1 files changed, 57 insertions, 16 deletions

diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 9b898c969558..434ed9defd3a 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -798,6 +798,21 @@ error:
 }
 
 /*
+ * Call the read method
+ */
+static long __keyctl_read_key(struct key *key, char *buffer, size_t buflen)
+{
+	long ret;
+
+	down_read(&key->sem);
+	ret = key_validate(key);
+	if (ret == 0)
+		ret = key->type->read(key, buffer, buflen);
+	up_read(&key->sem);
+	return ret;
+}
+
+/*
  * Read a key's payload.
  *
  * The key must either grant the caller Read permission, or it must grant the
@@ -812,26 +827,27 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)
 	struct key *key;
 	key_ref_t key_ref;
 	long ret;
+	char *key_data;
 
 	/* find the key first */
 	key_ref = lookup_user_key(keyid, 0, 0);
 	if (IS_ERR(key_ref)) {
 		ret = -ENOKEY;
-		goto error;
+		goto out;
 	}
 
 	key = key_ref_to_ptr(key_ref);
 
 	ret = key_read_state(key);
 	if (ret < 0)
-		goto error2; /* Negatively instantiated */
+		goto key_put_out; /* Negatively instantiated */
 
 	/* see if we can read it directly */
 	ret = key_permission(key_ref, KEY_NEED_READ);
 	if (ret == 0)
 		goto can_read_key;
 	if (ret != -EACCES)
-		goto error2;
+		goto key_put_out;
 
 	/* we can't; see if it's searchable from this process's keyrings
 	 * - we automatically take account of the fact that it may be
@@ -839,26 +855,51 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)
 	 */
 	if (!is_key_possessed(key_ref)) {
 		ret = -EACCES;
-		goto error2;
+		goto key_put_out;
 	}
 
 	/* the key is probably readable - now try to read it */
 can_read_key:
-	ret = -EOPNOTSUPP;
-	if (key->type->read) {
-		/* Read the data with the semaphore held (since we might sleep)
-		 * to protect against the key being updated or revoked.
-		 */
-		down_read(&key->sem);
-		ret = key_validate(key);
-		if (ret == 0)
-			ret = key->type->read(key, buffer, buflen);
-		up_read(&key->sem);
+	if (!key->type->read) {
+		ret = -EOPNOTSUPP;
+		goto key_put_out;
 	}
 
-error2:
+	if (!buffer || !buflen) {
+		/* Get the key length from the read method */
+		ret = __keyctl_read_key(key, NULL, 0);
+		goto key_put_out;
+	}
+
+	/*
+	 * Read the data with the semaphore held (since we might sleep)
+	 * to protect against the key being updated or revoked.
+	 *
+	 * Allocating a temporary buffer to hold the keys before
+	 * transferring them to user buffer to avoid potential
+	 * deadlock involving page fault and mmap_sem.
+	 */
+	key_data = kmalloc(buflen, GFP_KERNEL);
+
+	if (!key_data) {
+		ret = -ENOMEM;
+		goto key_put_out;
+	}
+	ret = __keyctl_read_key(key, key_data, buflen);
+
+	/*
+	 * Read methods will just return the required length without
+	 * any copying if the provided length isn't large enough.
+	 */
+	if (ret > 0 && ret <= buflen) {
+		if (copy_to_user(buffer, key_data, ret))
+			ret = -EFAULT;
+	}
+	kzfree(key_data);
+
+key_put_out:
 	key_put(key);
-error:
+out:
 	return ret;
 }