Security: Keys: Big keys stored encrypted

Solved TODO task: big keys saved to shmem file are now stored encrypted.
The encryption key is randomly generated and saved to payload[big_key_data].

Signed-off-by: Kirill Marinushkin <k.marinushkin@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>

2 files changed, 184 insertions, 18 deletions

diff --git a/security/keys/Kconfig b/security/keys/Kconfig
index fe4d74e126a7..45828095080d 100644
--- a/security/keys/Kconfig
+++ b/security/keys/Kconfig
@@ -41,6 +41,10 @@ config BIG_KEYS
         bool "Large payload keys"
         depends on KEYS
         depends on TMPFS
+        select CRYPTO
+        select CRYPTO_AES
+        select CRYPTO_ECB
+        select CRYPTO_RNG
         help
           This option provides support for holding large keys within the kernel
           (for example Kerberos ticket caches).  The data may be stored out to
diff --git a/security/keys/big_key.c b/security/keys/big_key.c
index c721e398893a..9e443fccad4c 100644
--- a/security/keys/big_key.c
+++ b/security/keys/big_key.c
@@ -14,8 +14,10 @@
 #include <linux/file.h>
 #include <linux/shmem_fs.h>
 #include <linux/err.h>
+#include <linux/scatterlist.h>
 #include <keys/user-type.h>
 #include <keys/big_key-type.h>
+#include <crypto/rng.h>
 
 /*
  * Layout of key payload words.
@@ -28,6 +30,14 @@ enum {
 };
 
 /*
+ * Crypto operation with big_key data
+ */
+enum big_key_op {
+        BIG_KEY_ENC,
+        BIG_KEY_DEC,
+};
+
+/*
  * If the data is under this limit, there's no point creating a shm file to
  * hold it as the permanently resident metadata for the shmem fs will be at
  * least as large as the data.
@@ -35,6 +45,11 @@ enum {
 #define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
 
 /*
+ * Key size for big_key data encryption
+ */
+#define ENC_KEY_SIZE    16
+
+/*
  * big_key defined keys take an arbitrary string as the description and an
  * arbitrary blob of data as the payload
  */
@@ -50,12 +65,62 @@ struct key_type key_type_big_key = {
 };
 
 /*
+ * Crypto names for big_key data encryption
+ */
+static const char big_key_rng_name[] = "stdrng";
+static const char big_key_alg_name[] = "ecb(aes)";
+
+/*
+ * Crypto algorithms for big_key data encryption
+ */
+static struct crypto_rng *big_key_rng;
+static struct crypto_blkcipher *big_key_blkcipher;
+
+/*
+ * Generate random key to encrypt big_key data
+ */
+static inline int big_key_gen_enckey(u8 *key)
+{
+        return crypto_rng_get_bytes(big_key_rng, key, ENC_KEY_SIZE);
+}
+
+/*
+ * Encrypt/decrypt big_key data
+ */
+static int big_key_crypt(enum big_key_op op, u8 *data, size_t datalen, u8 *key)
+{
+        int ret = -EINVAL;
+        struct scatterlist sgio;
+        struct blkcipher_desc desc;
+
+        if (crypto_blkcipher_setkey(big_key_blkcipher, key, ENC_KEY_SIZE)) {
+                ret = -EAGAIN;
+                goto error;
+        }
+
+        desc.flags = 0;
+        desc.tfm = big_key_blkcipher;
+
+        sg_init_one(&sgio, data, datalen);
+
+        if (op == BIG_KEY_ENC)
+                ret = crypto_blkcipher_encrypt(&desc, &sgio, &sgio, datalen);
+        else
+                ret = crypto_blkcipher_decrypt(&desc, &sgio, &sgio, datalen);
+
+error:
+        return ret;
+}
+
+/*
  * Preparse a big key
  */
 int big_key_preparse(struct key_preparsed_payload *prep)
 {
         struct path *path = (struct path *)&prep->payload.data[big_key_path];
         struct file *file;
+        u8 *enckey;
+        u8 *data = NULL;
         ssize_t written;
         size_t datalen = prep->datalen;
         int ret;
@@ -73,16 +138,43 @@ int big_key_preparse(struct key_preparsed_payload *prep)
                 /* Create a shmem file to store the data in.  This will permit the data
                  * to be swapped out if needed.
                  *
-                 * TODO: Encrypt the stored data with a temporary key.
+                 * File content is stored encrypted with randomly generated key.
                  */
-                file = shmem_kernel_file_setup("", datalen, 0);
+                size_t enclen = ALIGN(datalen, crypto_blkcipher_blocksize(big_key_blkcipher));
+
+                /* prepare aligned data to encrypt */
+                data = kmalloc(enclen, GFP_KERNEL);
+                if (!data)
+                        return -ENOMEM;
+
+                memcpy(data, prep->data, datalen);
+                memset(data + datalen, 0x00, enclen - datalen);
+
+                /* generate random key */
+                enckey = kmalloc(ENC_KEY_SIZE, GFP_KERNEL);
+                if (!enckey) {
+                        ret = -ENOMEM;
+                        goto error;
+                }
+
+                ret = big_key_gen_enckey(enckey);
+                if (ret)
+                        goto err_enckey;
+
+                /* encrypt aligned data */
+                ret = big_key_crypt(BIG_KEY_ENC, data, enclen, enckey);
+                if (ret)
+                        goto err_enckey;
+
+                /* save aligned data to file */
+                file = shmem_kernel_file_setup("", enclen, 0);
                 if (IS_ERR(file)) {
                         ret = PTR_ERR(file);
-                        goto error;
+                        goto err_enckey;
                 }
 
-                written = kernel_write(file, prep->data, prep->datalen, 0);
-                if (written != datalen) {
+                written = kernel_write(file, data, enclen, 0);
+                if (written != enclen) {
                         ret = written;
                         if (written >= 0)
                                 ret = -ENOMEM;
@@ -92,12 +184,15 @@ int big_key_preparse(struct key_preparsed_payload *prep)
                 /* Pin the mount and dentry to the key so that we can open it again
                  * later
                  */
+                prep->payload.data[big_key_data] = enckey;
                 *path = file->f_path;
                 path_get(path);
                 fput(file);
+                kfree(data);
         } else {
                 /* Just store the data in a buffer */
                 void *data = kmalloc(datalen, GFP_KERNEL);
+
                 if (!data)
                         return -ENOMEM;
 
@@ -108,7 +203,10 @@ int big_key_preparse(struct key_preparsed_payload *prep)
 
 err_fput:
         fput(file);
+err_enckey:
+        kfree(enckey);
 error:
+        kfree(data);
         return ret;
 }
 
@@ -119,10 +217,10 @@ void big_key_free_preparse(struct key_preparsed_payload *prep)
 {
         if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
                 struct path *path = (struct path *)&prep->payload.data[big_key_path];
+
                 path_put(path);
-        } else {
-                kfree(prep->payload.data[big_key_data]);
         }
+        kfree(prep->payload.data[big_key_data]);
 }
 
 /*
@@ -147,15 +245,15 @@ void big_key_destroy(struct key *key)
 {
         size_t datalen = (size_t)key->payload.data[big_key_len];
 
-        if (datalen) {
+        if (datalen > BIG_KEY_FILE_THRESHOLD) {
                 struct path *path = (struct path *)&key->payload.data[big_key_path];
+
                 path_put(path);
                 path->mnt = NULL;
                 path->dentry = NULL;
-        } else {
-                kfree(key->payload.data[big_key_data]);
-                key->payload.data[big_key_data] = NULL;
         }
+        kfree(key->payload.data[big_key_data]);
+        key->payload.data[big_key_data] = NULL;
 }
 
 /*
@@ -188,17 +286,41 @@ long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
         if (datalen > BIG_KEY_FILE_THRESHOLD) {
                 struct path *path = (struct path *)&key->payload.data[big_key_path];
                 struct file *file;
-                loff_t pos;
+                u8 *data;
+                u8 *enckey = (u8 *)key->payload.data[big_key_data];
+                size_t enclen = ALIGN(datalen, crypto_blkcipher_blocksize(big_key_blkcipher));
+
+                data = kmalloc(enclen, GFP_KERNEL);
+                if (!data)
+                        return -ENOMEM;
 
                 file = dentry_open(path, O_RDONLY, current_cred());
-                if (IS_ERR(file))
-                        return PTR_ERR(file);
+                if (IS_ERR(file)) {
+                        ret = PTR_ERR(file);
+                        goto error;
+                }
 
-                pos = 0;
-                ret = vfs_read(file, buffer, datalen, &pos);
-                fput(file);
-                if (ret >= 0 && ret != datalen)
+                /* read file to kernel and decrypt */
+                ret = kernel_read(file, 0, data, enclen);
+                if (ret >= 0 && ret != enclen) {
                         ret = -EIO;
+                        goto err_fput;
+                }
+
+                ret = big_key_crypt(BIG_KEY_DEC, data, enclen, enckey);
+                if (ret)
+                        goto err_fput;
+
+                ret = datalen;
+
+                /* copy decrypted data to user */
+                if (copy_to_user(buffer, data, datalen) != 0)
+                        ret = -EFAULT;
+
+err_fput:
+                fput(file);
+error:
+                kfree(data);
         } else {
                 ret = datalen;
                 if (copy_to_user(buffer, key->payload.data[big_key_data],
@@ -209,8 +331,48 @@ long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
         return ret;
 }
 
+/*
+ * Register key type
+ */
 static int __init big_key_init(void)
 {
         return register_key_type(&key_type_big_key);
 }
+
+/*
+ * Initialize big_key crypto and RNG algorithms
+ */
+static int __init big_key_crypto_init(void)
+{
+        int ret = -EINVAL;
+
+        /* init RNG */
+        big_key_rng = crypto_alloc_rng(big_key_rng_name, 0, 0);
+        if (IS_ERR(big_key_rng)) {
+                big_key_rng = NULL;
+                return -EFAULT;
+        }
+
+        /* seed RNG */
+        ret = crypto_rng_reset(big_key_rng, NULL, crypto_rng_seedsize(big_key_rng));
+        if (ret)
+                goto error;
+
+        /* init block cipher */
+        big_key_blkcipher = crypto_alloc_blkcipher(big_key_alg_name, 0, 0);
+        if (IS_ERR(big_key_blkcipher)) {
+                big_key_blkcipher = NULL;
+                ret = -EFAULT;
+                goto error;
+        }
+
+        return 0;
+
+error:
+        crypto_free_rng(big_key_rng);
+        big_key_rng = NULL;
+        return ret;
+}
+
 device_initcall(big_key_init);
+late_initcall(big_key_crypto_init);