ovl: Always reevaluate the file signature for IMA

[ 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@oracle.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 51eec4a..08d3a1f 100644 (file)
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -2155,7 +2155,7 @@ 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);