Re: [PATCH 1/3] pc-bios/s390-ccw: fix off-by-one error

[Marc Hartmayer <mhartmay@linux.ibm.com>]

On Thu, Sep 24, 2020 at 12:02 PM +0200, Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
> Hi Marc,
>
> On 9/24/20 10:59 AM, Marc Hartmayer wrote:
>> This error takes effect when the magic value "zIPL" is located at the
>> end of a block. For example if s2_cur_blk = 0x7fe18000 and the magic
>> value "zIPL" is located at 0x7fe18ffc - 0x7fe18fff.
>> 
>> Fixes: ba831b25262a ("s390-ccw: read stage2 boot loader data to find menu")
>> Reviewed-by: Collin Walling <walling@linux.ibm.com>
>> Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
>> ---
>>  pc-bios/s390-ccw/bootmap.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/pc-bios/s390-ccw/bootmap.c b/pc-bios/s390-ccw/bootmap.c
>> index 97205674e59a..0d29dceaa3cc 100644
>> --- a/pc-bios/s390-ccw/bootmap.c
>> +++ b/pc-bios/s390-ccw/bootmap.c
>> @@ -163,7 +163,7 @@ static bool find_zipl_boot_menu_banner(int *offset)
>>      int i;
>>  
>>      /* Menu banner starts with "zIPL" */
>> -    for (i = 0; i < virtio_get_block_size() - 4; i++) {
>> +    for (i = 0; i < virtio_get_block_size() - 3; i++) {
>
> Easier to review as:
>
>        for (i = 0; i <= virtio_get_block_size() - 4; i++) {

Yep.

>
> Even easier defining ZIPL_MAGIC_SIZE instead of the magic '4'.

I thought about adding such a macro as well. Makes even more sense with
your proposed change.

>
>>          if (magic_match(s2_cur_blk + i, ZIPL_MAGIC_EBCDIC)) {
>>              *offset = i;
>>              return true;
>> 
>
-- 
Kind regards / Beste Grüße
   Marc Hartmayer

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