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ext2simg: Fix off-by-one errors causing corruption #116

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ext2simg: Fix off-by-one errors causing corruption #116

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17 changes: 14 additions & 3 deletions contrib/android/ext2simg.c
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Original file line number Diff line number Diff line change
Expand Up @@ -63,6 +63,9 @@ static struct buf_item {
void *buf[0];
} *buf_list;

/* Add the blocks [chunk_start, chunk_end) in the filesystem specificed by fs
* to the sparse file s. Note that the block at chunk_end is NOT included in
* the output. */
static void add_chunk(ext2_filsys fs, struct sparse_file *s, blk_t chunk_start, blk_t chunk_end)
{
int retval;
Expand Down Expand Up @@ -146,16 +149,24 @@ static struct sparse_file *ext_to_sparse(const char *in_file)
if (chunk_start == -1) {
chunk_start = cur_blk;
} else if (cur_blk - chunk_start + 1 == max_blk_per_chunk) {
add_chunk(fs, s, chunk_start, cur_blk);
/* cur_blk is used, so we must add [chunk_start, cur_blk], i.e.
* pass cur_blk + 1 here. */
add_chunk(fs, s, chunk_start, cur_blk + 1);
chunk_start = -1;
}
} else if (chunk_start != -1) {
/* cur_blk is unused, so add [chunk_start, cur_blk) */
add_chunk(fs, s, chunk_start, cur_blk);
chunk_start = -1;
}
}
if (chunk_start != -1)
add_chunk(fs, s, chunk_start, cur_blk - 1);
if (chunk_start != -1) {
/* (cur_blk - 1) must be used, otherwise the code for unused blocks
* above would have processed this. We must include the block, but the
* upper boundary for add_chunk is exclusive, so to add [chunk_start,
* cur_blk - 1] to the sparse image, pass cur_blk. */
add_chunk(fs, s, chunk_start, cur_blk);
}

ext2fs_free(fs);
return s;
Expand Down