Re: [RFC][PATCH 00/20] Mount writer count and read-only bind mounts (v2)

[Jan Engelhardt <jengelh@linux01.gwdg.de>]

>> >I assume you're talking about this kind of situation:
>> >
>> >mount --bind /local/writable/dir /chroot/untrusted/area/
>> >mount --o remount,ro /chroot/untrusted/area/
>> 
>> Well, actually about some kind of VPS: openvz or something like that.
>> But yes, this is the same kind of scenario.
>
>yes, Linux-VServer provides this kind of ro --bind mounts
>without the race, as the the flags are passed on the actual
>mount
>
>> >This has no r/w window in the chroot area:
>> >
>> >mount --bind /local/writable/dir /tmp/area/
>> >mount --o remount,ro /tmp/area/
>> >mount --bind /tmp/area/ /chroot/untrusted/area/
>> >umount /tmp/area/
>> 
>> Well, it looks a little scarry and complicated at first. And probably
>> requires you to know that semantic of --bind lets you do the last
>> unmount. But if you are saying that this makes kernel smaller, faster
>> and less buggy then you are probably very right.
>
>well, it makes the kernel more consistant in it's behaviour,
>because especially for --rbind mounts, the logic what is
>changed where and when is not as well defined as one would
>wish ...
>
>btw, you could get the same result by simply doing:
>
>mount --bind /local/writable/dir /tmp/area/
>mount --o remount,ro /tmp/area/
>mount --move /tmp/area/ /chroot/untrusted/area/
>

Just a nitpick, you all use "--o" ... :)
mount: option `--o' is ambiguous




Jan Engelhardt
--