On Tue, Jun 8, 2021 at 5:49 PM Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > > On Tue, 8 Jun 2021 at 16:37, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > > > On Tue, Jun 8, 2021 at 4:52 PM Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > > > > > > On Sun, 6 Jun 2021 at 16:46, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > > > > > > > When a lower file has immutable/append-only attributes, the behavior of > > > > overlayfs post copy up is inconsistent. > > > > > > > > Immediattely after copy up, ovl inode still has the S_IMMUTABLE/S_APPEND > > > > inode flags copied from lower inode, so vfs code still treats the ovl > > > > inode as immutable/append-only. After ovl inode evict or mount cycle, > > > > the ovl inode does not have these inode flags anymore. > > > > > > > > We cannot copy up the immutable and append-only fileattr flags, because > > > > immutable/append-only inodes cannot be linked and because overlayfs will > > > > not be able to set overlay.* xattr on the upper inodes. > > > > > > Ugh. > > > > > > > Instead, if any of the fileattr flags of interest exist on the lower > > > > inode, we set an xattr overlay.xflags on the upper inode as an indication > > > > to merge the origin inode fileattr flags on lookup. > > > > > > > > This gives consistent behavior post copy up regardless of inode eviction > > > > from cache. > > > > > > > > When user sets new fileattr flags, we break the connection with the > > > > origin fileattr by removing the overlay.xflags xattr. > > > > > > > > Note that having the S_IMMUTABLE/S_APPEND on the ovl inode does not > > > > provide the same level of protection as setting those flags on the real > > > > upper inode, because some filesystem check those flags internally in > > > > addition or instead of the vfs checks (e.g. btrfs_may_delete()), but > > > > that is the way it has always been for overlayfs. > > > > > > That's fine, underlying filesystem is just a backing store. > > > > > > > Immutability of underlying files was not my concern. > > My concern was that vfs does not provide full protection and that some > > protection is provided in fs level, because I saw IS_APPEND/IS_IMMUTABLE > > sprinkled all over the place in fs (e.g. ext4_setattr()), but I guess those are > > just leftovers and I was over concerned. > > Would be a nice cleanup to get rid of these. It would also prove > that the vfs protection is sufficient. > > > > > > > As can be seen in the comment above ovl_check_origin_xflags(), the > > > > "xflags merge" feature is designed to solve other non-standard behavior > > > > issues related to immutable directories and hardlinks in the future, but > > > > this commit does not bother to fix those cases because those are corner > > > > cases that are probably not so important to fix. > > > > > > > > A word about the design decision to merge the origin and upper xflags - > > > > Because we do not copy up fileattr and because fileattr_set breaks the > > > > link to origin xflags, the only cases where origin and upper inodes both > > > > have xflags is if upper inode was modified not via overlayfs or if the > > > > system crashed during ovl_fileattr_set() before removing the > > > > overlay.xflags xattr. In both cases, modifiying the upper inode is not > > > > going to be permitted, so it is better to reflect this in the overlay > > > > inode flags. > > > > > > So why not implement the non-merge (#3) behavior unconditionally? > > > That would solve all issues related to fileattr, right? > > > > > > > I suppose so. Note that #3 fileattr_get is still a merge between upper fileattr > > and the 4 overlay stored flags, but for inode flags it will not be a merge. > > > > I can give this a shot. > > > > While you are here, do you think that will be sufficient for the on-disk format > > of overlay.xflags? > > > > struct ovl_xflags { > > __le32 xflags; > > __le32 xflags_mask; > > } > > I think I'd prefer a slightly more complex, but user friendlier > "+i,-a,..." format. > OK, but since this is not a merge, we'd only need: overlay.xflags = "ia..." Which is compatible with the format of: chattr =<xflags> <file> Thanks, Amir.