The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 9eea2904292c2d8fa98df141d3bf7c41ec9dc1b5 Mon Sep 17 00:00:00 2001
From: Roberto Sassu roberto.sassu@huawei.com Date: Fri, 14 May 2021 17:27:42 +0200 Subject: [PATCH] evm: Execute evm_inode_init_security() only when an HMAC key is loaded
evm_inode_init_security() requires an HMAC key to calculate the HMAC on initial xattrs provided by LSMs. However, it checks generically whether a key has been loaded, including also public keys, which is not correct as public keys are not suitable to calculate the HMAC.
Originally, support for signature verification was introduced to verify a possibly immutable initial ram disk, when no new files are created, and to switch to HMAC for the root filesystem. By that time, an HMAC key should have been loaded and usable to calculate HMACs for new files.
More recently support for requiring an HMAC key was removed from the kernel, so that signature verification can be used alone. Since this is a legitimate use case, evm_inode_init_security() should not return an error when no HMAC key has been loaded.
This patch fixes this problem by replacing the evm_key_loaded() check with a check of the EVM_INIT_HMAC flag in evm_initialized.
Fixes: 26ddabfe96b ("evm: enable EVM when X509 certificate is loaded") Signed-off-by: Roberto Sassu roberto.sassu@huawei.com Cc: stable@vger.kernel.org # 4.5.x Signed-off-by: Mimi Zohar zohar@linux.ibm.com
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c index 0de367aaa2d3..7ac5204c8d1f 100644 --- a/security/integrity/evm/evm_main.c +++ b/security/integrity/evm/evm_main.c @@ -521,7 +521,7 @@ void evm_inode_post_setattr(struct dentry *dentry, int ia_valid) }
/* - * evm_inode_init_security - initializes security.evm + * evm_inode_init_security - initializes security.evm HMAC value */ int evm_inode_init_security(struct inode *inode, const struct xattr *lsm_xattr, @@ -530,7 +530,8 @@ int evm_inode_init_security(struct inode *inode, struct evm_xattr *xattr_data; int rc;
- if (!evm_key_loaded() || !evm_protected_xattr(lsm_xattr->name)) + if (!(evm_initialized & EVM_INIT_HMAC) || + !evm_protected_xattr(lsm_xattr->name)) return 0;
xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);