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evm: Enforce signatures on unsupported filesystem for EVM_INIT_X509

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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>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
This commit is contained in:
Stefan Berger 2024-02-23 12:25:11 -05:00 committed by Mimi Zohar
parent cd9b909a11
commit 47add87ad1
1 changed files with 7 additions and 5 deletions
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12
security/integrity/evm/evm_main.c
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@ -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);
}