Messages in this thread | | | Date | Wed, 31 Jan 2024 09:52:44 -0500 | Subject | Re: [PATCH 0/5] evm: Support signatures on stacked filesystem | From | Stefan Berger <> |
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On 1/31/24 08:18, Amir Goldstein wrote: > On Tue, Jan 30, 2024 at 11:46 PM Stefan Berger <stefanb@linux.ibm.com> wrote: >> >> EVM has recently been completely disabled on unsupported (e.g., >> overlayfs). This series now enables copy-up of "portable and immutable" >> signatures on those filesystems and enables the enforcement of >> "portable and immutable" as well as the "original" signatures on >> previously unsupported filesystem when EVM is enabled with EVM_INIT_X509. >> HMAC verification and generation remains disabled on those filesystems. >> > > I am missing a high level description of what is in those "portable > and immutable" > signatures and how those signatures remain valid across copy up. >
From 2/5: "Portable and immutable EVM signatures can be copied up by stacked file- system since the metadata their signature covers does not include file- system-specific data such as a file's inode number, generation, and UUID."
Instead, the signatures cover file metadata such as file mode bits, uid, and gid as well as xattrs, which can all be preserved unchanged across a copy-up.
Reference: https://elixir.bootlin.com/linux/v6.7.2/source/security/integrity/evm/evm_crypto.c#L169
> Thanks, > Amir. >
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