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SubjectRe: [PATCH] x86/power/64: Remove VLA usage
On Sun, Jul 15, 2018 at 08:56:57PM -0700, Kees Cook wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> removes the discouraged use of AHASH_REQUEST_ON_STACK by switching to
> shash directly and allocating the descriptor in heap memory (which should
> be fine: the tfm has already been allocated there too).
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> arch/x86/power/hibernate_64.c | 35 +++++++++++++++++++----------------
> 1 file changed, 19 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/power/hibernate_64.c b/arch/x86/power/hibernate_64.c
> index 67ccf64c8bd8..0ed01bb935a6 100644
> --- a/arch/x86/power/hibernate_64.c
> +++ b/arch/x86/power/hibernate_64.c
> @@ -233,28 +233,31 @@ struct restore_data_record {
> */
> static int get_e820_md5(struct e820_table *table, void *buf)
> {
> - struct scatterlist sg;
> - struct crypto_ahash *tfm;
> + struct crypto_shash *tfm;
> + struct shash_desc *desc;
> int size;
> int ret = 0;
>
> - tfm = crypto_alloc_ahash("md5", 0, CRYPTO_ALG_ASYNC);
> + tfm = crypto_alloc_shash("md5", 0, 0);
> if (IS_ERR(tfm))
> return -ENOMEM;
>
> - {
> - AHASH_REQUEST_ON_STACK(req, tfm);
> - size = offsetof(struct e820_table, entries) + sizeof(struct e820_entry) * table->nr_entries;
> - ahash_request_set_tfm(req, tfm);
> - sg_init_one(&sg, (u8 *)table, size);
> - ahash_request_set_callback(req, 0, NULL, NULL);
> - ahash_request_set_crypt(req, &sg, buf, size);
> -
> - if (crypto_ahash_digest(req))
> - ret = -EINVAL;
> - ahash_request_zero(req);
> - }
> - crypto_free_ahash(tfm);
> + desc = kmalloc(sizeof(struct shash_desc) + crypto_shash_descsize(tfm),
> + GFP_KERNEL);
> + if (!desc)
> + return -ENOMEM;

Need crypto_free_shash(tfm) if the kmalloc() here fails.

> +
> + desc->tfm = tfm;
> + desc->flags = 0;
> +
> + size = offsetof(struct e820_table, entries) +
> + sizeof(struct e820_entry) * table->nr_entries;
> +
> + if (crypto_shash_digest(desc, (u8 *)table, size, buf))
> + ret = -EINVAL;
> +
> + kzfree(desc);
> + crypto_free_shash(tfm);
>
> return ret;
> }
> --
> 2.17.1
>
>
> --
> Kees Cook
> Pixel Security

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