Re: [Qemu-block] [PATCH 1/2] block/vhdx: check error return of bdrv_getlength()

[Jeff Cody]

On Mon, Aug 07, 2017 at 12:46:30PM +0200, Kevin Wolf wrote:
> Am 07.08.2017 um 05:08 hat Jeff Cody geschrieben:
> > Calls to bdrv_getlength() were not checking for error.  In vhdx.c, this
> > can lead to truncating an image file, so it is a definite bug.  In
> > vhdx-log.c, the path for improper behavior is less clear, but it is best
> > to check in any case.
> > 
> > Reported-by: Markus Armbruster <address@hidden>
> > Signed-off-by: Jeff Cody <address@hidden>
> > ---
> >  block/vhdx-log.c | 20 ++++++++++++++++----
> >  block/vhdx.c     |  9 ++++++++-
> >  2 files changed, 24 insertions(+), 5 deletions(-)
> > 
> > diff --git a/block/vhdx-log.c b/block/vhdx-log.c
> > index 01278f3..fd4e7af 100644
> > --- a/block/vhdx-log.c
> > +++ b/block/vhdx-log.c
> > @@ -491,6 +491,7 @@ static int vhdx_log_flush(BlockDriverState *bs, 
> > BDRVVHDXState *s,
> >      uint32_t cnt, sectors_read;
> >      uint64_t new_file_size;
> >      void *data = NULL;
> > +    int64_t file_length;
> >      VHDXLogDescEntries *desc_entries = NULL;
> >      VHDXLogEntryHeader hdr_tmp = { 0 };
> >  
> > @@ -510,10 +511,15 @@ static int vhdx_log_flush(BlockDriverState *bs, 
> > BDRVVHDXState *s,
> >          if (ret < 0) {
> >              goto exit;
> >          }
> > +        file_length = bdrv_getlength(bs->file->bs);
> > +        if (file_length < 0) {
> > +            ret = file_length;
> > +            goto exit;
> > +        }
> >          /* if the log shows a FlushedFileOffset larger than our current 
> > file
> >           * size, then that means the file has been truncated / corrupted, 
> > and
> >           * we must refused to open it / use it */
> > -        if (hdr_tmp.flushed_file_offset > bdrv_getlength(bs->file->bs)) {
> > +        if (hdr_tmp.flushed_file_offset > file_length) {
> >              ret = -EINVAL;
> >              goto exit;
> >          }
> > @@ -543,7 +549,7 @@ static int vhdx_log_flush(BlockDriverState *bs, 
> > BDRVVHDXState *s,
> >                  goto exit;
> >              }
> >          }
> > -        if (bdrv_getlength(bs->file->bs) < 
> > desc_entries->hdr.last_file_offset) {
> > +        if (file_length < desc_entries->hdr.last_file_offset) {
> >              new_file_size = desc_entries->hdr.last_file_offset;
> >              if (new_file_size % (1024*1024)) {
> >                  /* round up to nearest 1MB boundary */
> 
> The vhdx_log_flush() part looks good, but it made me notice a
> bdrv_flush() in the same function where the return value isn't checked.
> I'm almost sure that this is a bug.
> 

I'll add 2 more simple patches to the series: one for bdrv_flush(), and one
for the unchecked bdrv_truncate() as well.


> > @@ -851,6 +857,7 @@ static int vhdx_log_write(BlockDriverState *bs, 
> > BDRVVHDXState *s,
> >      uint32_t partial_sectors = 0;
> >      uint32_t bytes_written = 0;
> >      uint64_t file_offset;
> > +    int64_t file_length;
> >      VHDXHeader *header;
> >      VHDXLogEntryHeader new_hdr;
> >      VHDXLogDescriptor *new_desc = NULL;
> > @@ -913,10 +920,15 @@ static int vhdx_log_write(BlockDriverState *bs, 
> > BDRVVHDXState *s,
> >                  .sequence_number     = s->log.sequence,
> >                  .descriptor_count    = sectors,
> >                  .reserved            = 0,
> > -                .flushed_file_offset = bdrv_getlength(bs->file->bs),
> > -                .last_file_offset    = bdrv_getlength(bs->file->bs),
> >                };
> >  
> > +    file_length = bdrv_getlength(bs->file->bs);
> > +    if (file_length < 0) {
> > +        ret = file_length;
> > +        goto exit;
> > +    }
> > +    new_hdr.flushed_file_offset = file_length;
> > +    new_hdr.last_file_offset    = file_length;
> >      new_hdr.log_guid = header->log_guid;
> 
> If you move the bdrv_getlength() above the initialisation of new_hdr,
> you could keep these fields in the designated initialiser, which should
> be better for readability.
> 
> I also don't know why .log_guid isn't part if it, could be moved, too.
> 
> >      desc_sectors = vhdx_compute_desc_sectors(new_hdr.descriptor_count);
> > diff --git a/block/vhdx.c b/block/vhdx.c
> > index a9cecd2..6a14999 100644
> > --- a/block/vhdx.c
> > +++ b/block/vhdx.c
> > @@ -1166,7 +1166,14 @@ exit:
> >  static int vhdx_allocate_block(BlockDriverState *bs, BDRVVHDXState *s,
> >                                      uint64_t *new_offset)
> >  {
> > -    *new_offset = bdrv_getlength(bs->file->bs);
> > +    int64_t current_len;
> > +    current_len = bdrv_getlength(bs->file->bs);
> > +
> > +    if (current_len < 0) {
> > +        return current_len;
> > +    }
> 
> Don't you want the empty line to be between declaration and code rather
> than assignment and check?
> 
> > +    *new_offset = current_len;
> >  
> >      /* per the spec, the address for a block is in units of 1MB */
> >      *new_offset = ROUND_UP(*new_offset, 1024 * 1024);
> 
> So the code looks correct, but we could make it a little nicer in a v2.
>

Yep, thanks.  I'll address all those cleanups you mentioned in v2.