Re: [Qemu-devel] [PATCH v2 07/14] ui/vnc: Use qcrypto_random_bytes for make_challenge

[Philippe Mathieu-Daudé]

On 3/14/19 4:39 PM, Daniel P. Berrangé wrote:
> On Wed, Mar 13, 2019 at 09:55:19PM -0700, Richard Henderson wrote:
>> Use a better interface for random numbers than rand,
>> plus some useless floating point arithmetic.
>>
>> Cc: Gerd Hoffmann <address@hidden>
>> Signed-off-by: Richard Henderson <address@hidden>
>> ---
>> v2: Use qcrypto_random_bytes, not qemu_getrandom, as there is
>>     no need for deterministic results for this interface.
>> ---
>>  ui/vnc.c | 8 ++------
>>  1 file changed, 2 insertions(+), 6 deletions(-)
>>
>> diff --git a/ui/vnc.c b/ui/vnc.c
>> index 1871422e1d..9fa586dfa0 100644
>> --- a/ui/vnc.c
>> +++ b/ui/vnc.c
>> @@ -43,6 +43,7 @@
>>  #include "crypto/hash.h"
>>  #include "crypto/tlscredsanon.h"
>>  #include "crypto/tlscredsx509.h"
>> +#include "crypto/random.h"
>>  #include "qom/object_interfaces.h"
>>  #include "qemu/cutils.h"
>>  #include "io/dns-resolver.h"
>> @@ -2537,12 +2538,7 @@ void start_client_init(VncState *vs)
>>  
>>  static void make_challenge(VncState *vs)
>>  {
>> -    int i;
>> -
>> -    srand(time(NULL)+getpid()+getpid()*987654+rand());
>> -
>> -    for (i = 0 ; i < sizeof(vs->challenge) ; i++)
>> -        vs->challenge[i] = (int) (256.0*rand()/(RAND_MAX+1.0));
>> +    qcrypto_random_bytes(vs->challenge, sizeof(vs->challenge), 
>> &error_fatal);
>>  }
> 
> Old code would not fail, but the new code can. So make_challenge needs
> to return an error to the caller, which must then drop the client conn.

Is the old code equivalent to using a NULL errp?

  qcrypto_random_bytes(vs->challenge, sizeof(vs->challenge), NULL);

> 
> Regards,
> Daniel
>