[PATCH v8 5/6] evm: Align evm_inode_init_security() definition with LSM infrastructure

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>

Change the evm_inode_init_security() definition to align with the LSM
infrastructure. Keep the existing behavior of including in the HMAC
calculation only the first xattr provided by LSMs.

Changing the evm_inode_init_security() definition requires passing only the
xattr array allocated by security_inode_init_security(), instead of the
first LSM xattr and the place where the EVM xattr should be filled. In lieu
of passing the EVM xattr, EVM must position itself after the last filled
xattr (by checking the xattr name), since only the beginning of the xattr
array is given.

Finally, make evm_inode_init_security() return value compatible with the
inode_init_security hook conventions, i.e. return -EOPNOTSUPP if it is not
setting an xattr.

EVM is a bit tricky, because xattrs is both an input and an output. If it
was just output, EVM should have returned zero if xattrs is NULL. But,
since xattrs is also input, EVM is unable to do its calculations, so return
-EOPNOTSUPP and handle this error in security_inode_init_security().

Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
Reviewed-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
---
 include/linux/evm.h               | 12 ++++++------
 security/integrity/evm/evm_main.c | 25 ++++++++++++++++++-------
 security/security.c               |  5 ++---
 3 files changed, 26 insertions(+), 16 deletions(-)

diff --git a/include/linux/evm.h b/include/linux/evm.h
index 7dc1ee74169..cc64cea354e 100644
--- a/include/linux/evm.h
+++ b/include/linux/evm.h
@@ -56,9 +56,9 @@ static inline void evm_inode_post_set_acl(struct dentry *dentry,
 {
 	return evm_inode_post_setxattr(dentry, acl_name, NULL, 0);
 }
-extern int evm_inode_init_security(struct inode *inode,
-				   const struct xattr *xattr_array,
-				   struct xattr *evm);
+extern int evm_inode_init_security(struct inode *inode, struct inode *dir,
+				   const struct qstr *qstr,
+				   struct xattr *xattrs);
 extern bool evm_revalidate_status(const char *xattr_name);
 extern int evm_protected_xattr_if_enabled(const char *req_xattr_name);
 extern int evm_read_protected_xattrs(struct dentry *dentry, u8 *buffer,
@@ -157,9 +157,9 @@ static inline void evm_inode_post_set_acl(struct dentry *dentry,
 	return;
 }
 
-static inline int evm_inode_init_security(struct inode *inode,
-					  const struct xattr *xattr_array,
-					  struct xattr *evm)
+static inline int evm_inode_init_security(struct inode *inode, struct inode *dir,
+					  const struct qstr *qstr,
+					  struct xattr *xattrs)
 {
 	return 0;
 }
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index cf24c525558..7d20ce83915 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -864,23 +864,34 @@ void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
 /*
  * evm_inode_init_security - initializes security.evm HMAC value
  */
-int evm_inode_init_security(struct inode *inode,
-				 const struct xattr *lsm_xattr,
-				 struct xattr *evm_xattr)
+int evm_inode_init_security(struct inode *inode, struct inode *dir,
+			    const struct qstr *qstr,
+			    struct xattr *xattrs)
 {
 	struct evm_xattr *xattr_data;
+	struct xattr *xattr, *evm_xattr;
 	int rc;
 
-	if (!(evm_initialized & EVM_INIT_HMAC) ||
-	    !evm_protected_xattr(lsm_xattr->name))
-		return 0;
+	if (!(evm_initialized & EVM_INIT_HMAC) || !xattrs ||
+	    !evm_protected_xattr(xattrs->name))
+		return -EOPNOTSUPP;
+
+	/*
+	 * security_inode_init_security() makes sure that the xattrs array is
+	 * contiguous, there is enough space for security.evm, and that there is
+	 * a terminator at the end of the array.
+	 */
+	for (xattr = xattrs; xattr->name != NULL; xattr++)
+		;
+
+	evm_xattr = xattr;
 
 	xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
 	if (!xattr_data)
 		return -ENOMEM;
 
 	xattr_data->data.type = EVM_XATTR_HMAC;
-	rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
+	rc = evm_init_hmac(inode, xattrs, xattr_data->digest);
 	if (rc < 0)
 		goto out;
 
diff --git a/security/security.c b/security/security.c
index f1f5f62f7fa..d0e20b26b6c 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1705,9 +1705,8 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 	if (!num_filled_xattrs)
 		goto out;
 
-	ret = evm_inode_init_security(inode, new_xattrs,
-				      new_xattrs + num_filled_xattrs);
-	if (ret)
+	ret = evm_inode_init_security(inode, dir, qstr, new_xattrs);
+	if (ret && ret != -EOPNOTSUPP)
 		goto out;
 	ret = initxattrs(inode, new_xattrs, fs_data);
 out:
-- 
2.25.1