evm: labeling pseudo filesystems exception

[ Upstream commit 5101a185 ]

To prevent offline stripping of existing file xattrs and relabeling of
them at runtime, EVM allows only newly created files to be labeled.  As
pseudo filesystems are not persistent, stripping of xattrs is not a
concern.

Some LSMs defer file labeling on pseudo filesystems.  This patch
permits the labeling of existing files on pseudo files systems.
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

security/integrity/evm/evm_main.c

@@ -22,6 +22,7 @@
 #include <linux/xattr.h>
 #include <linux/integrity.h>
 #include <linux/evm.h>
+#include <linux/magic.h>
 #include <crypto/hash.h>
 #include "evm.h"
 
@@ -291,6 +292,17 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
 		iint = integrity_iint_find(dentry->d_inode);
 		if (iint && (iint->flags & IMA_NEW_FILE))
 			return 0;
+
+		/* exception for pseudo filesystems */
+		if (dentry->d_inode->i_sb->s_magic == TMPFS_MAGIC
+		    || dentry->d_inode->i_sb->s_magic == SYSFS_MAGIC)
+			return 0;
+
+		integrity_audit_msg(AUDIT_INTEGRITY_METADATA,
+				    dentry->d_inode, dentry->d_name.name,
+				    "update_metadata",
+				    integrity_status_msg[evm_status],
+				    -EPERM, 0);
 	}
 out:
 	if (evm_status != INTEGRITY_PASS)