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

[Daniel P . Berrangé]

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.

Regards,
Daniel
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