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

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

On 5/22/22 05:00, Sergey Shtylyov wrote:
> 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?

It was the kernel 0-day build bot for non-x86 arch, can't remember which one.

> 
>> 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


-- 
Damien Le Moal
Western Digital Research