[Qemu-devel] [PATCH 08/10] block/dmg: fix sector data offset calculation

[Peter Wu <peter@lekensteyn.nl>]

This patch addresses two issues:

 - The data fork offset was not taken into account, resulting in failure
   to read an InstallESD.dmg file (5164763151 bytes) which had a
   non-zero DataForkOffset field.
 - The offset of the previous block ("partition") was unconditionally
   added to the current block because older files would start the input
   offset of a new block at zero. Newer files (including vlc-2.1.5.dmg,
   tuxpaint-0.9.15-macosx.dmg and OS X Yosemite [MAS].dmg) failed in
   reads because these files have a continuous input offset.

Signed-off-by: Peter Wu <peter@lekensteyn.nl>
---
 block/dmg.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/block/dmg.c b/block/dmg.c
index 984997f..93b597f 100644
--- a/block/dmg.c
+++ b/block/dmg.c
@@ -179,6 +179,7 @@ static int64_t dmg_find_koly_offset(BlockDriverState *file_bs)
 typedef struct DmgHeaderState {
     /* used internally by dmg_read_mish_block to remember offsets of blocks
      * across calls */
+    uint64_t data_fork_offset;
     uint64_t last_in_offset;
     uint64_t last_out_offset;
     /* exported for dmg_open */
@@ -194,6 +195,7 @@ static int dmg_read_mish_block(BDRVDMGState *s, DmgHeaderState *ds,
     size_t new_size;
     uint32_t chunk_count;
     int64_t offset = 0;
+    uint64_t in_offset = ds->data_fork_offset;
 
     type = buff_read_uint32(buffer, offset);
     /* skip data that is not a valid MISH block (invalid magic or too small) */
@@ -246,7 +248,12 @@ static int dmg_read_mish_block(BDRVDMGState *s, DmgHeaderState *ds,
         }
 
         s->offsets[i] = buff_read_uint64(buffer, offset);
-        s->offsets[i] += ds->last_in_offset;
+        /* If this offset is below the previous chunk end, then assume that all
+         * following offsets are after the previous chunks. */
+        if (s->offsets[i] + in_offset < ds->last_in_offset) {
+            in_offset = ds->last_in_offset;
+        }
+        s->offsets[i] += in_offset;
         offset += 8;
 
         s->lengths[i] = buff_read_uint64(buffer, offset);
@@ -400,6 +407,7 @@ static int dmg_open(BlockDriverState *bs, QDict *options, int flags,
     bs->read_only = 1;
     s->n_chunks = 0;
     s->offsets = s->lengths = s->sectors = s->sectorcounts = NULL;
+    ds.data_fork_offset = 0;
     ds.last_in_offset = 0;
     ds.last_out_offset = 0;
     ds.max_compressed_size = 1;
@@ -412,6 +420,12 @@ static int dmg_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
+    /* offset of data fork (DataForkOffset) */
+    ret = read_uint64(bs, offset + 0x18, &ds.data_fork_offset);
+    if (ret < 0) {
+        goto fail;
+    }
+
     /* offset of resource fork (RsrcForkOffset) */
     ret = read_uint64(bs, offset + 0x28, &rsrc_fork_offset);
     if (ret < 0) {
-- 
2.2.1