On 07/03/2014 02:28 AM, Qu Wenruo wrote: > > -------- Original Message -------- > Subject: Re: [RFC PATCH] Revert "btrfs: allow mounting btrfs subvolumes with > different ro/rw options" > From: Goffredo Baroncelli <kreij...@libero.it> > To: Qu Wenruo <quwen...@cn.fujitsu.com>, linux-btrfs@vger.kernel.org > Date: 2014年07月03日 01:48 >> On 07/01/2014 11:30 AM, Qu Wenruo wrote: >>> This commit has the following problem: >>> 1) Break the ro mount rule. >>> When users mount the whole btrfs ro, it is still possible to mount >>> subvol rw and change the contents. Which make the whole fs ro mount >>> non-sense. >> Where is the problem ? I see an use case when I want a conservative default: >> mount all ro except some subvolumes. >> >> In any case it is not a security problem because if the user has the >> capability to mount a subvolume, also he has the capability to remount,rw >> the whole filesystem. >> >> >> > Not security problem but behavior not consistent. > If user mount the whole disk ro, he or she want the fs read only and nothing > will change in it. > If you mount a subvol rw, then the whole disk ro expectation is broken. > Things will change even the whole > disk is readonly.
Sorry for bother you again, but there is a thing not clear to me: If # mount -o subvolid=5,ro /dev/sda1 /mnt/root # mount -o subvol=subvolname,rw /dev/sda1 /mnt/subvolname I suppose that # touch /mnt/root/touch-test # 1 fails, and # touch /mnt/subvolname/touch-test # 2 succeeded. I understood correctly ? If so this behaviour seems to me correctly. Different is after mounting the subvolume "subvolumename", also the whole filesystem results rw (eg: #1 succeeded). G.Baroncelli > > The problem also happens when a parent subvol is mounted rw but child subvol > is mounted ro. > User can still modify the child subvol through parent subvol, still broke the > readonly rule. > > Thanks, > Qu > -- gpg @keyserver.linux.it: Goffredo Baroncelli (kreijackATinwind.it> Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html