[Qemu-devel] [PATCH v3] vmdk: return ERROR when cluster sector is larger than vmdk limitation

[Qemu-devel] [PATCH v3] vmdk: return ERROR when cluster sector is larger than vmdk limitation

[yuchenlin]

From: yuchenlin <yuchenlin@synology.com>

VMDK has a hard limitation of extent size, which is due to the size of grain
table entry is 32 bits. It means it can only point to a grain located at
offset = 2^32. To avoid writing the user data beyond limitation and record a useless offset
in grain table. We should return ERROR here.

Signed-off-by: yuchenlin <yuchenlin@synology.com>
---
v2->v3:
 - use (1ULL << 32) to clearly show the limitation of offset is 2^32.

 thanks

 block/vmdk.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/block/vmdk.c b/block/vmdk.c
index f94c49a9c0..84f8bbe480 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -47,6 +47,8 @@
 #define VMDK4_FLAG_MARKER (1 << 17)
 #define VMDK4_GD_AT_END 0xffffffffffffffffULL
 
+#define VMDK_EXTENT_MAX_SECTORS (1ULL << 32)
+
 #define VMDK_GTE_ZEROED 0x1
 
 /* VMDK internal error codes */
@@ -1250,6 +1252,10 @@ static int get_cluster_offset(BlockDriverState *bs,
             return zeroed ? VMDK_ZEROED : VMDK_UNALLOC;
         }
 
+        if (extent->next_cluster_sector >= VMDK_EXTENT_MAX_SECTORS) {
+            return VMDK_ERROR;
+        }
+
         cluster_sector = extent->next_cluster_sector;
         extent->next_cluster_sector += extent->cluster_sectors;
 
-- 
2.16.2

Re: [Qemu-devel] [PATCH v3] vmdk: return ERROR when cluster sector is larger than vmdk limitation

[Max Reitz]

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On 2018-03-22 14:33, yuchenlin@synology.com wrote:
> From: yuchenlin <yuchenlin@synology.com>
> 
> VMDK has a hard limitation of extent size, which is due to the size of grain
> table entry is 32 bits. It means it can only point to a grain located at
> offset = 2^32. To avoid writing the user data beyond limitation and record a useless offset
> in grain table. We should return ERROR here.
> 
> Signed-off-by: yuchenlin <yuchenlin@synology.com>
> ---
> v2->v3:
>  - use (1ULL << 32) to clearly show the limitation of offset is 2^32.
> 
>  thanks
> 
>  block/vmdk.c | 6 ++++++
>  1 file changed, 6 insertions(+)

Thanks, applied to my block branch:

https://github.com/XanClic/qemu/commits/block

Max


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