diff mbox series

[v3,08/10] evm: Enforce signatures on unsupported filesystem for EVM_INIT_X509

Message ID 20240223172513.4049959-9-stefanb@linux.ibm.com (mailing list archive)
State Handled Elsewhere
Delegated to: Paul Moore
Headers show
Series evm: Support signatures on stacked filesystem | expand

Commit Message

Stefan Berger Feb. 23, 2024, 5:25 p.m. UTC
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: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
 security/integrity/evm/evm_main.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

Comments

Mimi Zohar March 19, 2024, 11:26 p.m. UTC | #1
On Fri, 2024-02-23 at 12:25 -0500, Stefan Berger wrote:
> 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 paragraph is currently correct, but at some point EVM_ALLOW_METADATA_WRITES
will be deprecated.  Refer to commit 1434c6a1d32a ("evm: Deprecate
EVM_ALLOW_METADATA_WRITES").

Mimi

> 
> This change still prevents EVM from writing HMAC signatures on
> unsupported filesystem when EVM_INIT_HMAC is enabled.
> 
> Co-developed-by: Mimi Zohar <zohar@linux.ibm.com>
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>

Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
diff mbox series

Patch

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index c1ca0894cd8a..cfb4f9809369 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -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);
 }