ecryptfs: fix dereference of NULL user_key_payload

PATCH New Eric Biggers 1 participant 3 messages Oct 9, 2017

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Stable branch Security (LSM) Keys/keyrings Ecrypt file system

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Eric Biggers

author

2017-10-09 19:51 UTC #0 lore raw

PATCH v2 1/3 ecryptfs: fix dereference of NULL user_key_payload

From: Eric Biggers <[email protected]>

In eCryptfs, we failed to verify that the authentication token keys are not revoked before dereferencing their payloads, which is problematic because the payload of a revoked key is NULL. request_key() *does* skip revoked keys, but there is still a window where the key can be revoked before we acquire the key semaphore.

Fix it by updating ecryptfs_get_key_payload_data() to return -EKEYREVOKED if the key payload is NULL. For completeness we check this for "encrypted" keys as well as "user" keys, although encrypted keys cannot be revoked currently.

Alternatively we could use key_validate(), but since we'll also need to fix ecryptfs_get_key_payload_data() to validate the payload length, it seems appropriate to just check the payload pointer.

Fixes 237fead61998 ("[PATCH] ecryptfs: fs/Makefile and fs/Kconfig")

Reviewed-by James Morris <[email protected]>

Cc <[email protected]> [v2.6.19+]

Cc Michael Halcrow <[email protected]>

Signed-off-by Eric Biggers <[email protected]>

---

Changed since v1: added Reviewed-by and resent in series with just the ecryptfs patches. Can this please be taken through the ecryptfs tree?

 fs/ecryptfs/ecryptfs_kernel.h | 24 +++++++++++++++++-------
 fs/ecryptfs/keystore.c        |  9 ++++++++-
 2 files changed, 25 insertions(+), 8 deletions(-)

fs/ecryptfs/ecryptfs_kernel.h +17 -7

index 9c351bf757b2..3fbc0ff79699 100644
@@ -84,11 +84,16 @@ struct ecryptfs_page_crypt_context {
 static inline struct ecryptfs_auth_tok *
 ecryptfs_get_encrypted_key_payload_data(struct key *key)
 {
-	if (key->type = &key_type_encrypted)
-		return (struct ecryptfs_auth_tok *)
-			(&((struct encrypted_key_payload *)key->payload.data[0])->payload_data);
-	else
+	struct encrypted_key_payload *payload;
+
+	if (key->type != &key_type_encrypted)
 		return NULL;
+
+	payload = key->payload.data[0];
+	if (!payload)
+		return ERR_PTR(-EKEYREVOKED);
+
+	return (struct ecryptfs_auth_tok *)payload->payload_data;
 }
 
 static inline struct key *ecryptfs_get_encrypted_key(char *sig)

@@ -114,12 +119,17 @@ static inline struct ecryptfs_auth_tok *
 ecryptfs_get_key_payload_data(struct key *key)
 {
 	struct ecryptfs_auth_tok *auth_tok;
+	struct user_key_payload *ukp;
 
 	auth_tok = ecryptfs_get_encrypted_key_payload_data(key);
-	if (!auth_tok)
-		return (struct ecryptfs_auth_tok *)user_key_payload_locked(key)->data;
-	else
+	if (auth_tok)
 		return auth_tok;
+
+	ukp = user_key_payload_locked(key);
+	if (!ukp)
+		return ERR_PTR(-EKEYREVOKED);
+
+	return (struct ecryptfs_auth_tok *)ukp->data;
 }
 
 #define ECRYPTFS_MAX_KEYSET_SIZE 1024

fs/ecryptfs/keystore.c +8 -1

index 3cf1546dca82..fa218cd64f74 100644
@@ -459,7 +459,8 @@ static int ecryptfs_verify_version(u16 version)
  * @auth_tok_key: key containing the authentication token
  * @auth_tok: authentication token
  *
- * Returns zero on valid auth tok; -EINVAL otherwise
+ * Returns zero on valid auth tok; -EINVAL if the payload is invalid; or
+ * -EKEYREVOKED if the key was revoked before we acquired its semaphore.
  */
 static int
 ecryptfs_verify_auth_tok_from_key(struct key *auth_tok_key,

@@ -468,6 +469,12 @@ ecryptfs_verify_auth_tok_from_key(struct key *auth_tok_key,
 	int rc = 0;
 
 	(*auth_tok) = ecryptfs_get_key_payload_data(auth_tok_key);
+	if (IS_ERR(*auth_tok)) {
+		rc = PTR_ERR(*auth_tok);
+		*auth_tok = NULL;
+		goto out;
+	}
+
 	if (ecryptfs_verify_version((*auth_tok)->version)) {
 		printk(KERN_ERR "Data structure version mismatch. Userspace "
 		       "tools must match eCryptfs kernel module with major "

Signature · 1 line

2.14.2.920.gcf0c67979c-goog

Eric Biggers

author

2017-10-09 19:51 UTC #1 lore raw

PATCH v2 2/3 ecryptfs: fix out-of-bounds read of key payload

From: Eric Biggers <[email protected]>

eCryptfs blindly casts the user-supplied key payload to a 'struct ecryptfs_auth_tok' without validating that the payload does, in fact, have the size of a 'struct ecryptfs_auth_tok'. Fix it.

Fixes 237fead61998 ("[PATCH] ecryptfs: fs/Makefile and fs/Kconfig")

Reviewed-by James Morris <[email protected]>

Cc <[email protected]> [v2.6.19+]

Cc Michael Halcrow <[email protected]>

Signed-off-by Eric Biggers <[email protected]>

---

Changed since v1: added Reviewed-by and resent in series with just the ecryptfs patches. Can this please be taken through the ecryptfs tree?

 fs/ecryptfs/ecryptfs_kernel.h | 6 ++++++
 fs/ecryptfs/keystore.c        | 4 ++++
 2 files changed, 10 insertions(+)

fs/ecryptfs/ecryptfs_kernel.h +6 -0

index 3fbc0ff79699..945844d5f0ef 100644
@@ -93,6 +93,9 @@ ecryptfs_get_encrypted_key_payload_data(struct key *key)
 	if (!payload)
 		return ERR_PTR(-EKEYREVOKED);
 
+	if (payload->payload_datalen != sizeof(struct ecryptfs_auth_tok))
+		return ERR_PTR(-EINVAL);
+
 	return (struct ecryptfs_auth_tok *)payload->payload_data;
 }

@@ -129,6 +132,9 @@ ecryptfs_get_key_payload_data(struct key *key)
 	if (!ukp)
 		return ERR_PTR(-EKEYREVOKED);
 
+	if (ukp->datalen != sizeof(struct ecryptfs_auth_tok))
+		return ERR_PTR(-EINVAL);
+
 	return (struct ecryptfs_auth_tok *)ukp->data;
 }

fs/ecryptfs/keystore.c +4 -0

index fa218cd64f74..95e20ab67df3 100644
@@ -471,6 +471,10 @@ ecryptfs_verify_auth_tok_from_key(struct key *auth_tok_key,
 	(*auth_tok) = ecryptfs_get_key_payload_data(auth_tok_key);
 	if (IS_ERR(*auth_tok)) {
 		rc = PTR_ERR(*auth_tok);
+		if (rc = -EINVAL) {
+			ecryptfs_printk(KERN_ERR,
+					"Authentication token payload has wrong length\n");
+		}
 		*auth_tok = NULL;
 		goto out;
 	}

Signature · 1 line

2.14.2.920.gcf0c67979c-goog

Eric Biggers

author

2017-10-09 19:51 UTC #2 lore raw

PATCH v2 3/3 ecryptfs: move key payload accessor functions into keystore.c

In reply to Eric Biggers

From: Eric Biggers <[email protected]>

As experience has shown, accessing the 'struct key' payload is very error-prone, since we need to hold the key semaphore and properly validate everything. Fortunately eCryptfs only does it from one place, in ecryptfs_verify_auth_tok_from_key() in keystore.c. Therefore, move the payload accessor functions like ecryptfs_get_key_payload_data() out of ecryptfs_kernel.h and into keystore.c so that people might be less tempted to use them directly.

Reviewed-by James Morris <[email protected]>

Cc Michael Halcrow <[email protected]>

Signed-off-by Eric Biggers <[email protected]>

---

Changed since v1: added Reviewed-by and resent in series with just the ecryptfs patches. Can this please be taken through the ecryptfs tree?

 fs/ecryptfs/ecryptfs_kernel.h | 60 -------------------------------------------
 fs/ecryptfs/keystore.c        | 60 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+), 60 deletions(-)

fs/ecryptfs/ecryptfs_kernel.h +0 ~~-60~~

index 945844d5f0ef..f2e339a6f9e9 100644
@@ -29,8 +29,6 @@
 #define ECRYPTFS_KERNEL_H
 
 #include <crypto/skcipher.h>
-#include <keys/user-type.h>
-#include <keys/encrypted-type.h>
 #include <linux/fs.h>
 #include <linux/fs_stack.h>
 #include <linux/namei.h>

@@ -80,64 +78,6 @@ struct ecryptfs_page_crypt_context {
 	} param;
 };
 
-#if defined(CONFIG_ENCRYPTED_KEYS) || defined(CONFIG_ENCRYPTED_KEYS_MODULE)
-static inline struct ecryptfs_auth_tok *
-ecryptfs_get_encrypted_key_payload_data(struct key *key)
-{
-	struct encrypted_key_payload *payload;
-
-	if (key->type != &key_type_encrypted)
-		return NULL;
-
-	payload = key->payload.data[0];
-	if (!payload)
-		return ERR_PTR(-EKEYREVOKED);
-
-	if (payload->payload_datalen != sizeof(struct ecryptfs_auth_tok))
-		return ERR_PTR(-EINVAL);
-
-	return (struct ecryptfs_auth_tok *)payload->payload_data;
-}
-
-static inline struct key *ecryptfs_get_encrypted_key(char *sig)
-{
-	return request_key(&key_type_encrypted, sig, NULL);
-}
-
-#else
-static inline struct ecryptfs_auth_tok *
-ecryptfs_get_encrypted_key_payload_data(struct key *key)
-{
-	return NULL;
-}
-
-static inline struct key *ecryptfs_get_encrypted_key(char *sig)
-{
-	return ERR_PTR(-ENOKEY);
-}
-
-#endif /* CONFIG_ENCRYPTED_KEYS */
-
-static inline struct ecryptfs_auth_tok *
-ecryptfs_get_key_payload_data(struct key *key)
-{
-	struct ecryptfs_auth_tok *auth_tok;
-	struct user_key_payload *ukp;
-
-	auth_tok = ecryptfs_get_encrypted_key_payload_data(key);
-	if (auth_tok)
-		return auth_tok;
-
-	ukp = user_key_payload_locked(key);
-	if (!ukp)
-		return ERR_PTR(-EKEYREVOKED);
-
-	if (ukp->datalen != sizeof(struct ecryptfs_auth_tok))
-		return ERR_PTR(-EINVAL);
-
-	return (struct ecryptfs_auth_tok *)ukp->data;
-}
-
 #define ECRYPTFS_MAX_KEYSET_SIZE 1024
 #define ECRYPTFS_MAX_CIPHER_NAME_SIZE 31
 #define ECRYPTFS_MAX_NUM_ENC_KEYS 64

fs/ecryptfs/keystore.c +60 -0

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