ima: Allow choice of file hash algorithm for measurement and audit

hulk inclusion
category: feature
feature: IMA Digest Lists extension
bugzilla: 46797

-------------------------------------------------

IMA reads the hash algorithm from security.ima, if exists, so that a
signature can be verified with the correct file digest.

This patch moves ima_read_xattr() and ima_get_hash_algo() to ima_main.c, so
that the file digest in the measurement list or in the audit logs can be
compared with a reference value calculated with a specific hash algorithm.

In addition, this patch also allows the usage of security.ima with type
EVM_IMA_XATTR_DIGSIG and signature length zero, so that the xattr can be
used just to specify the hash algorithm.
Signed-off-by: NRoberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: NTianxing Zhang <zhangtianxing3@huawei.com>
Reviewed-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

security/integrity/ima/ima.h

@@ -316,11 +316,6 @@ int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func);
 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file);
 enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
 					   enum ima_hooks func);
-enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
-				 int xattr_len);
-int ima_read_xattr(struct dentry *dentry,
-		   struct evm_ima_xattr_data **xattr_value);
-
 #else
 static inline int ima_check_blacklist(struct integrity_iint_cache *iint,
 				      const struct modsig *modsig, int pcr)
@@ -357,18 +352,6 @@ static inline enum integrity_status ima_get_cache_status(struct integrity_iint_c
 	return INTEGRITY_UNKNOWN;
 }
 
-static inline enum hash_algo
-ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value, int xattr_len)
-{
-	return ima_hash_algo;
-}
-
-static inline int ima_read_xattr(struct dentry *dentry,
-				 struct evm_ima_xattr_data **xattr_value)
-{
-	return 0;
-}
-
 #endif /* CONFIG_IMA_APPRAISE */
 
 #ifdef CONFIG_IMA_APPRAISE_MODSIG

security/integrity/ima/ima_appraise.c

@@ -169,58 +169,6 @@ static void ima_cache_flags(struct integrity_iint_cache *iint,
 	}
 }
 
-enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
-				 int xattr_len)
-{
-	struct signature_v2_hdr *sig;
-	enum hash_algo ret;
-
-	if (!xattr_value || xattr_len < 2)
-		/* return default hash algo */
-		return ima_hash_algo;
-
-	switch (xattr_value->type) {
-	case EVM_IMA_XATTR_DIGSIG:
-		sig = (typeof(sig))xattr_value;
-		if (sig->version != 2 || xattr_len <= sizeof(*sig))
-			return ima_hash_algo;
-		return sig->hash_algo;
-		break;
-	case IMA_XATTR_DIGEST_NG:
-		/* first byte contains algorithm id */
-		ret = xattr_value->data[0];
-		if (ret < HASH_ALGO__LAST)
-			return ret;
-		break;
-	case IMA_XATTR_DIGEST:
-		/* this is for backward compatibility */
-		if (xattr_len == 21) {
-			unsigned int zero = 0;
-			if (!memcmp(&xattr_value->data[16], &zero, 4))
-				return HASH_ALGO_MD5;
-			else
-				return HASH_ALGO_SHA1;
-		} else if (xattr_len == 17)
-			return HASH_ALGO_MD5;
-		break;
-	}
-
-	/* return default hash algo */
-	return ima_hash_algo;
-}
-
-int ima_read_xattr(struct dentry *dentry,
-		   struct evm_ima_xattr_data **xattr_value)
-{
-	ssize_t ret;
-
-	ret = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
-				 0, GFP_NOFS);
-	if (ret == -EOPNOTSUPP)
-		ret = 0;
-	return ret;
-}
-
 /*
  * xattr_verify - verify xattr digest or signature
  *
@@ -387,6 +335,10 @@ int ima_appraise_measurement(enum ima_hooks func,
 	if (!(inode->i_opflags & IOP_XATTR) && !try_modsig)
 		return INTEGRITY_UNKNOWN;
 
+	if (xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG &&
+	    xattr_len == sizeof(struct signature_v2_hdr))
+		rc = -ENODATA;
+
 	/* If reading the xattr failed and there's no modsig, error out. */
 	if (rc <= 0 && !try_modsig) {
 		if (rc && rc != -ENODATA)

security/integrity/ima/ima_main.c

@@ -147,6 +147,58 @@ static void ima_rdwr_violation_check(struct file *file,
 				  "invalid_pcr", "open_writers");
 }
 
+static enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
+					int xattr_len)
+{
+	struct signature_v2_hdr *sig;
+	enum hash_algo ret;
+
+	if (!xattr_value || xattr_len < 2)
+		/* return default hash algo */
+		return ima_hash_algo;
+
+	switch (xattr_value->type) {
+	case EVM_IMA_XATTR_DIGSIG:
+		sig = (typeof(sig))xattr_value;
+		if (sig->version != 2 || xattr_len < sizeof(*sig))
+			return ima_hash_algo;
+		return sig->hash_algo;
+		break;
+	case IMA_XATTR_DIGEST_NG:
+		/* first byte contains algorithm id */
+		ret = xattr_value->data[0];
+		if (ret < HASH_ALGO__LAST)
+			return ret;
+		break;
+	case IMA_XATTR_DIGEST:
+		/* this is for backward compatibility */
+		if (xattr_len == 21) {
+			unsigned int zero = 0;
+			if (!memcmp(&xattr_value->data[16], &zero, 4))
+				return HASH_ALGO_MD5;
+			else
+				return HASH_ALGO_SHA1;
+		} else if (xattr_len == 17)
+			return HASH_ALGO_MD5;
+		break;
+	}
+
+	/* return default hash algo */
+	return ima_hash_algo;
+}
+
+static int ima_read_xattr(struct dentry *dentry,
+			  struct evm_ima_xattr_data **xattr_value)
+{
+	ssize_t ret;
+
+	ret = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)xattr_value,
+				 0, GFP_NOFS);
+	if (ret == -EOPNOTSUPP)
+		ret = 0;
+	return ret;
+}
+
 static void ima_check_last_writer(struct integrity_iint_cache *iint,
 				  struct inode *inode, struct file *file)
 {