
2024-01-17 15:07 ` Bernd Edlinger
2024-01-17 16:38 ` Oleg Nesterov
2024-01-22 13:24 ` Bernd Edlinger
2024-01-22 13:44 ` Oleg Nesterov
2024-01-22 21:30 ` Kees Cook
2024-01-23 18:30 ` Bernd Edlinger
2024-01-24 0:09 ` Kees Cook
2024-01-22 18:31 ` [PATCH v15] " Bernd Edlinger
2025-08-18 6:04 ` Jain, Ayush
2025-08-18 20:53 ` [PATCH v16] " Bernd Edlinger
2025-08-19 4:36 ` Kees Cook
2025-08-19 18:53 ` Bernd Edlinger
2025-08-21 17:34 ` [PATCH v17] " Bernd Edlinger
2025-10-27 6:26 ` Bernd Edlinger
2025-10-27 12:06 ` Peter Zijlstra
2025-11-02 16:17 ` Oleg Nesterov
2025-11-05 14:32 ` Oleg Nesterov
2025-11-11 9:21 ` Christian Brauner
2025-11-11 11:07 ` Bernd Edlinger
2025-11-11 13:12 ` Oleg Nesterov
2025-11-11 13:45 ` Bernd Edlinger
2025-11-12 9:52 ` Oleg Nesterov
2025-11-17 6:31 ` Bernd Edlinger
2025-11-17 15:01 ` Oleg Nesterov
2025-11-17 20:08 ` Bernd Edlinger
2025-11-23 18:32 ` Oleg Nesterov
2025-11-29 15:06 ` Bernd Edlinger
2025-12-01 15:13 ` Oleg Nesterov
2025-11-09 17:14 ` [RFC PATCH 0/3] mt-exec: fix deadlock with ptrace_attach() Oleg Nesterov
2025-11-09 17:14 ` [RFC PATCH 1/3] exec: make setup_new_exec() return int Oleg Nesterov
2025-11-09 17:15 ` [RFC PATCH 2/3] exec: don't wait for zombie threads with cred_guard_mutex held Oleg Nesterov
2025-11-10 10:58 ` Cyrill Gorcunov
2025-11-10 15:09 ` Oleg Nesterov
2025-11-10 21:49 ` Cyrill Gorcunov
2025-11-11 14:09 ` Oleg Nesterov
2025-11-09 17:16 ` [RFC PATCH 3/3] ptrace: ensure PTRACE_EVENT_EXIT won't stop if the tracee is killed by exec Oleg Nesterov
2025-11-10 5:28 ` [RFC PATCH 0/3] mt-exec: fix deadlock with ptrace_attach() Bernd Edlinger
2025-11-10 14:47 ` Oleg Nesterov
2025-11-18 18:13 ` [PATCH v18] exec: Fix dead-lock in de_thread with ptrace_attach Bernd Edlinger
2025-11-20 15:15 ` Eric W. Biederman [this message]
2025-11-20 17:29 ` Eric W. Biederman
2025-11-20 20:57 ` [RFC][PATCH] exec: Move cred computation under exec_update_lock Eric W. Biederman
2025-11-20 23:50 ` Eric W. Biederman
2025-11-21 2:59 ` Bernd Edlinger
2025-11-21 7:18 ` Eric W. Biederman
2025-11-21 9:35 ` Bernd Edlinger
2025-11-21 11:26 ` Bernd Edlinger
2025-11-21 19:19 ` Eric W. Biederman
2025-11-21 23:06 ` Ryan Lee
2025-11-23 18:52 ` Oleg Nesterov
2025-11-23 23:22 ` Eric W. Biederman
2025-11-25 16:19 ` Bernd Edlinger
2025-11-25 11:55 ` Roberto Sassu
2025-12-01 16:06 ` Are setuid shell scripts safe? (Implied by security_bprm_creds_for_exec) Eric W. Biederman
2025-12-01 16:49 ` Roberto Sassu
2025-12-01 18:53 ` Eric W. Biederman
2025-12-01 21:39 ` David Laight
2025-12-03 13:16 ` Bernd Edlinger
2025-12-04 5:49 ` Al Viro
2025-12-04 9:32 ` David Laight
2025-12-04 13:03 ` Bernd Edlinger
2025-12-09 12:28 ` Jan Kara
2025-12-04 15:43 ` Stephen Smalley
2025-11-22 17:10 ` [PATCH v18] exec: Fix dead-lock in de_thread with ptrace_attach Bernd Edlinger
2025-12-19 8:15 ` [PATCH v19] " Bernd Edlinger
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