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Message-ID: <AM6PR03MB5170E9D0DB405EC051F7731CE4E30@AM6PR03MB5170.eurprd03.prod.outlook.com>
Date: Fri, 6 Mar 2020 19:16:08 +0000
From: Bernd Edlinger <bernd.edlinger@...mail.de>
To: "Eric W. Biederman" <ebiederm@...ssion.com>
CC: Christian Brauner <christian.brauner@...ntu.com>,
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Subject: Re: [PATCH 2/2] exec: Add a exec_update_mutex to replace
cred_guard_mutex
On 3/6/20 6:17 AM, Eric W. Biederman wrote:
> Bernd Edlinger <bernd.edlinger@...mail.de> writes:
>
>> On 3/5/20 10:16 PM, Eric W. Biederman wrote:
>>>
>>> The cred_guard_mutex is problematic. The cred_guard_mutex is held
>>> over the userspace accesses as the arguments from userspace are read.
>>> The cred_guard_mutex is held of PTRACE_EVENT_EXIT as the the other
>>> threads are killed. The cred_guard_mutex is held over
>>> "put_user(0, tsk->clear_child_tid)" in exit_mm().
>>>
I am all for this patch, and the direction it is heading, Eric.
I just wanted to add a note that I think it is
possible that exec_mm_release can also invoke put_user(0, tsk->clear_child_tid),
under the new exec_update_mutex, since vm_access increments the
mm->mm_users, under the cred_update_mutex, but releases the mutex,
and the caller can hold the reference for a while and then exec_mmap is not
releasing the last reference.
Bernd.
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