On Fri, May 19, 2023 at 03:42:38PM -0400, Mimi Zohar wrote: > On Fri, 2023-04-07 at 10:31 +0200, Christian Brauner wrote: > > So, I think we want both; we want the ovl_copyattr() and the > > vfs_getattr_nosec() change: > > > > (1) overlayfs should copy up the inode version in ovl_copyattr(). That > > is in line what we do with all other inode attributes. IOW, the > > overlayfs inode's i_version counter should aim to mirror the > > relevant layer's i_version counter. I wouldn't know why that > > shouldn't be the case. Asking the other way around there doesn't > > seem to be any use for overlayfs inodes to have an i_version that > > isn't just mirroring the relevant layer's i_version. > > (2) Jeff's changes for ima to make it rely on vfs_getattr_nosec(). > > Currently, ima assumes that it will get the correct i_version from > > an inode but that just doesn't hold for stacking filesystem. > > > > While (1) would likely just fix the immediate bug (2) is correct and > > _robust_. If we change how attributes are handled vfs_*() helpers will > > get updated and ima with it. Poking at raw inodes without using > > appropriate helpers is much more likely to get ima into trouble. > > In addition to properly setting the i_version for IMA, EVM has a > similar issue with i_generation and s_uuid. Adding them to > ovl_copyattr() seems to resolve it. Does that make sense? > > diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c > index 923d66d131c1..cd0aeb828868 100644 > --- a/fs/overlayfs/util.c > +++ b/fs/overlayfs/util.c > @@ -1118,5 +1118,8 @@ void ovl_copyattr(struct inode *inode) > inode->i_atime = realinode->i_atime; > inode->i_mtime = realinode->i_mtime; > inode->i_ctime = realinode->i_ctime; > + inode->i_generation = realinode->i_generation; > + if (inode->i_sb) > + uuid_copy(&inode->i_sb->s_uuid, &realinode->i_sb- Overlayfs can consist of multiple lower layers and each of those lower layers may have a different uuid. So everytime you trigger a ovl_copyattr() on a different layer this patch would alter the uuid of the overlayfs superblock. In addition the uuid should be set when the filesystem is mounted. Unless the filesystem implements a dedicated ioctl() - like ext4 - to change the uuid.
