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

[Kevin Wolf]

Am 19.07.2024 um 02:29 hat Amjad Alsharafi geschrieben:
> 
> 
> 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

Yes, please do. I think I reviewed the whole series.

Kevin

> > 
> >> 
> >> > +            (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
> >> 
> > 
>