[PATCH AUTOSEL 5.10 20/25] ovl: Always reevaluate the file signature for IMA

[Sasha Levin]

From: Eric Snowberg <eric.snowberg@xxxxxxxxxx>

[ 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@xxxxxxxxxx>
Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 5d7df839902df..e0384095ca960 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -2028,7 +2028,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	sb->s_xattr = ovl_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