Re: [Qemu-devel] [PATCH] cipher: fix leak on initialization error

[Daniel P. Berrange]

On Wed, Nov 09, 2016 at 02:18:15PM +0400, Marc-André Lureau wrote:
> If ctx->blocksize != XTS_BLOCK_SIZE, ctx will be leaked.
> Assign ctx earler, and call qcrypto_cipher_free() on error.
> 
> Spotted thanks to ASAN.
> 
> Signed-off-by: Marc-André Lureau <address@hidden>
> ---
>  crypto/cipher-nettle.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/crypto/cipher-nettle.c b/crypto/cipher-nettle.c
> index cd094cd..593962c 100644
> --- a/crypto/cipher-nettle.c
> +++ b/crypto/cipher-nettle.c
> @@ -376,6 +376,7 @@ QCryptoCipher *qcrypto_cipher_new(QCryptoCipherAlgorithm 
> alg,
>          goto error;
>      }

'ctx' is non-NULL at this point and there's a 'goto error' just
above here....

>  
> +    cipher->opaque = ctx;
>      if (mode == QCRYPTO_CIPHER_MODE_XTS &&
>          ctx->blocksize != XTS_BLOCK_SIZE) {
>          error_setg(errp, "Cipher block size %zu must equal XTS block size 
> %d",
> @@ -384,13 +385,11 @@ QCryptoCipher 
> *qcrypto_cipher_new(QCryptoCipherAlgorithm alg,
>      }
>  
>      ctx->iv = g_new0(uint8_t, ctx->blocksize);
> -    cipher->opaque = ctx;
>  
>      return cipher;
>  
>   error:
> -    g_free(cipher);
> -    g_free(ctx);
> +    qcrypto_cipher_free(cipher);
>      return NULL;
>  }


...so you're leaking 'ctx' now, since it hasn't been assigned
to cipher->ctx.

You need to move 'cipher->opque = ctx' to the place where we
initially allocate 'ctx', before any gotos at which point....

>  
> @@ -404,10 +403,12 @@ void qcrypto_cipher_free(QCryptoCipher *cipher)
>      }
>  
>      ctx = cipher->opaque;
> -    g_free(ctx->iv);
> -    g_free(ctx->ctx);
> -    g_free(ctx->ctx_tweak);
> -    g_free(ctx);
> +    if (ctx) {
> +        g_free(ctx->iv);
> +        g_free(ctx->ctx);
> +        g_free(ctx->ctx_tweak);
> +        g_free(ctx);
> +    }
>      g_free(cipher);
>  }

...this change is not needed

Regards,
Daniel
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