[PATCH 5/5] evm: Support multiple LSMs providing an xattr

[Roberto Sassu]

Currently, evm_inode_init_security() takes as input a single LSM xattr,
passed by security_inode_init_security(), and calculates the HMAC on it and
other inode metadata.

Given that initxattrs(), called by security_inode_init_security(), expects
that this array is terminated when the xattr name is set to NULL, this
patch reuses the same assumption for evm_inode_init_security() to scan all
xattrs and to calculate the HMAC on all of them.

Signed-off-by: Roberto Sassu <roberto.sa...@huawei.com>
---
 security/integrity/evm/evm.h        |  2 ++
 security/integrity/evm/evm_crypto.c |  9 ++++++++-
 security/integrity/evm/evm_main.c   | 15 +++++++++++----
 3 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/security/integrity/evm/evm.h b/security/integrity/evm/evm.h
index ae590f71ce7d..24eac42b9f32 100644
--- a/security/integrity/evm/evm.h
+++ b/security/integrity/evm/evm.h
@@ -49,6 +49,8 @@ struct evm_digest {
        char digest[IMA_MAX_DIGEST_SIZE];
 } __packed;
 
+int evm_protected_xattr(const char *req_xattr_name);
+
 int evm_init_key(void);
 int __init evm_init_crypto(void);
 int evm_update_evmxattr(struct dentry *dentry,
diff --git a/security/integrity/evm/evm_crypto.c 
b/security/integrity/evm/evm_crypto.c
index b66264b53d5d..35c5eec0517d 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -358,6 +358,7 @@ int evm_init_hmac(struct inode *inode, const struct xattr 
*lsm_xattr,
                  char *hmac_val)
 {
        struct shash_desc *desc;
+       const struct xattr *xattr;
 
        desc = init_desc(EVM_XATTR_HMAC, evm_hash_algo);
        if (IS_ERR(desc)) {
@@ -365,7 +366,13 @@ int evm_init_hmac(struct inode *inode, const struct xattr 
*lsm_xattr,
                return PTR_ERR(desc);
        }
 
-       crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
+       for (xattr = lsm_xattr; xattr->name != NULL; xattr++) {
+               if (!evm_protected_xattr(xattr->name))
+                       continue;
+
+               crypto_shash_update(desc, xattr->value, xattr->value_len);
+       }
+
        hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
        kfree(desc);
        return 0;
diff --git a/security/integrity/evm/evm_main.c 
b/security/integrity/evm/evm_main.c
index a5069d69a893..fde366149499 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -260,7 +260,7 @@ static enum integrity_status evm_verify_hmac(struct dentry 
*dentry,
        return evm_status;
 }
 
-static int evm_protected_xattr(const char *req_xattr_name)
+int evm_protected_xattr(const char *req_xattr_name)
 {
        int namelen;
        int found = 0;
@@ -712,14 +712,21 @@ int evm_inode_init_security(struct inode *inode, struct 
inode *dir,
                            void **value, size_t *len,
                            struct xattr *lsm_xattrs)
 {
+       struct xattr *xattr;
        struct evm_xattr *xattr_data;
-       int rc;
+       int rc, evm_protected_xattrs = 0;
 
        if (!name || !value || !len || !lsm_xattrs)
                return 0;
 
-       if (!(evm_initialized & EVM_INIT_HMAC) ||
-           !evm_protected_xattr(lsm_xattrs->name))
+       if (!(evm_initialized & EVM_INIT_HMAC))
+               return -EOPNOTSUPP;
+
+       for (xattr = lsm_xattrs; xattr && xattr->name != NULL; xattr++)
+               if (evm_protected_xattr(xattr->name))
+                       evm_protected_xattrs++;
+
+       if (!evm_protected_xattrs)
                return -EOPNOTSUPP;
 
        xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
-- 
2.26.2