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From: Stanislav German-Evtushenko <ginermail@gmail.com>
To: Guenter Roeck <linux@roeck-us.net>
Cc: Wim Van Sebroeck <wim@linux-watchdog.org>,
	"linux-watchdog@vger.kernel.org" <linux-watchdog@vger.kernel.org>
Subject: Re: [PATCH] watchdog: Device must be opened for writing
Date: Sun, 15 Aug 2021 04:32:13 +0000	[thread overview]
Message-ID: <CAPeRZrWeiQRWhVi5N2ho=RhvaSjR4NcMFGgewWkfM5tj+tSRaQ@mail.gmail.com> (raw)
In-Reply-To: <b9818198-48f1-c75e-2dbe-eabfc36b6725@roeck-us.net>

On 8/15/21, Guenter Roeck <linux@roeck-us.net> wrote:
> On 8/14/21 5:19 PM, Stanislav German-Evtushenko wrote:
>> On Saturday, August 14, 2021, Guenter Roeck <linux@roeck-us.net
>> <mailto:linux@roeck-us.net>> wrote:
>>  > On Sun, Aug 15, 2021 at 04:13:45AM +0900, Stanislav German-Evtushenko
>> wrote:
>>  >> If userspace opens the watchdog device self-feeding stops. Sometimes
>>  >> opening the device happens by accident, e.g. by mistakenly running
>> grep
>>  >> recursively in a wrong directory which leads to the server being
>> reset.
>>  >>
>>  >> Watchdog device does not handle read operation therefore the issue can
>> be
>>  >> prevented by requiring the device to be opened for writing:
>>  >>
>>  >> - Prevent opening the device without FMODE_WRITE
>>  >>
>>  >> Signed-off-by: Stanislav German-Evtushenko <ginermail@gmail.com
>> <mailto:ginermail@gmail.com>>
>>  >
>>  > NACK. That would be a major undocumented ABI change. Opening
>> /dev/watchdog
>>  > for reading can be and is used today to test a watchdog.
>>  >
>>  > Guenter
>>  >
>>
>> I see. This is unfortunate.
>>
>> In this case I'll try to find the right place in the documentation and
>> make it more explicit unless it is already there and I've overlooked.
>>
> No. That isn't the point. This is used and must not be changed.
> Again, people (including me( are _using_ this to test watchdogs.
> We are not going to disable that because some people are not
> careful when executing commands as root.
>
> Guenter
>

I mean I would describe the existing behavior as this is not obvious.

As for testing, opening for writing is not harder than for reading but
I understand that it would be a breaking change now.

      reply	other threads:[~2021-08-15  4:32 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-14 19:13 Stanislav German-Evtushenko
2021-08-14 19:56 ` Guenter Roeck
     [not found]   ` <CAPeRZrV+HwdmBKFB3tmG_tEHjsR8h3WLxKQYGDLOLgw178oq=A@mail.gmail.com>
2021-08-15  1:33     ` Guenter Roeck
2021-08-15  4:32       ` Stanislav German-Evtushenko [this message]

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