[PATCH] evm: Fix memleak in init_desc

[Eric Biggers]

On Sat, Jan 09, 2021 at 07:33:05PM +0800, Dinghao Liu wrote:
> When kmalloc() fails, tmp_tfm allocated by
> crypto_alloc_shash() has not been freed, which
> leads to memleak.
> 
> Fixes: d46eb3699502b ("evm: crypto hash replaced by shash")
> Signed-off-by: Dinghao Liu <dinghao.liu at zju.edu.cn>
> ---
>  security/integrity/evm/evm_crypto.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
> index 168c3b78ac47..39fb31a638ac 100644
> --- a/security/integrity/evm/evm_crypto.c
> +++ b/security/integrity/evm/evm_crypto.c
> @@ -73,7 +73,7 @@ static struct shash_desc *init_desc(char type, uint8_t hash_algo)
>  {
>  	long rc;
>  	const char *algo;
> -	struct crypto_shash **tfm, *tmp_tfm;
> +	struct crypto_shash **tfm, *tmp_tfm = NULL;
>  	struct shash_desc *desc;
>  
>  	if (type == EVM_XATTR_HMAC) {
> @@ -118,13 +118,18 @@ static struct shash_desc *init_desc(char type, uint8_t hash_algo)
>  alloc:
>  	desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
>  			GFP_KERNEL);
> -	if (!desc)
> +	if (!desc) {
> +		if (tmp_tfm)
> +			crypto_free_shash(tmp_tfm);
>  		return ERR_PTR(-ENOMEM);
> +	}
>  
>  	desc->tfm = *tfm;
>  
>  	rc = crypto_shash_init(desc);
>  	if (rc) {
> +		if (tmp_tfm)
> +			crypto_free_shash(tmp_tfm);
>  		kfree(desc);
>  		return ERR_PTR(rc);
>  	}

There's no need to check for NULL before calling crypto_free_shash().

- Eric