Re: [PATCH] udf: fix the problem that the disc content is not displayed

[Steve Magnani]

On 2021-01-13 20:51, 常廉志 wrote:

> On 2021-01-11 23:53, lianzhi chang wrote:
>
> > > When the capacity of the disc is too large (assuming the 4.7G
> > > specification), the disc (UDF file system) will be burned
> > > multiple times in the windows (Multisession Usage). When the
> > > remaining capacity of the CD is less than 300M (estimated
> > > value, for reference only), open the CD in the Linux system,
> > > the content of the CD is displayed as blank (the kernel will
> > > say "No VRS found"). Windows can display the contents of the
> > > CD normally.
> > > Through analysis, in the "fs/udf/super.c": udf_check_vsd
> > > function, the actual value of VSD_MAX_SECTOR_OFFSET may
> > > be much larger than 0x800000. According to the current code
> > l>ogic, it is found that the type of sbi->s_session is "__s32",
> > > when the remaining capacity of the disc is less than 300M
> > > (take a set of test values: sector=3154903040,
> > > sbi->s_session=1540464, sb->s_blocksize_bits=11 ), the
> > > calculation result of "sbi->s_session << sb->s_blocksize_bits"
> > > will overflow. Therefore, it is necessary to convert the
> > > type of s_session to "loff_t" (when udf_check_vsd starts,
> > > assign a value to _sector, which is also converted in this
> > > way), so that the result will not overflow, and then the
> > > content of the disc can be displayed normally.
> > >
> > > Signed-off-by: lianzhi chang <changlianzhi@xxxxxxxxxxxxx>
> > > ---
> > > fs/udf/super.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/fs/udf/super.c b/fs/udf/super.c
> > > index 5bef3a68395d..6c3069cd1321 100644
> > > --- a/fs/udf/super.c
> > > +++ b/fs/udf/super.c
> > > @@ -757,7 +757,7 @@ static int udf_check_vsd(struct super_block *sb)
> > >
> > > if (nsr > 0)
> > > return 1;
> > > - else if (!bh && sector - (sbi->s_session << sb->s_blocksize_bits) 
> > > ==
> > > + else if (!bh && sector - ((loff_t)sbi->s_session <<
> > > sb->s_blocksize_bits) ==
> > > VSD_FIRST_SECTOR_OFFSET)
> > > return -1;
> > > else
> >
> >
> > Looks good. Perhaps consider factoring out the conversion (which also
> > occurs
> > earlier in the function) so that the complexity of this "else if" can 
> > be
> > reduced?
>
> > Reviewed-by: Steven J. Magnani <magnani@xxxxxxxx>
>
> Thank you very much! So, which one of the following methods do you 
> think is better:
>
> (1) Change the type of s_session in struct udf_sb_info to __s64. If you 
> modify this way, it may involve some memory copy problems of the 
> structure, and there are more modifications.
>
> (2) Definition: loff_t sector_offset=sbi->s_session << 
> sb->s_blocksize_bits, and then put sector_offset into the "else if" 
> statement.
>
> (3) Or is there any other better way?

I had #2 in mind.
------------------------------------------------------------------------
 Steven J. Magnani               "I claim this network for MARS!
                                  Earthling, return my space modulator!"
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