linux-kernel - 3.3 and hidepid feature problem - options not always applied at mount

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Message-Id: <201203220903.15360.a.miskiewicz@gmail.com>
Date:	Thu, 22 Mar 2012 09:03:15 +0100
From:	Arkadiusz Miśkiewicz <a.miskiewicz@...il.com>
To:	Vasiliy Kulikov <segooon@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: 3.3 and hidepid feature problem - options not always applied at mount


Hi,

I'm trying to use hidepid feature in 3.3 kernel but I'm getting weird
things like options not being applied _sometimes_ at mount.

[@ ~]# cat /proc/mounts
sh: cat: /proc/mounts: No such file or directory
[@ ~]# strace -e mount -f -F -s 200 mount none /proc -t proc -o hidepid=2,gid=17                            
mount("none", "/proc", "proc", MS_MGC_VAL, "hidepid=2,gid=17") = 0
[@ ~]# cat /proc/mounts
rootfs / rootfs rw 0 0
/dev/sda3 / xfs rw,relatime,attr2,noquota 0 0
run /run tmpfs rw,relatime 0 0
none /proc proc rw,relatime 0 0

No hidepid, no gid - huh?

[@ ~]# mount /proc -o remount,hidepid=2,gid=17
[@ ~]# cat /proc/mounts
rootfs / rootfs rw 0 0
/dev/sda3 / xfs rw,relatime,attr2,noquota 0 0
run /run tmpfs rw,relatime 0 0
none /proc proc rw,relatime,gid=17,hidepid=2 0 0

remount and hidepid/gid is there

[@ ~]# umount /proc
[@ ~]# strace -e mount -f -F -s 200 mount none /proc -t proc -o hidepid=2,gid=17                            
mount("none", "/proc", "proc", MS_MGC_VAL, "hidepid=2,gid=17") = 0
[@ ~]# cat /proc/mounts
rootfs / rootfs rw 0 0
/dev/sda3 / xfs rw,relatime,attr2,noquota 0 0
run /run tmpfs rw,relatime 0 0
none /proc proc rw,relatime,gid=17,hidepid=2 0 0

and now I'm lost - every new umount & mount gets hidepid/gid right.

Any ideas why initial mount fails to get hidepid/gid options applied?
The syscall seems correct.
-- 
Arkadiusz Miśkiewicz        PLD/Linux Team
arekm / maven.pl            http://ftp.pld-linux.org/
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