From: Bernd Edlinger <bernd.edlinger@hotmail.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Alexey Gladkov <gladkov.alexey@gmail.com>
Subject: Re: [GIT PULL] Please pull proc and exec work for 5.7-rc1
Date: Sat, 4 Apr 2020 07:43:42 +0200 [thread overview]
Message-ID: <AM6PR03MB517004C9D4F4E39816E926D9E4C40@AM6PR03MB5170.eurprd03.prod.outlook.com> (raw)
In-Reply-To: <CAHk-=wjqNnpsBJR1xM_Ce91cNh=24CDt6ibpL2G=vDUbSFGR8g@mail.gmail.com>
On 4/3/20 6:23 PM, Linus Torvalds wrote:
> On Fri, Apr 3, 2020 at 8:09 AM Bernd Edlinger <bernd.edlinger@hotmail.de> wrote:
>>
>> On 4/2/20 9:04 PM, Linus Torvalds wrote:
>>> In fact, then you could drop the
>>>
>>> mutex_unlock(&tsk->signal->exec_update_mutex);
>>>
>>> in the error case of exec_mmap(), because now the error handling in
>>> free_bprm() would do the cleanup automatically.
>>>
>>
>> The error handling is sometimes called when the exec_update_mutex is
>> not taken, in fact even de_thread not called.
>
> But that's the whole point of the flag. Make the flag be about "do I
> hold the mutex", and then the error handling does the right thing
> regardless.
>
>> Can you say how you would suggest that to be done?
>
> I think the easiest thing to do to explain is to just write the patch.
>
> This is entirely untested, but see what the difference is? I make the
> flag be about exactly where I take the lock, not about some "I have
> called exec_mmap".
>
> Which means that now exec_mmap() doesn't even need to unlock it in the
> error case, because the unlocking will happen properly in the
> bprm_exit regardless.
>
> This makes that unconditional unlocking logic much more obvious.
>
> That said, Eric says he can make it all properly static so that it
> doesn't need that kind of dynamic "if (x) unlock()" logic at all,
> which is much better.
>
> So this patch is not for consumption, it's purely for "look, something
> like this"
>
Just one suggestion, in general It would feel pretty much okay if you
like to improve the naming, and the consistency in any of my patches.
> @@ -1067,7 +1069,6 @@ static int exec_mmap(struct mm_struct *mm)
> down_read(&old_mm->mmap_sem);
> if (unlikely(old_mm->core_state)) {
> up_read(&old_mm->mmap_sem);
> - mutex_unlock(&tsk->signal->exec_update_mutex);
I was trying to replicate the behavior of prepare_bprm_creds
which also unlocks the mutex in the error case, therefore it felt
okay to unlock the mutex here, but it will work either way.
I should further note, that the mutex would be locked if this
error exit is taken, and unlocked if this error happens:
ret = mutex_lock_killable(&tsk->signal->exec_update_mutex);
if (ret)
return ret;
so at least the function comment I introduced above should be updated:
* Maps the mm_struct mm into the current task struct.
* On success, this function returns with the mutex
* exec_update_mutex locked.
> put_binfmt(fmt);
> - if (retval < 0 && bprm->called_exec_mmap) {
> + if (retval < 0 && !bprm->mm) {
Using bprm->mm like this feels like a hack to me. It works here,
but nowhere else. Therefore I changed this line.
Using !bprm->mm in the error handling code made Eric's patch fail.
Thanks
Bernd.
> Linus
>
next prev parent reply other threads:[~2020-04-04 5:44 UTC|newest]
Thread overview: 127+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <87blobnq02.fsf@x220.int.ebiederm.org>
2020-04-02 19:04 ` [GIT PULL] Please pull proc and exec work for 5.7-rc1 Linus Torvalds
2020-04-02 19:31 ` Bernd Edlinger
2020-04-02 19:52 ` Linus Torvalds
2020-04-02 20:59 ` Bernd Edlinger
2020-04-02 21:46 ` Linus Torvalds
2020-04-02 23:01 ` Eric W. Biederman
2020-04-02 23:42 ` Bernd Edlinger
2020-04-02 23:45 ` Eric W. Biederman
2020-04-02 23:49 ` Bernd Edlinger
2020-04-02 23:45 ` Linus Torvalds
2020-04-02 23:44 ` Linus Torvalds
2020-04-03 0:05 ` Eric W. Biederman
2020-04-07 1:29 ` [RFC][PATCH 0/3] exec_update_mutex related cleanups Eric W. Biederman
2020-04-07 1:31 ` [PATCH 1/3] binfmt: Move install_exec_creds after setup_new_exec to match binfmt_elf Eric W. Biederman
2020-04-07 15:58 ` Kees Cook
2020-04-07 16:11 ` Christian Brauner
2020-04-08 17:25 ` Linus Torvalds
2020-04-08 19:51 ` Eric W. Biederman
2020-04-07 1:31 ` [PATCH 2/3] exec: Make unlocking exec_update_mutex explict Eric W. Biederman
2020-04-07 16:02 ` Kees Cook
2020-04-07 16:17 ` Christian Brauner
2020-04-07 16:21 ` Eric W. Biederman
2020-04-07 1:32 ` [PATCH 3/3] exec: Rename the flag called_exec_mmap point_of_no_return Eric W. Biederman
2020-04-07 16:03 ` Kees Cook
2020-04-07 16:21 ` Christian Brauner
2020-04-07 16:22 ` [RFC][PATCH 0/3] exec_update_mutex related cleanups Christian Brauner
2020-04-08 17:26 ` Linus Torvalds
2020-04-03 5:09 ` [GIT PULL] Please pull proc and exec work for 5.7-rc1 Bernd Edlinger
2020-04-03 19:26 ` Linus Torvalds
2020-04-03 20:41 ` Waiman Long
2020-04-03 20:59 ` Linus Torvalds
2020-04-03 23:16 ` Waiman Long
2020-04-03 23:23 ` Waiman Long
2020-04-04 1:30 ` Linus Torvalds
2020-04-04 2:02 ` Waiman Long
2020-04-04 2:28 ` Linus Torvalds
2020-04-04 6:34 ` Bernd Edlinger
2020-04-05 6:34 ` Bernd Edlinger
2020-04-05 19:35 ` Linus Torvalds
2020-04-05 2:42 ` Waiman Long
2020-04-05 3:35 ` Bernd Edlinger
2020-04-05 3:45 ` Waiman Long
2020-04-06 13:13 ` Will Deacon
2020-04-04 4:23 ` Bernd Edlinger
2020-04-06 22:17 ` Eric W. Biederman
2020-04-07 19:50 ` Linus Torvalds
2020-04-07 20:29 ` Bernd Edlinger
2020-04-07 20:47 ` Linus Torvalds
2020-04-08 15:14 ` Eric W. Biederman
2020-04-08 15:21 ` Bernd Edlinger
2020-04-08 16:34 ` Linus Torvalds
2020-04-09 14:58 ` Eric W. Biederman
2020-04-09 15:15 ` Bernd Edlinger
2020-04-09 16:15 ` Linus Torvalds
2020-04-09 16:24 ` Linus Torvalds
2020-04-09 17:03 ` Eric W. Biederman
2020-04-09 17:17 ` Bernd Edlinger
2020-04-09 17:37 ` Linus Torvalds
2020-04-09 17:46 ` Bernd Edlinger
2020-04-09 18:36 ` Linus Torvalds
2020-04-09 19:42 ` Linus Torvalds
2020-04-09 19:57 ` Bernd Edlinger
2020-04-09 20:04 ` Linus Torvalds
2020-04-09 20:36 ` Bernd Edlinger
2020-04-09 21:00 ` Eric W. Biederman
2020-04-09 21:17 ` Linus Torvalds
2020-04-09 23:52 ` Bernd Edlinger
2020-04-10 0:30 ` Linus Torvalds
2020-04-10 0:32 ` Linus Torvalds
2020-04-11 4:07 ` Bernd Edlinger
2020-04-11 18:20 ` Oleg Nesterov
2020-04-11 18:29 ` Linus Torvalds
2020-04-11 18:31 ` Linus Torvalds
2020-04-11 19:15 ` Bernd Edlinger
2020-04-11 20:07 ` Linus Torvalds
2020-04-11 21:16 ` Bernd Edlinger
[not found] ` <CAHk-=wgWHkBzFazWJj57emHPd3Dg9SZHaZqoO7-AD+UbBTJgig@mail.gmail.com>
2020-04-11 21:57 ` Linus Torvalds
2020-04-12 6:01 ` Bernd Edlinger
2020-04-12 19:50 ` Oleg Nesterov
2020-04-12 20:14 ` Linus Torvalds
2020-04-28 2:56 ` Bernd Edlinger
2020-04-28 17:07 ` Linus Torvalds
2020-04-28 19:08 ` Oleg Nesterov
2020-04-28 20:35 ` Linus Torvalds
2020-04-28 21:06 ` Jann Horn
2020-04-28 21:36 ` Linus Torvalds
2020-04-28 21:53 ` Jann Horn
2020-04-28 22:14 ` Linus Torvalds
2020-04-28 23:36 ` Jann Horn
2020-04-29 17:58 ` Linus Torvalds
2020-04-29 18:33 ` Jann Horn
2020-04-29 18:57 ` Linus Torvalds
2020-04-29 19:23 ` Bernd Edlinger
2020-04-29 19:26 ` Jann Horn
2020-04-29 20:19 ` Bernd Edlinger
2020-04-29 21:06 ` Jann Horn
2020-04-29 22:38 ` Linus Torvalds
2020-04-29 23:22 ` Linus Torvalds
2020-04-29 23:59 ` Jann Horn
2020-04-30 1:08 ` Bernd Edlinger
2020-04-30 2:20 ` Linus Torvalds
2020-04-30 3:00 ` Jann Horn
2020-04-30 3:25 ` Linus Torvalds
2020-04-30 3:41 ` Jann Horn
2020-04-30 3:50 ` Linus Torvalds
2020-04-30 13:37 ` Linus Torvalds
2020-04-30 2:16 ` Linus Torvalds
2020-04-30 13:39 ` Bernd Edlinger
2020-04-30 13:47 ` Linus Torvalds
2020-04-30 14:29 ` Bernd Edlinger
2020-04-30 16:40 ` Linus Torvalds
2020-05-02 4:11 ` Bernd Edlinger
2020-04-09 17:36 ` Linus Torvalds
2020-04-09 20:34 ` Eric W. Biederman
2020-04-09 20:56 ` Linus Torvalds
2020-04-02 23:02 ` Bernd Edlinger
2020-04-02 23:22 ` Bernd Edlinger
2020-04-03 7:38 ` Bernd Edlinger
2020-04-03 16:00 ` Bernd Edlinger
2020-04-03 15:09 ` Bernd Edlinger
2020-04-03 16:23 ` Linus Torvalds
2020-04-03 16:36 ` Bernd Edlinger
2020-04-04 5:43 ` Bernd Edlinger [this message]
2020-04-04 5:48 ` Bernd Edlinger
2020-04-06 6:41 ` Bernd Edlinger
2020-04-10 13:03 ` [GIT PULL] proc fix " Eric W. Biederman
2020-04-10 20:40 ` pr-tracker-bot
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