Re: bizarre 2.6.8.1 /sys permissions

[Dave Jones]

On Wed, Aug 25, 2004 at 01:25:12PM -0700, Dan Hollis wrote:


 > Do these file permissions make sense to anyone?

Yes.

 > $ cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
 > cat: /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq: Permission denied

Reading this file causes reads from hardware on some cpufreq drivers.
This can be a slow operation, so a user could degrade system performance
for everyone else by repeatedly cat'ing it.

 > $ cat /proc/cpuinfo
 > processor       : 0
 > vendor_id       : GenuineIntel
 > cpu family      : 15
 > model           : 2
 > model name      : Intel(R) Celeron(R) CPU 2.60GHz
 > stepping        : 9
 > cpu MHz         : 324.528

This is read from the cpu_khz variable, so isn't affected by
this problem.

 > $ ls -la /sys/devices/system/cpu/cpu0/cpufreq/
 > total 0
 > drwxr-xr-x  2 root root    0 Aug 23 13:06 .
 > drwxr-xr-x  3 root root    0 Aug 23 13:06 ..
 > -r--------  1 root root 4096 Aug 23 13:06 cpuinfo_cur_freq
 > -r--r--r--  1 root root 4096 Aug 23 13:06 cpuinfo_max_freq
 > -r--r--r--  1 root root 4096 Aug 23 13:06 cpuinfo_min_freq
 > -r--r--r--  1 root root 4096 Aug 23 13:06 scaling_available_frequencies
 > -r--r--r--  1 root root 4096 Aug 23 13:06 scaling_available_governors
 > -r--r--r--  1 root root 4096 Aug 23 13:06 scaling_cur_freq
 > -r--r--r--  1 root root 4096 Aug 23 13:06 scaling_driver
 > -rw-r--r--  1 root root    0 Aug 25 13:19 scaling_governor
 > -rw-r--r--  1 root root 4096 Aug 23 13:06 scaling_max_freq
 > -rw-r--r--  1 root root 4096 Aug 23 13:06 scaling_min_freq
 > -rw-r--r--  1 root root    0 Aug 25 13:19 scaling_setspeed

Looks fine to me.

		Dave

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