linux-kernel - Re: [patch] fs, proc: truncate /proc/pid/comm writes to first TASK_COMM

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Date:	Tue, 09 Apr 2013 13:11:23 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	David Rientjes <rientjes@...gle.com>,
	John Stultz <johnstul@...ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [patch] fs, proc: truncate /proc/pid/comm writes to first TASK_COMM_LEN
 bytes

On 04/09/2013 01:03 PM, Andrew Morton wrote:
>> cc: John Stultz <johnstul@...ibm.com>
> I don't know if that address still works.

No, that email is no longer active. Thanks for noticing this.


> From: David Rientjes <rientjes@...gle.com>
> Subject: fs, proc: truncate /proc/pid/comm writes to first TASK_COMM_LEN bytes
>
> Currently, a write to a procfs file will return the number of bytes
> successfully written.  If the actual string is longer than this, the
> remainder of the string will not be be written and userspace will complete
> the operation by issuing additional write()s.
>
> Hence
>
> 	$ echo -n "abcdefghijklmnopqrs" > /proc/self/comm
>
> results in
>
> 	$ cat /proc/$$/comm
> 	pqrs
>
> since the final four bytes were written with a second write() since
> TASK_COMM_LEN == 16.  This is obviously an undesired result and not
> equivalent to prctl(PR_SET_NAME).  The implementation should not need to
> know the definition of TASK_COMM_LEN.

That's embarrassing, thanks for catching it!


> This patch truncates the string to the first TASK_COMM_LEN bytes and
> returns the bytes written as the length of the string written so the
> second write() is suppressed.
>
> 	$ cat /proc/$$/comm
> 	abcdefghijklmno
>
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> Cc: John Stultz <john.stultz@...aro.org>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>

Acked-by: John Stultz <john.stultz@...aro.org>
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