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Re: [Qemu-block] [Qemu-devel] [PATCH v2] vmdk: return ERROR when cluster

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v2] vmdk: return ERROR when cluster sector is larger than vmdk limitation
Date: Thu, 22 Mar 2018 08:07:07 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0

On 03/22/2018 02:41 AM, Fam Zheng wrote:
On Thu, 03/22 14:24, address@hidden wrote:
From: yuchenlin <address@hidden>

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 <address@hidden>

+++ 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 (4294967296)

Hmm, with sectors instead of bytes, you don't want to use Phillipe's '2 * T_BYTE' macro after all; but it would still look better spelled as '(1ULL << 32)' or '(4ULL * 1024 * 1024 * 1024)'. Most importantly, since the value does NOT fit in a 32-bit unsigned integer, I think you NEED to use the ULL suffix to make your intent clear.

  #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;

Cc'ing Kevin and Max who merge block/ patches.

Also, CC'ing qemu-block, as all block-related patches should go through there.

Reviewed-by: Fam Zheng <address@hidden>

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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