ima: add ima_inode_setxattr/removexattr function and calls

Based on xattr_permission comments, the restriction to modify 'security'
xattr is left up to the underlying fs or lsm. Ensure that not just anyone
can modify or remove 'security.ima'.

Changelog v1:
- Unless IMA-APPRAISE is configured, use stub ima_inode_removexattr()/setxattr()
  functions.  (Moved ima_inode_removexattr()/setxattr() to ima_appraise.c)

Changelog:
  - take i_mutex to fix locking (Dmitry Kasatkin)
  - ima_reset_appraise_flags should only be called when modifying or
    removing the 'security.ima' xattr. Requires CAP_SYS_ADMIN privilege.
    (Incorporated fix from Roberto Sassu)
  - Even if allowed to update security.ima, reset the appraisal flags,
    forcing re-appraisal.
  - Replace CAP_MAC_ADMIN with CAP_SYS_ADMIN
  - static inline ima_inode_setxattr()/ima_inode_removexattr() stubs
  - ima_protect_xattr should be static

Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>

security/security.c

@@ -571,6 +571,9 @@ int security_inode_setxattr(struct dentry *dentry, const char *name,
 	if (unlikely(IS_PRIVATE(dentry->d_inode)))
 		return 0;
 	ret = security_ops->inode_setxattr(dentry, name, value, size, flags);
+	if (ret)
+		return ret;
+	ret = ima_inode_setxattr(dentry, name, value, size);
 	if (ret)
 		return ret;
 	return evm_inode_setxattr(dentry, name, value, size);
@@ -606,6 +609,9 @@ int security_inode_removexattr(struct dentry *dentry, const char *name)
 	if (unlikely(IS_PRIVATE(dentry->d_inode)))
 		return 0;
 	ret = security_ops->inode_removexattr(dentry, name);
+	if (ret)
+		return ret;
+	ret = ima_inode_removexattr(dentry, name);
 	if (ret)
 		return ret;
 	return evm_inode_removexattr(dentry, name);