Commit 47add87a authored by Stefan Berger's avatar Stefan Berger Committed by Mimi Zohar
Browse files

evm: Enforce signatures on unsupported filesystem for EVM_INIT_X509 



Unsupported filesystems currently do not enforce any signatures. Add
support for signature enforcement of the "original" and "portable &
immutable" signatures when EVM_INIT_X509 is enabled.

The "original" signature type contains filesystem specific metadata.
Thus it cannot be copied up and verified. However with EVM_INIT_X509
and EVM_ALLOW_METADATA_WRITES enabled, the "original" file signature
may be written.

When EVM_ALLOW_METADATA_WRITES is not set or once it is removed from
/sys/kernel/security/evm by setting EVM_INIT_HMAC for example, it is not
possible to write or remove xattrs on the overlay filesystem.

This change still prevents EVM from writing HMAC signatures on
unsupported filesystem when EVM_INIT_HMAC is enabled.

Co-developed-by: default avatarMimi Zohar <zohar@linux.ibm.com>
Signed-off-by: default avatarStefan Berger <stefanb@linux.ibm.com>
Signed-off-by: default avatarMimi Zohar <zohar@linux.ibm.com>
parent cd9b909a

security/integrity/evm/evm_main.c

+7 −5
Original line number Diff line number Diff line
@@ -192,7 +192,11 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry, 
		     iint->evm_status == INTEGRITY_PASS_IMMUTABLE))

		return iint->evm_status;



	if (is_unsupported_fs(dentry))

	/*

	 * On unsupported filesystems without EVM_INIT_X509 enabled, skip

	 * signature verification.

	 */

	if (!(evm_initialized & EVM_INIT_X509) && is_unsupported_fs(dentry))

		return INTEGRITY_UNKNOWN;



	/* if status is not PASS, try to check again - against -ENOMEM */
@@ -261,7 +265,8 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry, 
				evm_status = INTEGRITY_PASS_IMMUTABLE;

			} else if (!IS_RDONLY(inode) &&

				   !(inode->i_sb->s_readonly_remount) &&

				   !IS_IMMUTABLE(inode)) {

				   !IS_IMMUTABLE(inode) &&

				   !is_unsupported_fs(dentry)) {

				evm_update_evmxattr(dentry, xattr_name,

						    xattr_value,

						    xattr_value_len);
@@ -419,9 +424,6 @@ enum integrity_status evm_verifyxattr(struct dentry *dentry, 
	if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))

		return INTEGRITY_UNKNOWN;



	if (is_unsupported_fs(dentry))

		return INTEGRITY_UNKNOWN;



	return evm_verify_hmac(dentry, xattr_name, xattr_value,

				 xattr_value_len);

}