On Tue, 2024-04-23 at 13:06 +0200, Miklos Szeredi wrote: > On Tue, 16 Apr 2024 at 21:06, Mimi Zohar <[email protected]> wrote: > > On Tue, 2024-04-16 at 16:46 +0200, Miklos Szeredi wrote: > > > On Tue, 16 Apr 2024 at 14:18, Mimi Zohar <[email protected]> wrote: > > > > Originally there was a single measureent unless the filesystem was > > > > mounted with > > > > SB_I_VERSION. With commit a2a2c3c8580a ("ima: Use i_version only when > > > > filesystem supports it") this changed to always re-measure the file if > > > > the > > > > filesystem wasn't mounted with SB_I_VERSION. > > > > > > Does the i_version get stored and compared only while the inode is in > > > memory? > > > > > > In that case I think it should be possible to support a version number > > > for the overlay inode. > > > > i_version was insufficient to detect a file change for overlay. Commit > > b836c4d29f27 ("ima: detect changes to the backing overlay") also compares > > the > > i_ino and s_dev as well. Refer to > > https://lore.kernel.org/lkml/[email protected]/. > > Which is rather ad-hoc. > > I'm talking about returning something in overlay i_version, which > really indicates the version of the overlay file calculated from the > i_version of the underlying files. The only issue is making this > i_version persistent, AFAICS. If that's not needed than the overlayfs > specific logic in IMA could be moved into overlayfs, where it belongs.
IMA saves the i_version in order to detect whether or not the file has changed. between one access and another. The i_version value, itself, does not need to be persistent but needs to be consistent. > > > Here in this patch set we need to detect IMA read/write violations, based > > on the > > i_readcount/i_writecount. If an overlay file is opened for read, but the > > backing file is already opened for write, the file measurement is > > meaningless. An "open-writers" violation needs to be generated; and the IMA > > measurement list needs to be invalidated. > > If there's no other way, then let's implement an API to query the > writecount that can take overlayfs into account. This is for the VFS > and/or overlayfs to calculate, not for IMA. Thanks, that will definitely simplify IMA. Mimi
