[RFC][PATCH 7/9] evm: make rootfs a special case

[Mimi Zohar <zohar@linux.vnet.ibm.com>]

Both the EVM HMAC and signature xattr formats are file system
specific and can not be copied from one filesystem to another.

EVM differentiates files without any xattrs (INTEGRITY_UNKNOWN)
from those having protected xattrs (INTEGRITY_NOLABEL).  This
patch treats the rootfs filesystem as a special case, returning
INTEGRITY_UNKNOWN.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
---
 security/integrity/evm/evm_main.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index b392fe6..9c71af7 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -128,11 +128,16 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 	if (rc <= 0) {
 		evm_status = INTEGRITY_FAIL;
 		if (rc == -ENODATA) {
+			struct super_block *sb = dentry->d_inode->i_sb;
+
 			rc = evm_find_protected_xattrs(dentry);
-			if (rc > 0)
-				evm_status = INTEGRITY_NOLABEL;
-			else if (rc == 0)
+			if (rc == 0)
 				evm_status = INTEGRITY_NOXATTRS; /* new file */
+			else if (rc > 0 && sb->s_magic == TMPFS_MAGIC
+				 && strcmp(sb->s_id, "rootfs") == 0)
+				evm_status = INTEGRITY_UNKNOWN;
+			else if (rc > 0)
+				evm_status = INTEGRITY_NOLABEL;
 		} else if (rc == -EOPNOTSUPP) {
 			evm_status = INTEGRITY_UNKNOWN;
 		}
-- 
1.8.1.4