On Sat, 2023-05-20 at 12:15 +0300, Amir Goldstein wrote: > On Fri, May 19, 2023 at 10:42 PM Mimi Zohar <zohar@xxxxxxxxxxxxx> 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- > > >s_uuid); > > That is not a possible solution Mimi. > > The i_gneration copy *may* be acceptable in "all layers on same fs" > setup, but changing overlayfs s_uuid over and over is a non-starter. > > If you explain the problem, I may be able to help you find a better solution. EVM calculates an HMAC of the file metadata (security xattrs, i_ino, i_generation, i_uid, i_gid, i_mode, s_uuid) and stores it as security.evm. Notrmally this would be used for mutable files, which cannot be signed. The i_generation and s_uuid on the lower layer and the overlay are not the same, causing the EVM HMAC verification to fail. -- thanks, Mimi
