Am 12.06.2024 um 14:43 hat Amjad Alsharafi geschrieben:
> When reading with `read_cluster` we get the `mapping` with
> `find_mapping_for_cluster` and then we call `open_file` for this
> mapping.
> The issue appear when its the same file, but a second cluster that is
> not immediately after it, imagine clusters `500 -> 503`, this will give
> us 2 mappings one has the range `500..501` and another `503..504`, both
> point to the same file, but different offsets.
>
> When we don't open the file since the path is the same, we won't assign
> `s->current_mapping` and thus accessing way out of bound of the file.
>
> From our example above, after `open_file` (that didn't open anything) we
> will get the offset into the file with
> `s->cluster_size*(cluster_num-s->current_mapping->begin)`, which will
> give us `0x2000 * (504-500)`, which is out of bound for this mapping and
> will produce some issues.
>
> Signed-off-by: Amjad Alsharafi <amjadsharaf...@gmail.com>
> ---
> block/vvfat.c | 23 ++++++++++++++++-------
> 1 file changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/block/vvfat.c b/block/vvfat.c
> index b63ac5d045..fc570d0610 100644
> --- a/block/vvfat.c
> +++ b/block/vvfat.c
> @@ -1360,15 +1360,24 @@ static int open_file(BDRVVVFATState* s,mapping_t*
> mapping)
> {
> if(!mapping)
> return -1;
> + int new_path = 1;
> if(!s->current_mapping ||
> - strcmp(s->current_mapping->path,mapping->path)) {
> - /* open file */
> - int fd = qemu_open_old(mapping->path,
> + s->current_mapping->info.file.offset
> + != mapping->info.file.offset ||
I'm wondering if this couldn't just be s->current_mapping != mapping?
> + (new_path = strcmp(s->current_mapping->path, mapping->path))) {
If both the path and the offset change, we still want to set new_path, I
think. And if we didn't already have a mapping, we also need to open the
file.
Actually, setting a variable inside the condition makes it kind of hard
to read, so if s->current_mapping != mapping works, we can do the check
only in the conditon below:
> + if (new_path) {
if (!s->current_mapping ||
strcmp(s->current_mapping->path, mapping->path))
> + /* open file */
> + int fd = qemu_open_old(mapping->path,
> O_RDONLY | O_BINARY | O_LARGEFILE);
> - if(fd<0)
> - return -1;
> - vvfat_close_current_file(s);
> - s->current_fd = fd;
> + if (fd < 0) {
> + return -1;
> + }
> + vvfat_close_current_file(s);
> +
> + s->current_fd = fd;
> + }
> + assert(s->current_fd);
> s->current_mapping = mapping;
> }
Kevin
