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From: Jens Axboe <[email protected]>
To: Olivier Langlois <[email protected]>,
	"Eric W. Biederman" <[email protected]>,
	Linus Torvalds <[email protected]>
Cc: Linux Kernel Mailing List <[email protected]>,
	linux-fsdevel <[email protected]>,
	io-uring <[email protected]>,
	Alexander Viro <[email protected]>,
	"Pavel Begunkov>" <[email protected]>,
	Oleg Nesterov <[email protected]>
Subject: Re: [PATCH] coredump: Limit what can interrupt coredumps
Date: Sat, 12 Jun 2021 10:26:35 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 6/12/21 8:36 AM, Olivier Langlois wrote:
> On Thu, 2021-06-10 at 15:11 -0500, Eric W. Biederman wrote:
>>
>> Olivier Langlois has been struggling with coredumps being incompletely
>> written in
>> processes using io_uring.
>>
>> Olivier Langlois <[email protected]> writes:
>>> io_uring is a big user of task_work and any event that io_uring made
>>> a
>>> task waiting for that occurs during the core dump generation will
>>> generate a TIF_NOTIFY_SIGNAL.
>>>
>>> Here are the detailed steps of the problem:
>>> 1. io_uring calls vfs_poll() to install a task to a file wait queue
>>>    with io_async_wake() as the wakeup function cb from
>>> io_arm_poll_handler()
>>> 2. wakeup function ends up calling task_work_add() with TWA_SIGNAL
>>> 3. task_work_add() sets the TIF_NOTIFY_SIGNAL bit by calling
>>>    set_notify_signal()
>>
>> The coredump code deliberately supports being interrupted by SIGKILL,
>> and depends upon prepare_signal to filter out all other signals.   Now
>> that signal_pending includes wake ups for TIF_NOTIFY_SIGNAL this hack
>> in dump_emitted by the coredump code no longer works.
>>
>> Make the coredump code more robust by explicitly testing for all of
>> the wakeup conditions the coredump code supports.  This prevents
>> new wakeup conditions from breaking the coredump code, as well
>> as fixing the current issue.
>>
>> The filesystem code that the coredump code uses already limits
>> itself to only aborting on fatal_signal_pending.  So it should
>> not develop surprising wake-up reasons either.
>>
>> v2: Don't remove the now unnecessary code in prepare_signal.
>>
>> Cc: [email protected]
>> Fixes: 12db8b690010 ("entry: Add support for TIF_NOTIFY_SIGNAL")
>> Reported-by: Olivier Langlois <[email protected]>
>> Signed-off-by: "Eric W. Biederman" <[email protected]>
>> ---
>>  fs/coredump.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/coredump.c b/fs/coredump.c
>> index 2868e3e171ae..c3d8fc14b993 100644
>> --- a/fs/coredump.c
>> +++ b/fs/coredump.c
>> @@ -519,7 +519,7 @@ static bool dump_interrupted(void)
>>          * but then we need to teach dump_write() to restart and clear
>>          * TIF_SIGPENDING.
>>          */
>> -       return signal_pending(current);
>> +       return fatal_signal_pending(current) || freezing(current);
>>  }
>>  
>>  static void wait_for_dump_helpers(struct file *file)
> 
> Tested-by: Olivier Langlois <[email protected]>

Thanks Olivier and Eric for taking care of this. I've been mostly
offline for more than a week, back at it next week.

-- 
Jens Axboe


  reply	other threads:[~2021-06-12 16:27 UTC|newest]

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <[email protected]>
     [not found] ` <[email protected]>
     [not found]   ` <87h7i694ij.fsf_-_@disp2133>
2021-06-09 20:33     ` [RFC] coredump: Do not interrupt dump for TIF_NOTIFY_SIGNAL Linus Torvalds
2021-06-09 20:48       ` Eric W. Biederman
2021-06-09 20:52         ` Linus Torvalds
2021-06-09 21:02       ` Olivier Langlois
2021-06-09 21:05         ` Eric W. Biederman
2021-06-09 21:26           ` Olivier Langlois
2021-06-09 21:56             ` Olivier Langlois
2021-06-10 14:26             ` Eric W. Biederman
2021-06-10 15:17               ` Olivier Langlois
2021-06-10 18:58               ` [CFT}[PATCH] coredump: Limit what can interrupt coredumps Eric W. Biederman
2021-06-10 19:10                 ` Linus Torvalds
2021-06-10 19:18                   ` Eric W. Biederman
2021-06-10 19:50                     ` Linus Torvalds
2021-06-10 20:11                       ` [PATCH] " Eric W. Biederman
2021-06-10 21:04                         ` Linus Torvalds
2021-06-12 14:36                         ` Olivier Langlois
2021-06-12 16:26                           ` Jens Axboe [this message]
2021-06-14 14:10                         ` Oleg Nesterov
2021-06-14 16:37                           ` Eric W. Biederman
2021-06-14 16:59                             ` Oleg Nesterov
2021-06-15 22:08                           ` Eric W. Biederman
2021-06-16 19:23                             ` Olivier Langlois
2021-06-16 20:00                               ` Eric W. Biederman
2021-06-18 20:05                                 ` Olivier Langlois
2021-08-05 13:06                             ` Olivier Langlois
2021-08-10 21:48                               ` Tony Battersby
2021-08-11 20:47                                 ` Olivier Langlois
2021-08-12  1:55                                 ` Jens Axboe
2021-08-12 13:53                                   ` Tony Battersby
2021-08-15 20:42                                   ` Olivier Langlois
2021-08-16 13:02                                     ` Pavel Begunkov
2021-08-16 13:06                                       ` Pavel Begunkov
2021-08-17 18:15                                     ` Jens Axboe
2021-08-17 18:24                                       ` Jens Axboe
2021-08-17 19:29                                         ` Tony Battersby
2021-08-17 19:59                                           ` Jens Axboe
2021-08-17 21:28                                             ` Jens Axboe
2021-08-17 21:39                                               ` Tony Battersby
2021-08-17 22:05                                                 ` Jens Axboe
2021-08-18 14:37                                                   ` Tony Battersby
2021-08-18 14:46                                                     ` Jens Axboe
2021-08-18  2:57                                               ` Jens Axboe
2021-08-18  2:58                                                 ` Jens Axboe
2021-08-21 10:08                                                 ` Olivier Langlois
2021-08-21 16:47                                                   ` Olivier Langlois
2021-08-21 16:51                                                     ` Jens Axboe
2021-08-21 17:21                                                       ` Olivier Langlois
2021-08-21  9:52                                         ` Olivier Langlois
2021-08-21  9:48                                       ` Olivier Langlois
2021-10-22 14:13     ` [RFC] coredump: Do not interrupt dump for TIF_NOTIFY_SIGNAL Pavel Begunkov
2021-12-24  1:34       ` Olivier Langlois
2021-12-24 10:37         ` Pavel Begunkov
2021-12-24 19:52           ` Eric W. Biederman
2021-12-28 11:24             ` Pavel Begunkov
2022-03-14 23:58               ` Eric W. Biederman
     [not found]                 ` <[email protected]>
2022-06-01  3:15                   ` Jens Axboe
2022-07-20 16:49                     ` [PATCH 0/2] coredump: Allow io_uring using apps to dump to pipes Eric W. Biederman
2022-07-20 16:50                       ` [PATCH 1/2] signal: Move stopping for the coredump from do_exit into get_signal Eric W. Biederman
2022-07-20 16:51                       ` [PATCH 2/2] coredump: Allow coredumps to pipes to work with io_uring Eric W. Biederman
2022-08-22 21:16                         ` Olivier Langlois
2022-08-23  3:35                           ` Olivier Langlois
2022-08-23 18:22                             ` Eric W. Biederman
2022-08-23 18:27                               ` Jens Axboe
2022-08-24 15:11                                 ` Eric W. Biederman
2022-08-24 15:51                                   ` Jens Axboe
2022-01-05 19:39           ` [RFC] coredump: Do not interrupt dump for TIF_NOTIFY_SIGNAL Olivier Langlois

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