[PULL 01/64] block: Raise an error when backing file parameter is an empty string

[Kevin Wolf <kwolf@redhat.com>]

From: Connor Kuehl <ckuehl@redhat.com>

Providing an empty string for the backing file parameter like so:

	qemu-img create -f qcow2 -b '' /tmp/foo

allows the flow of control to reach and subsequently fail an assert
statement because passing an empty string to

	bdrv_get_full_backing_filename_from_filename()

simply results in NULL being returned without an error being raised.

To fix this, let's check for an empty string when getting the value from
the opts list.

Reported-by: Attila Fazekas <afazekas@redhat.com>
Fixes: https://bugzilla.redhat.com/1809553
Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
Message-Id: <20200813134722.802180-1-ckuehl@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block.c                    | 4 ++++
 tests/qemu-iotests/049     | 4 ++++
 tests/qemu-iotests/049.out | 5 +++++
 3 files changed, 13 insertions(+)

diff --git a/block.c b/block.c
index 2ba76b2c36..b204b93a2e 100644
--- a/block.c
+++ b/block.c
@@ -6119,6 +6119,10 @@ void bdrv_img_create(const char *filename, const char *fmt,
                              "same filename as the backing file");
             goto out;
         }
+        if (backing_file[0] == '\0') {
+            error_setg(errp, "Expected backing file name, got empty string");
+            goto out;
+        }
     }
 
     backing_fmt = qemu_opt_get(opts, BLOCK_OPT_BACKING_FMT);
diff --git a/tests/qemu-iotests/049 b/tests/qemu-iotests/049
index 051a1c79e0..82b1e6c202 100755
--- a/tests/qemu-iotests/049
+++ b/tests/qemu-iotests/049
@@ -119,6 +119,10 @@ test_qemu_img create -f $IMGFMT -o compat=1.1,lazy_refcounts=on "$TEST_IMG" 64M
 test_qemu_img create -f $IMGFMT -o compat=0.10,lazy_refcounts=off "$TEST_IMG" 64M
 test_qemu_img create -f $IMGFMT -o compat=0.10,lazy_refcounts=on "$TEST_IMG" 64M
 
+echo "== Expect error when backing file name is empty string =="
+echo
+test_qemu_img create -f $IMGFMT -b '' $TEST_IMG 1M
+
 # success, all done
 echo "*** done"
 rm -f $seq.full
diff --git a/tests/qemu-iotests/049.out b/tests/qemu-iotests/049.out
index a7e220830d..b1d8fd9107 100644
--- a/tests/qemu-iotests/049.out
+++ b/tests/qemu-iotests/049.out
@@ -209,4 +209,9 @@ qemu-img create -f qcow2 -o compat=0.10,lazy_refcounts=on TEST_DIR/t.qcow2 64M
 Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 cluster_size=65536 extended_l2=off compression_type=zlib size=67108864 compat=0.10 lazy_refcounts=on refcount_bits=16
 qemu-img: TEST_DIR/t.qcow2: Lazy refcounts only supported with compatibility level 1.1 and above (use version=v3 or greater)
 
+== Expect error when backing file name is empty string ==
+
+qemu-img create -f qcow2 -b  TEST_DIR/t.qcow2 1M
+qemu-img: TEST_DIR/t.qcow2: Expected backing file name, got empty string
+
 *** done
-- 
2.25.4