Re: [PATCH] ata: libata-core: fix NULL pointer deref in ata_host_alloc_pinfo()

[Sergey Shtylyov <s.shtylyov@omp.ru>]

Hello!

On 5/21/22 2:45 AM, Damien Le Moal wrote:

>> In an unlikely (and probably wrong?) case that the 'ppi' parameter of
>> ata_host_alloc_pinfo() points to an array starting with a NULL pointer,
>> there's going to be a kernel oops as the 'pi' local variable won't get
>> reassigned from the initial value of NULL.  Assign &ata_dummy_port_info
>> to 'pi' at the start of the *for* loop instead to fix this kernel oops
>> for good...
>>
>> Found by Linux Verification Center (linuxtesting.org) with the SVACE static
>> analysis tool.
>>
>> Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
>>
>> ---
>> This patch is against the 'for-next' branch of Damien's 'libata.git' repo.
>>
>>  drivers/ata/libata-core.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> Index: libata/drivers/ata/libata-core.c
>> ===================================================================
>> --- libata.orig/drivers/ata/libata-core.c
>> +++ libata/drivers/ata/libata-core.c
>> @@ -5470,7 +5470,7 @@ struct ata_host *ata_host_alloc_pinfo(st
>>  	if (!host)
>>  		return NULL;
>>  
>> -	for (i = 0, j = 0, pi = NULL; i < host->n_ports; i++) {
>> +	for (i = 0, j = 0, pi = &ata_dummy_port_info; i < host->n_ports; i++) {
>>  		struct ata_port *ap = host->ports[i];
>>  
>>  		if (ppi[j])
> 
> I had a fight with this one a while back as the build bot was complaining
> about this a while back.

   Hm, what exact tool was complaining?

> pi cannot be null in this case, but silencing
> warnings is good. So OK.

   At least it shouldn't be NULL with a tested driver... I found one driver (pata_cs5520)
that sets the port info array entries to &ata_dummy_port_info on disabled ports, hence
was my idea to also use it...

> Just one nit: please move the initialization of pi to its declaration to
> avoid the overly long for line.

   It's not _overly_ long but OK. :-)

MBR, Sergey