[Devel] Re: [PATCH 0/4] Devices accessibility control group (v2)

[Pavel Emelyanov]

sukadev at us.ibm.com wrote:
> | > I started playing with this and noticed that even if I try to
> | > enable read access to device [c, 1:3] it also grants access
> | > to device [c, 1:5]. 
> | 
> | Hm... I can't reproduce this:
> | 
> | # /bin/echo 'c 1:3 r-' > /cnt/dev/0/devices.permissions
> | # /bin/echo -n $$ > /cnt/dev/0/tasks
> | # cat /cnt/dev/0/devices.permissions 
> | c 1:3 r-
> | # hexdump /dev/null 
> | # hexdump /dev/zero 
> | hexdump: /dev/zero: No such device or address
> | hexdump: /dev/zero: Bad file descriptor
> | 
> | Maybe you have played with devs cgroups before getting this?
> | Can you show what's the contents of the devices.permissions file
> | in your case?
> 
> Here is the repro again. I even tried after a reboot. Basically,
> granting access to /dev/null is also granting access to /dev/zero.
> 
> 	# cat devices.permissions
> 	# hexdump /dev/zero
> 	hexdump: /dev/zero: No such device or address
> 	hexdump: /dev/zero: Bad file descriptor
> 	# hexdump /dev/null
> 	hexdump: /dev/null: No such device or address
> 	hexdump: /dev/null: Bad file descriptor
> 	# echo 'c 1:3 r-' > devices.permissions
> 	# hexdump /dev/null
> 	# hexdump /dev/zero
> 	0000000 0000 0000 0000 0000 0000 0000 0000 0000
> 	*
> 	^C
> 	# cat tasks
> 	3279
> 	22266
> 	# ps
> 	  PID TTY          TIME CMD
> 	 3279 pts/0    00:00:00 bash
> 	22267 pts/0    00:00:00 ps
> 

This all looks completely incomprehensible :( 

Here's my test:
# mount -t cgroup none /cnt/dev/ -o devices
# mkdir /cnt/dev/0
# /bin/echo -n $$ > /cnt/dev/0/tasks 
# cat /cnt/dev/0/devices.permissions 
# hexdump /dev/zero 
hexdump: /dev/zero: No such device or address
hexdump: /dev/zero: Bad file descriptor
# hexdump /dev/null 
hexdump: /dev/null: No such device or address
hexdump: /dev/null: Bad file descriptor
# echo 'c 1:3 r-' > /cnt/dev/0/devices.permissions
# cat /cnt/dev/0/devices.permissions 
c 1:3 r-
# hexdump /dev/null 
# hexdump /dev/zero 
hexdump: /dev/zero: No such device or address
hexdump: /dev/zero: Bad file descriptor


Sukadev, could you please try to track the problem as you
seem to be the only person who's experiencing problems
with that.

Thanks,
Pavel
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