From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E378445C0B; Fri, 17 Oct 2025 15:08:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760713730; cv=none; b=fSSjuIhu0IXzp7Ei8VmPPYGsJ8HtvN1QxIUWUOck445rgMFKU/e99IU6srH5Qg9/Bh5TV81/DAUVCLFQ2kpLeKhZUubQJttpef9OSjVe2ocXq5PVWzgRU9k2cZLRf0roCG2OT5t0pWtx/s7r17dUzG1V+NGG3o8rwoTlmaPYyng= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760713730; c=relaxed/simple; bh=zlN5XZLx7Vy0hhYh1hsTGvuv8lqAIgQYqfKTEdE4cjk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=XTuLY8XbggX2G4Eq8zXDhZKinWn+UOJT2VGMnVxkl03mQg17hqwXrVZm8MUrqjAdOSURjVi4WjLDgYUj3aQhwQBYTDiiRU5PhR2PuduYzqSPm2V/Toda9BzxCsYrk7FDP/movWY3Zu4ZGfzqtOUTPRgTamhjX7vL+HSsVsQYLLU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=yZ9ip/mH; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="yZ9ip/mH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6DE7FC4CEF9; Fri, 17 Oct 2025 15:08:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1760713729; bh=zlN5XZLx7Vy0hhYh1hsTGvuv8lqAIgQYqfKTEdE4cjk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=yZ9ip/mHTjkzr4nX6lOQfWhxSrIHOu639R8G2OQoaZMok5aIEk6HkR21Xu0JzF8K2 kCZ5wqUqaM2AIZ02oC+NUkd82bONQlaD455wh+N4Wyzfr+wkCbEjDVgsSwRgkDD4sW OsBjyNlnImDDiYRpThw2caslR201tGkRKFZALJ74= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Oleg Nesterov , Christian Brauner , Jiri Slaby , Mateusz Guzik , Andrew Morton Subject: [PATCH 6.6 099/201] kernel/sys.c: fix the racy usage of task_lock(tsk->group_leader) in sys_prlimit64() paths Date: Fri, 17 Oct 2025 16:52:40 +0200 Message-ID: <20251017145138.386170973@linuxfoundation.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251017145134.710337454@linuxfoundation.org> References: <20251017145134.710337454@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Oleg Nesterov commit a15f37a40145c986cdf289a4b88390f35efdecc4 upstream. The usage of task_lock(tsk->group_leader) in sys_prlimit64()->do_prlimit() path is very broken. sys_prlimit64() does get_task_struct(tsk) but this only protects task_struct itself. If tsk != current and tsk is not a leader, this process can exit/exec and task_lock(tsk->group_leader) may use the already freed task_struct. Another problem is that sys_prlimit64() can race with mt-exec which changes ->group_leader. In this case do_prlimit() may take the wrong lock, or (worse) ->group_leader may change between task_lock() and task_unlock(). Change sys_prlimit64() to take tasklist_lock when necessary. This is not nice, but I don't see a better fix for -stable. Link: https://lkml.kernel.org/r/20250915120917.GA27702@redhat.com Fixes: 18c91bb2d872 ("prlimit: do not grab the tasklist_lock") Signed-off-by: Oleg Nesterov Cc: Christian Brauner Cc: Jiri Slaby Cc: Mateusz Guzik Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- kernel/sys.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-) --- a/kernel/sys.c +++ b/kernel/sys.c @@ -1689,6 +1689,7 @@ SYSCALL_DEFINE4(prlimit64, pid_t, pid, u struct rlimit old, new; struct task_struct *tsk; unsigned int checkflags = 0; + bool need_tasklist; int ret; if (old_rlim) @@ -1715,8 +1716,25 @@ SYSCALL_DEFINE4(prlimit64, pid_t, pid, u get_task_struct(tsk); rcu_read_unlock(); - ret = do_prlimit(tsk, resource, new_rlim ? &new : NULL, - old_rlim ? &old : NULL); + need_tasklist = !same_thread_group(tsk, current); + if (need_tasklist) { + /* + * Ensure we can't race with group exit or de_thread(), + * so tsk->group_leader can't be freed or changed until + * read_unlock(tasklist_lock) below. + */ + read_lock(&tasklist_lock); + if (!pid_alive(tsk)) + ret = -ESRCH; + } + + if (!ret) { + ret = do_prlimit(tsk, resource, new_rlim ? &new : NULL, + old_rlim ? &old : NULL); + } + + if (need_tasklist) + read_unlock(&tasklist_lock); if (!ret && old_rlim) { rlim_to_rlim64(&old, &old64);