qcow2/qcow: protect against uninitialized encryption key

When a qcow[2] file is opened, if the header reports an
encryption method, this is used to set the 'crypt_method_header'
field on the BDRVQcow[2]State struct, and the 'encrypted' flag
in the BDRVState struct.

When doing I/O operations, the 'crypt_method' field on the
BDRVQcow[2]State struct is checked to determine if encryption
needs to be applied.

The crypt_method_header value is copied into crypt_method when
the bdrv_set_key() method is called.

The QEMU code which opens a block device is expected to always
do a check

   if (bdrv_is_encrypted(bs)) {
       bdrv_set_key(bs, ....key...);
   }

If code forgets to do this, then 'crypt_method' is never set
and so when I/O is performed, QEMU writes plain text data
into a sector which is expected to contain cipher text, or
when reading, will return cipher text instead of plain
text.

Change the qcow[2] code to consult bs->encrypted when deciding
whether encryption is required, and assert(s->crypt_method)
to protect against cases where the caller forgets to set the
encryption key.

Also put an assert in the set_key methods to protect against
the case where the caller sets an encryption key on a block
device that does not have encryption

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/block/qcow.c b/block/qcow.c
index ab893284d2..911e59fd0b 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -269,6 +269,7 @@ static int qcow_set_key(BlockDriverState *bs, const char *key)
     for(i = 0;i < len;i++) {
         keybuf[i] = key[i];
     }
+    assert(bs->encrypted);
     s->crypt_method = s->crypt_method_header;
 
     if (AES_set_encrypt_key(keybuf, 128, &s->aes_encrypt_key) != 0)
@@ -411,9 +412,10 @@ static uint64_t get_cluster_offset(BlockDriverState *bs,
                 bdrv_truncate(bs->file, cluster_offset + s->cluster_size);
                 /* if encrypted, we must initialize the cluster
                    content which won't be written */
-                if (s->crypt_method &&
+                if (bs->encrypted &&
                     (n_end - n_start) < s->cluster_sectors) {
                     uint64_t start_sect;
+                    assert(s->crypt_method);
                     start_sect = (offset & ~(s->cluster_size - 1)) >> 9;
                     memset(s->cluster_data + 512, 0x00, 512);
                     for(i = 0; i < s->cluster_sectors; i++) {
@@ -590,7 +592,8 @@ static coroutine_fn int qcow_co_readv(BlockDriverState *bs, int64_t sector_num,
             if (ret < 0) {
                 break;
             }
-            if (s->crypt_method) {
+            if (bs->encrypted) {
+                assert(s->crypt_method);
                 encrypt_sectors(s, sector_num, buf, buf,
                                 n, 0,
                                 &s->aes_decrypt_key);
@@ -661,7 +664,8 @@ static coroutine_fn int qcow_co_writev(BlockDriverState *bs, int64_t sector_num,
             ret = -EIO;
             break;
         }
-        if (s->crypt_method) {
+        if (bs->encrypted) {
+            assert(s->crypt_method);
             if (!cluster_data) {
                 cluster_data = g_malloc0(s->cluster_size);
             }