diff mbox

[V4] evm: Allow non-SHA1 digital signatures

Message ID 20180517220938.102953-1-mjg59@google.com (mailing list archive)
State New, archived
Headers show

Commit Message

Matthew Garrett May 17, 2018, 10:09 p.m. UTC 
Oh bother - I think I see what's wrong. Does this version work better?
I'm afraid I only tested against signatures rather than HMACs, and I was
generating a raw SHA1 rather than an HMAC :(

Comments

Mimi Zohar May 18, 2018, 4:03 p.m. UTC | #1 
On Thu, 2018-05-17 at 15:09 -0700, Matthew Garrett wrote:
> Oh bother - I think I see what's wrong. Does this version work better?
> I'm afraid I only tested against signatures rather than HMACs, and I was
> generating a raw SHA1 rather than an HMAC :(

That's a lot better!

FYI, Wang Junwen reported a problem with enabling EVM with just the
immutable and portable keys.  Without trusted keys enabled, SHA1 isn't
being built into the kernel.  Loading the SHA1 kernel module fails.
 Without knowing apriori which hash algorithms need to be builtin is a
problem.

Mimi

> 
> diff --git a/security/integrity/evm/evm.h b/security/integrity/evm/evm.h
> index 45c4a89c02ff..a8289fbf2f0c 100644
> --- a/security/integrity/evm/evm.h
> +++ b/security/integrity/evm/evm.h
> @@ -42,6 +42,11 @@ extern struct crypto_shash *hash_tfm;
>  /* List of EVM protected security xattrs */
>  extern char *evm_config_xattrnames[];
> 
> +struct evm_digest {
> +	struct ima_digest_data hdr;
> +	char digest[IMA_MAX_DIGEST_SIZE];
> +} __packed;
> +
>  int evm_init_key(void);
>  int evm_update_evmxattr(struct dentry *dentry,
>  			const char *req_xattr_name,
> @@ -49,10 +54,11 @@ int evm_update_evmxattr(struct dentry *dentry,
>  			size_t req_xattr_value_len);
>  int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
>  		  const char *req_xattr_value,
> -		  size_t req_xattr_value_len, char *digest);
> +		  size_t req_xattr_value_len, struct evm_digest *data);
>  int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
>  		  const char *req_xattr_value,
> -		  size_t req_xattr_value_len, char type, char *digest);
> +		  size_t req_xattr_value_len, char type,
> +		  struct evm_digest *data);
>  int evm_init_hmac(struct inode *inode, const struct xattr *xattr,
>  		  char *hmac_val);
>  int evm_init_secfs(void);
> diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
> index a46fba322340..eb87d40c62a5 100644
> --- a/security/integrity/evm/evm_crypto.c
> +++ b/security/integrity/evm/evm_crypto.c
> @@ -21,6 +21,7 @@
>  #include <linux/evm.h>
>  #include <keys/encrypted-type.h>
>  #include <crypto/hash.h>
> +#include <crypto/hash_info.h>
>  #include "evm.h"
> 
>  #define EVMKEY "evm-key"
> @@ -29,7 +30,7 @@ static unsigned char evmkey[MAX_KEY_SIZE];
>  static int evmkey_len = MAX_KEY_SIZE;
> 
>  struct crypto_shash *hmac_tfm;
> -struct crypto_shash *hash_tfm;
> +static struct crypto_shash *evm_tfm[HASH_ALGO__LAST];
> 
>  static DEFINE_MUTEX(mutex);
> 
> @@ -38,7 +39,6 @@ static DEFINE_MUTEX(mutex);
>  static unsigned long evm_set_key_flags;
> 
>  static char * const evm_hmac = "hmac(sha1)";
> -static char * const evm_hash = "sha1";
> 
>  /**
>   * evm_set_key() - set EVM HMAC key from the kernel
> @@ -74,10 +74,10 @@ int evm_set_key(void *key, size_t keylen)
>  }
>  EXPORT_SYMBOL_GPL(evm_set_key);
> 
> -static struct shash_desc *init_desc(char type)
> +static struct shash_desc *init_desc(char type, uint8_t hash_algo)
>  {
>  	long rc;
> -	char *algo;
> +	const char *algo;
>  	struct crypto_shash **tfm;
>  	struct shash_desc *desc;
> 
> @@ -89,8 +89,8 @@ static struct shash_desc *init_desc(char type)
>  		tfm = &hmac_tfm;
>  		algo = evm_hmac;
>  	} else {
> -		tfm = &hash_tfm;
> -		algo = evm_hash;
> +		tfm = &evm_tfm[hash_algo];
> +		algo = hash_algo_name[hash_algo];
>  	}
> 
>  	if (*tfm == NULL) {
> @@ -186,10 +186,10 @@ static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
>   * each xattr, but attempt to re-use the previously allocated memory.
>   */
>  static int evm_calc_hmac_or_hash(struct dentry *dentry,
> -				const char *req_xattr_name,
> -				const char *req_xattr_value,
> -				size_t req_xattr_value_len,
> -				char type, char *digest)
> +				 const char *req_xattr_name,
> +				 const char *req_xattr_value,
> +				 size_t req_xattr_value_len,
> +				 uint8_t type, struct evm_digest *data)
>  {
>  	struct inode *inode = d_backing_inode(dentry);
>  	struct shash_desc *desc;
> @@ -203,10 +203,12 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry,
>  	if (!(inode->i_opflags & IOP_XATTR))
>  		return -EOPNOTSUPP;
> 
> -	desc = init_desc(type);
> +	desc = init_desc(type, data->hdr.algo);
>  	if (IS_ERR(desc))
>  		return PTR_ERR(desc);
> 
> +	data->hdr.length = crypto_shash_digestsize(desc->tfm);
> +
>  	error = -ENODATA;
>  	for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
>  		bool is_ima = false;
> @@ -238,7 +240,7 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry,
>  		if (is_ima)
>  			ima_present = true;
>  	}
> -	hmac_add_misc(desc, inode, type, digest);
> +	hmac_add_misc(desc, inode, type, data->digest);
> 
>  	/* Portable EVM signatures must include an IMA hash */
>  	if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
> @@ -251,18 +253,18 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry,
> 
>  int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
>  		  const char *req_xattr_value, size_t req_xattr_value_len,
> -		  char *digest)
> +		  struct evm_digest *data)
>  {
>  	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
> -			       req_xattr_value_len, EVM_XATTR_HMAC, digest);
> +				    req_xattr_value_len, EVM_XATTR_HMAC, data);
>  }
> 
>  int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
>  		  const char *req_xattr_value, size_t req_xattr_value_len,
> -		  char type, char *digest)
> +		  char type, struct evm_digest *data)
>  {
>  	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
> -				     req_xattr_value_len, type, digest);
> +				     req_xattr_value_len, type, data);
>  }
> 
>  static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
> @@ -302,7 +304,7 @@ int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
>  			const char *xattr_value, size_t xattr_value_len)
>  {
>  	struct inode *inode = d_backing_inode(dentry);
> -	struct evm_ima_xattr_data xattr_data;
> +	struct evm_digest data;
>  	int rc = 0;
> 
>  	/*
> @@ -315,13 +317,14 @@ int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
>  	if (rc)
>  		return -EPERM;
> 
> +	data.hdr.algo = HASH_ALGO_SHA1;
>  	rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
> -			   xattr_value_len, xattr_data.digest);
> +			   xattr_value_len, &data);
>  	if (rc == 0) {
> -		xattr_data.type = EVM_XATTR_HMAC;
> +		data.hdr.xattr.sha1.type = EVM_XATTR_HMAC;
>  		rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
> -					   &xattr_data,
> -					   sizeof(xattr_data), 0);
> +					   &data.hdr.xattr.data[1],
> +					   SHA1_DIGEST_SIZE + 1, 0);
>  	} else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
>  		rc = __vfs_removexattr(dentry, XATTR_NAME_EVM);
>  	}
> @@ -333,7 +336,7 @@ int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
>  {
>  	struct shash_desc *desc;
> 
> -	desc = init_desc(EVM_XATTR_HMAC);
> +	desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
>  	if (IS_ERR(desc)) {
>  		pr_info("init_desc failed\n");
>  		return PTR_ERR(desc);
> diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
> index 9ea9c19a545c..88ea9c1962d6 100644
> --- a/security/integrity/evm/evm_main.c
> +++ b/security/integrity/evm/evm_main.c
> @@ -25,6 +25,7 @@
>  #include <linux/magic.h>
> 
>  #include <crypto/hash.h>
> +#include <crypto/hash_info.h>
>  #include <crypto/algapi.h>
>  #include "evm.h"
> 
> @@ -122,8 +123,9 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
>  					     struct integrity_iint_cache *iint)
>  {
>  	struct evm_ima_xattr_data *xattr_data = NULL;
> -	struct evm_ima_xattr_data calc;
> +	struct signature_v2_hdr *hdr;
>  	enum integrity_status evm_status = INTEGRITY_PASS;
> +	struct evm_digest digest;
>  	struct inode *inode;
>  	int rc, xattr_len;
> 
> @@ -159,25 +161,28 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
>  			evm_status = INTEGRITY_FAIL;
>  			goto out;
>  		}
> +
> +		digest.hdr.algo = HASH_ALGO_SHA1;
>  		rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
> -				   xattr_value_len, calc.digest);
> +				   xattr_value_len, &digest);
>  		if (rc)
>  			break;
> -		rc = crypto_memneq(xattr_data->digest, calc.digest,
> -			    sizeof(calc.digest));
> +		rc = crypto_memneq(xattr_data->digest, digest.digest,
> +				   SHA1_DIGEST_SIZE);
>  		if (rc)
>  			rc = -EINVAL;
>  		break;
>  	case EVM_IMA_XATTR_DIGSIG:
>  	case EVM_XATTR_PORTABLE_DIGSIG:
> +		hdr = (struct signature_v2_hdr *)xattr_data;
> +		digest.hdr.algo = hdr->hash_algo;
>  		rc = evm_calc_hash(dentry, xattr_name, xattr_value,
> -				   xattr_value_len, xattr_data->type,
> -				   calc.digest);
> +				   xattr_value_len, xattr_data->type, &digest);
>  		if (rc)
>  			break;
>  		rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
>  					(const char *)xattr_data, xattr_len,
> -					calc.digest, sizeof(calc.digest));
> +					digest.digest, digest.hdr.length);
>  		if (!rc) {
>  			inode = d_backing_inode(dentry);
>
Matthew Garrett May 29, 2018, 6:26 p.m. UTC | #2 
On Fri, May 18, 2018 at 9:03 AM Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:

> On Thu, 2018-05-17 at 15:09 -0700, Matthew Garrett wrote:
> > Oh bother - I think I see what's wrong. Does this version work better?
> > I'm afraid I only tested against signatures rather than HMACs, and I was
> > generating a raw SHA1 rather than an HMAC :(

> That's a lot better!

> FYI, Wang Junwen reported a problem with enabling EVM with just the
> immutable and portable keys.  Without trusted keys enabled, SHA1 isn't
> being built into the kernel.  Loading the SHA1 kernel module fails.
>   Without knowing apriori which hash algorithms need to be builtin is a
> problem.

It looks like Kconfig is selecting CRYPTO_SHA1 when EVM is enabled, and
since that's a bool it should be forcing it to be built-in? I can't see a
good way of extending that generally, unfortunately. Is the problem with
loading the module that you're enforcing an IMA policy before loading it?
Matthew Garrett May 30, 2018, 6:29 p.m. UTC | #3 
On Tue, May 29, 2018 at 11:25 PM Wang,Junwen <wangjunwen@baidu.com> wrote:
> if we need fix this problem
> 1. load the hash algorithm at initial time instead of runtime
> OR
> 2. avoid the crypto_alloc_shash try to load modules in init_desc

The outcome here is presumably going to be failure regardless - if
appraisal is required and the hash module is unavailable, failing to load
the module won't result in deadlock but will result in an unusable machine?
I think the only way this can work is to ensure the crypto modules are
available before a policy is enabled, but let me look to see if there's a
way to at least make the failure clean and more debuggable.
diff mbox

Patch

diff --git a/security/integrity/evm/evm.h b/security/integrity/evm/evm.h
index 45c4a89c02ff..a8289fbf2f0c 100644
--- a/security/integrity/evm/evm.h
+++ b/security/integrity/evm/evm.h
@@ -42,6 +42,11 @@  extern struct crypto_shash *hash_tfm;
 /* List of EVM protected security xattrs */
 extern char *evm_config_xattrnames[];
 
+struct evm_digest {
+	struct ima_digest_data hdr;
+	char digest[IMA_MAX_DIGEST_SIZE];
+} __packed;
+
 int evm_init_key(void);
 int evm_update_evmxattr(struct dentry *dentry,
 			const char *req_xattr_name,
@@ -49,10 +54,11 @@  int evm_update_evmxattr(struct dentry *dentry,
 			size_t req_xattr_value_len);
 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
 		  const char *req_xattr_value,
-		  size_t req_xattr_value_len, char *digest);
+		  size_t req_xattr_value_len, struct evm_digest *data);
 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
 		  const char *req_xattr_value,
-		  size_t req_xattr_value_len, char type, char *digest);
+		  size_t req_xattr_value_len, char type,
+		  struct evm_digest *data);
 int evm_init_hmac(struct inode *inode, const struct xattr *xattr,
 		  char *hmac_val);
 int evm_init_secfs(void);
diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index a46fba322340..eb87d40c62a5 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -21,6 +21,7 @@ 
 #include <linux/evm.h>
 #include <keys/encrypted-type.h>
 #include <crypto/hash.h>
+#include <crypto/hash_info.h>
 #include "evm.h"
 
 #define EVMKEY "evm-key"
@@ -29,7 +30,7 @@  static unsigned char evmkey[MAX_KEY_SIZE];
 static int evmkey_len = MAX_KEY_SIZE;
 
 struct crypto_shash *hmac_tfm;
-struct crypto_shash *hash_tfm;
+static struct crypto_shash *evm_tfm[HASH_ALGO__LAST];
 
 static DEFINE_MUTEX(mutex);
 
@@ -38,7 +39,6 @@  static DEFINE_MUTEX(mutex);
 static unsigned long evm_set_key_flags;
 
 static char * const evm_hmac = "hmac(sha1)";
-static char * const evm_hash = "sha1";
 
 /**
  * evm_set_key() - set EVM HMAC key from the kernel
@@ -74,10 +74,10 @@  int evm_set_key(void *key, size_t keylen)
 }
 EXPORT_SYMBOL_GPL(evm_set_key);
 
-static struct shash_desc *init_desc(char type)
+static struct shash_desc *init_desc(char type, uint8_t hash_algo)
 {
 	long rc;
-	char *algo;
+	const char *algo;
 	struct crypto_shash **tfm;
 	struct shash_desc *desc;
 
@@ -89,8 +89,8 @@  static struct shash_desc *init_desc(char type)
 		tfm = &hmac_tfm;
 		algo = evm_hmac;
 	} else {
-		tfm = &hash_tfm;
-		algo = evm_hash;
+		tfm = &evm_tfm[hash_algo];
+		algo = hash_algo_name[hash_algo];
 	}
 
 	if (*tfm == NULL) {
@@ -186,10 +186,10 @@  static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
  * each xattr, but attempt to re-use the previously allocated memory.
  */
 static int evm_calc_hmac_or_hash(struct dentry *dentry,
-				const char *req_xattr_name,
-				const char *req_xattr_value,
-				size_t req_xattr_value_len,
-				char type, char *digest)
+				 const char *req_xattr_name,
+				 const char *req_xattr_value,
+				 size_t req_xattr_value_len,
+				 uint8_t type, struct evm_digest *data)
 {
 	struct inode *inode = d_backing_inode(dentry);
 	struct shash_desc *desc;
@@ -203,10 +203,12 @@  static int evm_calc_hmac_or_hash(struct dentry *dentry,
 	if (!(inode->i_opflags & IOP_XATTR))
 		return -EOPNOTSUPP;
 
-	desc = init_desc(type);
+	desc = init_desc(type, data->hdr.algo);
 	if (IS_ERR(desc))
 		return PTR_ERR(desc);
 
+	data->hdr.length = crypto_shash_digestsize(desc->tfm);
+
 	error = -ENODATA;
 	for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
 		bool is_ima = false;
@@ -238,7 +240,7 @@  static int evm_calc_hmac_or_hash(struct dentry *dentry,
 		if (is_ima)
 			ima_present = true;
 	}
-	hmac_add_misc(desc, inode, type, digest);
+	hmac_add_misc(desc, inode, type, data->digest);
 
 	/* Portable EVM signatures must include an IMA hash */
 	if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
@@ -251,18 +253,18 @@  static int evm_calc_hmac_or_hash(struct dentry *dentry,
 
 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
 		  const char *req_xattr_value, size_t req_xattr_value_len,
-		  char *digest)
+		  struct evm_digest *data)
 {
 	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
-			       req_xattr_value_len, EVM_XATTR_HMAC, digest);
+				    req_xattr_value_len, EVM_XATTR_HMAC, data);
 }
 
 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
 		  const char *req_xattr_value, size_t req_xattr_value_len,
-		  char type, char *digest)
+		  char type, struct evm_digest *data)
 {
 	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
-				     req_xattr_value_len, type, digest);
+				     req_xattr_value_len, type, data);
 }
 
 static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
@@ -302,7 +304,7 @@  int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
 			const char *xattr_value, size_t xattr_value_len)
 {
 	struct inode *inode = d_backing_inode(dentry);
-	struct evm_ima_xattr_data xattr_data;
+	struct evm_digest data;
 	int rc = 0;
 
 	/*
@@ -315,13 +317,14 @@  int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
 	if (rc)
 		return -EPERM;
 
+	data.hdr.algo = HASH_ALGO_SHA1;
 	rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
-			   xattr_value_len, xattr_data.digest);
+			   xattr_value_len, &data);
 	if (rc == 0) {
-		xattr_data.type = EVM_XATTR_HMAC;
+		data.hdr.xattr.sha1.type = EVM_XATTR_HMAC;
 		rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
-					   &xattr_data,
-					   sizeof(xattr_data), 0);
+					   &data.hdr.xattr.data[1],
+					   SHA1_DIGEST_SIZE + 1, 0);
 	} else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
 		rc = __vfs_removexattr(dentry, XATTR_NAME_EVM);
 	}
@@ -333,7 +336,7 @@  int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 {
 	struct shash_desc *desc;
 
-	desc = init_desc(EVM_XATTR_HMAC);
+	desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
 	if (IS_ERR(desc)) {
 		pr_info("init_desc failed\n");
 		return PTR_ERR(desc);
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 9ea9c19a545c..88ea9c1962d6 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -25,6 +25,7 @@ 
 #include <linux/magic.h>
 
 #include <crypto/hash.h>
+#include <crypto/hash_info.h>
 #include <crypto/algapi.h>
 #include "evm.h"
 
@@ -122,8 +123,9 @@  static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 					     struct integrity_iint_cache *iint)
 {
 	struct evm_ima_xattr_data *xattr_data = NULL;
-	struct evm_ima_xattr_data calc;
+	struct signature_v2_hdr *hdr;
 	enum integrity_status evm_status = INTEGRITY_PASS;
+	struct evm_digest digest;
 	struct inode *inode;
 	int rc, xattr_len;
 
@@ -159,25 +161,28 @@  static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 			evm_status = INTEGRITY_FAIL;
 			goto out;
 		}
+
+		digest.hdr.algo = HASH_ALGO_SHA1;
 		rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
-				   xattr_value_len, calc.digest);
+				   xattr_value_len, &digest);
 		if (rc)
 			break;
-		rc = crypto_memneq(xattr_data->digest, calc.digest,
-			    sizeof(calc.digest));
+		rc = crypto_memneq(xattr_data->digest, digest.digest,
+				   SHA1_DIGEST_SIZE);
 		if (rc)
 			rc = -EINVAL;
 		break;
 	case EVM_IMA_XATTR_DIGSIG:
 	case EVM_XATTR_PORTABLE_DIGSIG:
+		hdr = (struct signature_v2_hdr *)xattr_data;
+		digest.hdr.algo = hdr->hash_algo;
 		rc = evm_calc_hash(dentry, xattr_name, xattr_value,
-				   xattr_value_len, xattr_data->type,
-				   calc.digest);
+				   xattr_value_len, xattr_data->type, &digest);
 		if (rc)
 			break;
 		rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
 					(const char *)xattr_data, xattr_len,
-					calc.digest, sizeof(calc.digest));
+					digest.digest, digest.hdr.length);
 		if (!rc) {
 			inode = d_backing_inode(dentry);