linux-kernel - Re: [PATCH] overlayfs: Trigger file re-evaluation by IMA / EVM after writes

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Message-ID: <078d8c1fd6b6de59cde8aa85f8e59a056cb78614.camel@linux.ibm.com>
Date:   Fri, 19 May 2023 15:42:38 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Christian Brauner <brauner@...nel.org>,
        Amir Goldstein <amir73il@...il.com>,
        Jeff Layton <jlayton@...nel.org>
Cc:     Stefan Berger <stefanb@...ux.ibm.com>,
        Paul Moore <paul@...l-moore.com>,
        linux-integrity@...r.kernel.org, miklos@...redi.hu,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-unionfs@...r.kernel.org,
        Ignaz Forster <iforster@...e.de>, Petr Vorel <pvorel@...e.cz>
Subject: Re: [PATCH] overlayfs: Trigger file re-evaluation by IMA / EVM
 after writes

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);
 	i_size_write(inode, i_size_read(realinode));
 }
-- 
thanks,

Mimib