[Qemu-devel] [PULL 5/5] block/vdi: Limit maximum size even futher

[Kevin Wolf]

From: Max Reitz <address@hidden>

The block layer read and write functions do not like requests which are
bigger than INT_MAX bytes. Since the VDI bmap is read and written in a
single operation, its size is therefore limited accordingly. This
reduces the maximum VDI image size supported by QEMU to half of what it
currently is (down to approximately 512 TB).

The VDI test 084 has to be adapted accordingly. Actually, one could
clearly see that it was broken from the "Could not open
'TEST_DIR/t.IMGFMT': Invalid argument" line for an image which was
supposed to work just fine.

Signed-off-by: Max Reitz <address@hidden>
Reviewed-by: Stefan Hajnoczi <address@hidden>
Reviewed-by: Peter Lieven <address@hidden>
---
 block/vdi.c                | 14 ++++++++++++--
 tests/qemu-iotests/084     | 14 +++++++-------
 tests/qemu-iotests/084.out | 13 ++++++++-----
 3 files changed, 27 insertions(+), 14 deletions(-)

diff --git a/block/vdi.c b/block/vdi.c
index e1d211c..39070b7 100644
--- a/block/vdi.c
+++ b/block/vdi.c
@@ -120,8 +120,18 @@ typedef unsigned char uuid_t[16];
 
 #define VDI_IS_ALLOCATED(X) ((X) < VDI_DISCARDED)
 
-/* max blocks in image is (0xffffffff / 4) */
-#define VDI_BLOCKS_IN_IMAGE_MAX  0x3fffffff
+/* The bmap will take up VDI_BLOCKS_IN_IMAGE_MAX * sizeof(uint32_t) bytes; 
since
+ * the bmap is read and written in a single operation, its size needs to be
+ * limited to INT_MAX; furthermore, when opening an image, the bmap size is
+ * rounded up to be aligned on BDRV_SECTOR_SIZE.
+ * Therefore this should satisfy the following:
+ * VDI_BLOCKS_IN_IMAGE_MAX * sizeof(uint32_t) + BDRV_SECTOR_SIZE == INT_MAX + 1
+ * (INT_MAX + 1 is the first value not representable as an int)
+ * This guarantees that any value below or equal to the constant will, when
+ * multiplied by sizeof(uint32_t) and rounded up to a BDRV_SECTOR_SIZE 
boundary,
+ * still be below or equal to INT_MAX. */
+#define VDI_BLOCKS_IN_IMAGE_MAX \
+    ((unsigned)((INT_MAX + 1u - BDRV_SECTOR_SIZE) / sizeof(uint32_t)))
 #define VDI_DISK_SIZE_MAX        ((uint64_t)VDI_BLOCKS_IN_IMAGE_MAX * \
                                   (uint64_t)DEFAULT_CLUSTER_SIZE)
 
diff --git a/tests/qemu-iotests/084 b/tests/qemu-iotests/084
index 2712c02..733018d 100755
--- a/tests/qemu-iotests/084
+++ b/tests/qemu-iotests/084
@@ -66,15 +66,15 @@ stat -c"disk image file size in bytes: %s" "${TEST_IMG}"
 
 # check for image size too large
 # poke max image size, and appropriate blocks_in_image value
-echo "Test 1: Maximum size (1024 TB):"
-poke_file "$TEST_IMG" "$ds_offset" "\x00\x00\xf0\xff\xff\xff\x03\x00"
-poke_file "$TEST_IMG" "$bii_offset" "\xff\xff\xff\x3f"
+echo "Test 1: Maximum size (512 TB - 128 MB):"
+poke_file "$TEST_IMG" "$ds_offset" "\x00\x00\x00\xf8\xff\xff\x01\x00"
+poke_file "$TEST_IMG" "$bii_offset" "\x80\xff\xff\x1f"
 _img_info
 
 echo
-echo "Test 2: Size too large (1024TB + 1)"
+echo "Test 2: Size too large (512 TB - 128 MB + 64 kB)"
 # This should be too large (-EINVAL):
-poke_file "$TEST_IMG" "$ds_offset" "\x00\x00\xf1\xff\xff\xff\x03\x00"
+poke_file "$TEST_IMG" "$ds_offset" "\x00\x00\x01\xf8\xff\xff\x01\x00"
 _img_info
 
 echo
@@ -89,9 +89,9 @@ _img_info
 
 echo
 echo "Test 4: Size valid (64M), but Blocks In Image exceeds max allowed"
-# Now check the bounds of blocks_in_image - 0x3fffffff should be the max
+# Now check the bounds of blocks_in_image - 0x1fffff80 should be the max
 # value here, and we should get -ENOTSUP
-poke_file "$TEST_IMG" "$bii_offset" "\x00\x00\x00\x40"
+poke_file "$TEST_IMG" "$bii_offset" "\x81\xff\xff\x1f"
 _img_info
 
 # Finally, 1MB is the only block size supported.  Verify that
diff --git a/tests/qemu-iotests/084.out b/tests/qemu-iotests/084.out
index ea29ae0..5ece829 100644
--- a/tests/qemu-iotests/084.out
+++ b/tests/qemu-iotests/084.out
@@ -17,17 +17,20 @@ file format: IMGFMT
 virtual size: 64M (67108864 bytes)
 cluster_size: 1048576
 disk image file size in bytes: 1024
-Test 1: Maximum size (1024 TB):
-qemu-img: Could not open 'TEST_DIR/t.IMGFMT': Could not open 
'TEST_DIR/t.IMGFMT': Invalid argument
+Test 1: Maximum size (512 TB - 128 MB):
+image: TEST_DIR/t.IMGFMT
+file format: IMGFMT
+virtual size: 512T (562949819203584 bytes)
+cluster_size: 1048576
 
-Test 2: Size too large (1024TB + 1)
-qemu-img: Could not open 'TEST_DIR/t.IMGFMT': Unsupported VDI image size (size 
is 0x3fffffff10000, max supported is 0x3fffffff00000)
+Test 2: Size too large (512 TB - 128 MB + 64 kB)
+qemu-img: Could not open 'TEST_DIR/t.IMGFMT': Unsupported VDI image size (size 
is 0x1fffff8010000, max supported is 0x1fffff8000000)
 
 Test 3: Size valid (64M), but Blocks In Image too small (63)
 qemu-img: Could not open 'TEST_DIR/t.IMGFMT': unsupported VDI image (disk size 
67108864, image bitmap has room for 66060288)
 
 Test 4: Size valid (64M), but Blocks In Image exceeds max allowed
-qemu-img: Could not open 'TEST_DIR/t.IMGFMT': unsupported VDI image (too many 
blocks 1073741824, max is 1073741823)
+qemu-img: Could not open 'TEST_DIR/t.IMGFMT': unsupported VDI image (too many 
blocks 536870785, max is 536870784)
 
 Test 5: Valid Image: 64MB, Blocks In Image 64, Block Size 1MB
 image: TEST_DIR/t.IMGFMT
-- 
1.8.3.1