block: Guard against NULL bs->drv

We currently do not guard everywhere against a NULL bs->drv where we
should be doing so.  Most of the places fixed here just do not care
about that case at all.

Some care implicitly, e.g. through a prior function call to
bdrv_getlength() which would always fail for an ejected BDS.  Add an
assert there to make it more obvious.

Other places seem to care, but do so insufficiently: Freeing clusters in
a qcow2 image is an error-free operation, but it may leave the image in
an unusable state anyway.  Giving qcow2_free_clusters() an error code is
not really viable, it is much easier to note that bs->drv may be NULL
even after a successful driver call.  This concerns bdrv_co_flush(), and
the way the check is added to bdrv_co_pdiscard() (in every iteration
instead of only once).

Finally, some places employ at least an assert(bs->drv); somewhere, that
may be reasonable (such as in the reopen code), but in
bdrv_has_zero_init(), it is definitely not.  Returning 0 there in case
of an ejected BDS saves us much headache instead.

Reported-by: R. Nageswara Sastry <nasastry@in.ibm.com>
Buglink: https://bugs.launchpad.net/qemu/+bug/1728660
Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20171110203111.7666-4-mreitz@redhat.com
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

4 files changed, 59 insertions, 2 deletions

diff --git a/block/io.c b/block/io.c
index 3d5ef2cabe..4fdf93a014 100644
--- a/block/io.c
+++ b/block/io.c
@@ -853,6 +853,10 @@ static int coroutine_fn bdrv_driver_preadv(BlockDriverState *bs,
 
     assert(!(flags & ~BDRV_REQ_MASK));
 
+    if (!drv) {
+        return -ENOMEDIUM;
+    }
+
     if (drv->bdrv_co_preadv) {
         return drv->bdrv_co_preadv(bs, offset, bytes, qiov, flags);
     }
@@ -894,6 +898,10 @@ static int coroutine_fn bdrv_driver_pwritev(BlockDriverState *bs,
 
     assert(!(flags & ~BDRV_REQ_MASK));
 
+    if (!drv) {
+        return -ENOMEDIUM;
+    }
+
     if (drv->bdrv_co_pwritev) {
         ret = drv->bdrv_co_pwritev(bs, offset, bytes, qiov,
                                    flags & bs->supported_write_flags);
@@ -945,6 +953,10 @@ bdrv_driver_pwritev_compressed(BlockDriverState *bs, uint64_t offset,
 {
     BlockDriver *drv = bs->drv;
 
+    if (!drv) {
+        return -ENOMEDIUM;
+    }
+
     if (!drv->bdrv_co_pwritev_compressed) {
         return -ENOTSUP;
     }
@@ -975,6 +987,10 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BdrvChild *child,
                                     BDRV_REQUEST_MAX_BYTES);
     unsigned int progress = 0;
 
+    if (!drv) {
+        return -ENOMEDIUM;
+    }
+
     /* FIXME We cannot require callers to have write permissions when all they
      * are doing is a read request. If we did things right, write permissions
      * would be obtained anyway, but internally by the copy-on-read code. As
@@ -1291,6 +1307,10 @@ static int coroutine_fn bdrv_co_do_pwrite_zeroes(BlockDriverState *bs,
                         bs->bl.request_alignment);
     int max_transfer = MIN_NON_ZERO(bs->bl.max_transfer, MAX_BOUNCE_BUFFER);
 
+    if (!drv) {
+        return -ENOMEDIUM;
+    }
+
     assert(alignment % bs->bl.request_alignment == 0);
     head = offset % alignment;
     tail = (offset + bytes) % alignment;
@@ -1397,6 +1417,10 @@ static int coroutine_fn bdrv_aligned_pwritev(BdrvChild *child,
     uint64_t bytes_remaining = bytes;
     int max_transfer;
 
+    if (!drv) {
+        return -ENOMEDIUM;
+    }
+
     if (bdrv_has_readonly_bitmaps(bs)) {
         return -EPERM;
     }
@@ -1863,6 +1887,8 @@ static int coroutine_fn bdrv_co_block_status(BlockDriverState *bs,
         bytes = n;
     }
 
+    /* Must be non-NULL or bdrv_getlength() would have failed */
+    assert(bs->drv);
     if (!bs->drv->bdrv_co_get_block_status) {
         *pnum = bytes;
         ret = BDRV_BLOCK_DATA | BDRV_BLOCK_ALLOCATED;
@@ -2373,6 +2399,12 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
     }
 
     BLKDBG_EVENT(bs->file, BLKDBG_FLUSH_TO_DISK);
+    if (!bs->drv) {
+        /* bs->drv->bdrv_co_flush() might have ejected the BDS
+         * (even in case of apparent success) */
+        ret = -ENOMEDIUM;
+        goto out;
+    }
     if (bs->drv->bdrv_co_flush_to_disk) {
         ret = bs->drv->bdrv_co_flush_to_disk(bs);
     } else if (bs->drv->bdrv_aio_flush) {
@@ -2542,6 +2574,10 @@ int coroutine_fn bdrv_co_pdiscard(BlockDriverState *bs, int64_t offset,
             num = max_pdiscard;
         }
 
+        if (!bs->drv) {
+            ret = -ENOMEDIUM;
+            goto out;
+        }
         if (bs->drv->bdrv_co_pdiscard) {
             ret = bs->drv->bdrv_co_pdiscard(bs, offset, num);
         } else {
diff --git a/block/qapi.c b/block/qapi.c
index 7fa2437923..fc10f0a565 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -39,8 +39,14 @@ BlockDeviceInfo *bdrv_block_device_info(BlockBackend *blk,
 {
     ImageInfo **p_image_info;
     BlockDriverState *bs0;
-    BlockDeviceInfo *info = g_malloc0(sizeof(*info));
+    BlockDeviceInfo *info;
 
+    if (!bs->drv) {
+        error_setg(errp, "Block device %s is ejected", bs->node_name);
+        return NULL;
+    }
+
+    info = g_malloc0(sizeof(*info));
     info->file                   = g_strdup(bs->filename);
     info->ro                     = bs->read_only;
     info->drv                    = g_strdup(bs->drv->format_name);
diff --git a/block/replication.c b/block/replication.c
index 1c95d673ff..e41e293d2b 100644
--- a/block/replication.c
+++ b/block/replication.c
@@ -342,12 +342,24 @@ static void secondary_do_checkpoint(BDRVReplicationState *s, Error **errp)
         return;
     }
 
+    if (!s->active_disk->bs->drv) {
+        error_setg(errp, "Active disk %s is ejected",
+                   s->active_disk->bs->node_name);
+        return;
+    }
+
     ret = s->active_disk->bs->drv->bdrv_make_empty(s->active_disk->bs);
     if (ret < 0) {
         error_setg(errp, "Cannot make active disk empty");
         return;
     }
 
+    if (!s->hidden_disk->bs->drv) {
+        error_setg(errp, "Hidden disk %s is ejected",
+                   s->hidden_disk->bs->node_name);
+        return;
+    }
+
     ret = s->hidden_disk->bs->drv->bdrv_make_empty(s->hidden_disk->bs);
     if (ret < 0) {
         error_setg(errp, "Cannot make hidden disk empty");
@@ -511,6 +523,9 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
             return;
         }
 
+        /* Must be true, or the bdrv_getlength() calls would have failed */
+        assert(s->active_disk->bs->drv && s->hidden_disk->bs->drv);
+
         if (!s->active_disk->bs->drv->bdrv_make_empty ||
             !s->hidden_disk->bs->drv->bdrv_make_empty) {
             error_setg(errp,
diff --git a/block/vvfat.c b/block/vvfat.c
index 0841cc42fc..a690595f2c 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -2947,7 +2947,7 @@ static int do_commit(BDRVVVFATState* s)
         return ret;
     }
 
-    if (s->qcow->bs->drv->bdrv_make_empty) {
+    if (s->qcow->bs->drv && s->qcow->bs->drv->bdrv_make_empty) {
         s->qcow->bs->drv->bdrv_make_empty(s->qcow->bs);
     }