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

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Date:   Wed, 13 Jan 2021 06:51:49 -0600
From:   Steve Magnani <magnani@...e.org>
To:     lianzhi chang <changlianzhi@...ontech.com>
Cc:     jack@...e.com, linux-kernel@...r.kernel.org, 282827961@...com
Subject: Re: [PATCH] udf: fix the problem that the disc content is not
 displayed

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
> logic, 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@...ontech.com>
> ---
>  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@...e.org>
------------------------------------------------------------------------
  Steven J. Magnani               "I claim this network for MARS!
                                   Earthling, return my space modulator!"

  #include <standard.disclaimer>