linux-kernel - [PATCH AUTOSEL 6.4 45/54] ovl: Always reevaluate the file signature for IMA

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Date:   Sun, 13 Aug 2023 11:49:24 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Eric Snowberg <eric.snowberg@...cle.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>, miklos@...redi.hu,
        amir73il@...il.com, linux-unionfs@...r.kernel.org
Subject: [PATCH AUTOSEL 6.4 45/54] ovl: Always reevaluate the file signature for IMA

From: Eric Snowberg <eric.snowberg@...cle.com>

[ Upstream commit 18b44bc5a67275641fb26f2c54ba7eef80ac5950 ]

Commit db1d1e8b9867 ("IMA: use vfs_getattr_nosec to get the i_version")
partially closed an IMA integrity issue when directly modifying a file
on the lower filesystem.  If the overlay file is first opened by a user
and later the lower backing file is modified by root, but the extended
attribute is NOT updated, the signature validation succeeds with the old
original signature.

Update the super_block s_iflags to SB_I_IMA_UNVERIFIABLE_SIGNATURE to
force signature reevaluation on every file access until a fine grained
solution can be found.

Signed-off-by: Eric Snowberg <eric.snowberg@...cle.com>
Signed-off-by: Mimi Zohar <zohar@...ux.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/overlayfs/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index ae1058fbfb5b2..8c60da7b4afd8 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -2052,7 +2052,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 		ovl_trusted_xattr_handlers;
 	sb->s_fs_info = ofs;
 	sb->s_flags |= SB_POSIXACL;
-	sb->s_iflags |= SB_I_SKIP_SYNC;
+	sb->s_iflags |= SB_I_SKIP_SYNC | SB_I_IMA_UNVERIFIABLE_SIGNATURE;
 
 	err = -ENOMEM;
 	root_dentry = ovl_get_root(sb, upperpath.dentry, oe);
-- 
2.40.1