Re: [PATCH v5 4/5] vvfat: Fix reading files with non-continuous clusters

[Amjad Alsharafi]

On Jul 19 2024, at 8:20 am, Amjad Alsharafi <amjadsharafi10@gmail.com> wrote:

> On Thu, Jul 18, 2024 at 05:20:36PM +0200, Kevin Wolf wrote:
>> 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 <amjadsharafi10@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?
> 
> Actually, you are totally right. Not sure what made me go for this.
> 
> I tried also to test with only checking if the path changed, but it
> fails on some tests. So the offset is important.
> For that reason, checking just the mapping ptr is better since we won't
> have 2 mappings with same file and offset.
> 
> I'll then use this change. Thanks

Should I send a new patch? since most commits are reviewed now

> 
>> 
>> > +            (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
>> 
>