Re: [PATCH] vsprintf: Make sure argument to %*ph/%pv is valid

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 02/10/2015 04:49 PM, Andrew Cooper wrote:
> On 10/02/2015 21:44, Boris Ostrovsky wrote:
>> If NULL pointer is passed for these specifiers then print '-'
>> or 'd-v-'.
>>
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Instead of special casing each custom format, I would be tempted just to
> put the switch() in an if(arg) conditional, and fall back to the regular
> number for a NULL pointer, or go along the glibc route and print "(NULL)".

OK, I could do that.

>
> I presume you found this by falling over a NULL  pointer while
> debugging?  I can't see a legitimate reason for formally supporting NULL
> pointers in each context, but crashing is certainly better avoided.

Yes, I hit %pv case when the vcpu I was tracking turned NULL. And yes, 
we then crash.

-boris

>
> ~Andrew
>
>> ---
>>   xen/common/vsprintf.c |   19 +++++++++++++++++++
>>   1 files changed, 19 insertions(+), 0 deletions(-)
>>
>> diff --git a/xen/common/vsprintf.c b/xen/common/vsprintf.c
>> index 065cc42..84cfa85 100644
>> --- a/xen/common/vsprintf.c
>> +++ b/xen/common/vsprintf.c
>> @@ -280,6 +280,13 @@ static char *pointer(char *str, char *end, const char **fmt_ptr,
>>           /* Consumed 'h' from the format string. */
>>           ++*fmt_ptr;
>>   
>> +        if ( hex_buffer == NULL )
>> +        {
>> +            if ( str < end )
>> +                *str++ = '-';
>> +            return str;
>> +        }
>> +
>>           /* Bound user count from %* to between 0 and 64 bytes. */
>>           if ( field_width <= 0 )
>>               return str;
>> @@ -338,6 +345,18 @@ static char *pointer(char *str, char *end, const char **fmt_ptr,
>>           ++*fmt_ptr;
>>           if ( str < end )
>>               *str = 'd';
>> +        if ( v == NULL )
>> +        {
>> +            /* If v is NULL then print 'd-v-' */
>> +            str++;
>> +            if ( str < end )
>> +                *str++ = '-';
>> +            if ( str < end )
>> +                *str++ = 'v';
>> +            if ( str < end )
>> +                *str++ = '-';
>> +            return str;
>> +        }
>>           str = number(str + 1, end, v->domain->domain_id, 10, -1, -1, 0);
>>           if ( str < end )
>>               *str = 'v';