Re: [Qemu-devel] [PATCH v2] crypto_gen_random() now also works on windows

[Daniel P. Berrange]

On Mon, Apr 24, 2017 at 07:51:49PM +0200, Geert Martin Ijewski wrote:
> If no crypto library is included in the build QEMU uses
> qcrypto_random_bytes() to generate random data. That function tried to open
> /dev/urandom or /dev/random and if openeing neither file worked it errored
> out.
> 
> Those files obviously do not exist on windows, so there the code now uses
> CryptGenRandom().
> 
> Furthermore there was some refactoring and a new function
> qcrypto_random_init() was introduced, that initalizes (platform specific)
> handles that are used by qcrypto_random_bytes().
> 
> Signed-off-by: Geert Martin Ijewski <address@hidden>
> ---
>  crypto/init.c            |  6 ++++++
>  crypto/random-platform.c | 45 +++++++++++++++++++++++++++++++++++++--------
>  include/crypto/random.h  |  9 +++++++++
>  3 files changed, 52 insertions(+), 8 deletions(-)
> 
> diff --git a/crypto/init.c b/crypto/init.c
> index f65207e..f131c42
> --- a/crypto/init.c
> +++ b/crypto/init.c
> @@ -32,6 +32,8 @@
>  #include <gcrypt.h>
>  #endif
> 
> +#include "crypto/random.h"
> +
>  /* #define DEBUG_GNUTLS */
> 
>  /*
> @@ -146,5 +148,9 @@ int qcrypto_init(Error **errp)
>      gcry_control(GCRYCTL_INITIALIZATION_FINISHED, 0);
>  #endif
> 
> +    if (qcrypto_random_init(errp) < 0) {
> +        return -1;
> +    }
> +
>      return 0;
>  }
> diff --git a/crypto/random-platform.c b/crypto/random-platform.c
> index 82b755a..49d7f80
> @@ -22,14 +22,23 @@
> 
>  #include "crypto/random.h"
> 
> -int qcrypto_random_bytes(uint8_t *buf G_GNUC_UNUSED,
> -                         size_t buflen G_GNUC_UNUSED,
> -                         Error **errp)
> -{
> -    int fd;
> -    int ret = -1;
> -    int got;
> +#ifdef _WIN32
> +#include <Wincrypt.h>
> +HCRYPTPROV hCryptProv;
> +#else
> +int fd; /* a file handle to either /dev/urandom or /dev/random */
> +#endif


Lets mark both these vars 'static'


> 
> +int qcrypto_random_init(Error **errp)
> +{
> +#ifdef _WIN32
> +    if (!CryptAcquireContext(&hCryptProv, NULL, NULL, PROV_RSA_FULL,
> +                             CRYPT_SILENT | CRYPT_VERIFYCONTEXT)) {
> +        error_setg_errno(errp, GetLastError(),
> +                         "Unable to create cryptographic provider");

Unfortunately the return value of 'GetLastError()' isn't an errno
so we can't use error_setg_errno here.

Just use error_setg, and report the error value with a '(code=%u)'
substitution at the end of the error message.


> +        return -1;
> +    }
> +#else
>      /* TBD perhaps also add support for BSD getentropy / Linux
>       * getrandom syscalls directly */
>      fd = open("/dev/urandom", O_RDONLY);
> @@ -41,6 +50,18 @@ int qcrypto_random_bytes(uint8_t *buf G_GNUC_UNUSED,
>          error_setg(errp, "No /dev/urandom or /dev/random found");
>          return -1;
>      }
> +#endif
> +
> +    return 0;
> +}
> +
> +int qcrypto_random_bytes(uint8_t *buf G_GNUC_UNUSED,
> +                         size_t buflen G_GNUC_UNUSED,
> +                         Error **errp)
> +{
> +#ifndef _WIN32
> +    int ret = -1;
> +    int got;
> 
>      while (buflen > 0) {
>          got = read(fd, buf, buflen);
> @@ -59,6 +80,14 @@ int qcrypto_random_bytes(uint8_t *buf G_GNUC_UNUSED,
> 
>      ret = 0;
>   cleanup:
> -    close(fd);
>      return ret;
> +#else
> +    if (!CryptGenRandom(hCryptProv, buflen, buf)) {
> +        error_setg_errno(errp, GetLastError(),
> +                         "Unable to read random bytes");
> +        return -1;
> +    }
> +
> +    return 0;
> +#endif
>  }
> diff --git a/include/crypto/random.h b/include/crypto/random.h
> index a101353..82a3209
> --- a/include/crypto/random.h
> +++ b/include/crypto/random.h
> @@ -40,5 +40,14 @@ int qcrypto_random_bytes(uint8_t *buf,
>                           size_t buflen,
>                           Error **errp);
> 
> +/**
> + * qcrypto_random_init:
> + * @errp: pointer to a NULL-initialized error object
> + *
> + * Initalizes the handles used by qcrypto_random_bytes
> + *
> + * Returns 0 on success, -1 on error
> + */
> +int qcrypto_random_init(Error **errp);

We need to add a stub

  int qcrypto_random_init(Error **errp G_GNUC_UNUSED) { return 0; }

in the random-gcrypt.c and random-gnutls.c files

Regards,
Daniel
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