Re: [patch] fs, proc: truncate /proc/pid/comm writes to first TASK_COMM_LENbytes

From: John Stultz
Date: Tue Apr 09 2013 - 16:11:32 EST

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

No, that email is no longer active.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

From: David Rientjes <rientjes@xxxxxxxxxx>
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.


$ echo -n "abcdefghijklmnopqrs" > /proc/self/comm

results in

$ cat /proc/$$/comm

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

Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

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