[PATCH v2] Add optional salt to AUTOBOOT_STOP_STR_SHA256

[Joel Peshkin]

Hi Heinrich,

   Thank you for the review.   I increased the max size to 64 characters.
 The size, in the end, is the size of the salt plus the size of the
password the human user would type.   In most places I have seen salt used,
it is only a few characters (modern Linux password databases use 8) and the
actual password (as opposed to its sha256) is unlikely to be more than 15
characters.

Regards,

Joel


On Fri, Nov 20, 2020 at 10:05 AM Joel Peshkin <joel.peshkin at broadcom.com>
wrote:

> From: Joel Peshkin <joel.peshkin at broadcom.com>
>
> Adds an optional SALT value to AUTOBOOT_STOP_STR_SHA256.   If a string
> followed by a ":" is prepended to the sha256, the portion to the left
> of the colon will be used as a salt and the password will be appended
> to the salt before the sha256 is computed and compared.
>
> Signed-off-by: Joel Peshkin <joel.peshkin at broadcom.com>
> Cc: Simon Glass <sjg at chromium.org>
> Cc: Bin Meng <bmeng.cn at gmail.com>
> Cc: Patrick Delaunay <patrick.delaunay at st.com>
> Cc: Heiko Schocher <hs at denx.de>
> Cc: trini at konsulko.com
> Cc: Heinrich Schuchardt <xypron.glpk at gmx.de>
> Cc: Joel Peshkin <joel.peshkin at broadcom.com>
> To: u-boot at lists.denx.de
>
> ---
> Changes for v2:
>    - Increase MAX_DELAY_STOP_STR
>    - Check salt size against MAX_DELAY_STOP_STR before copying
>    - Minor cleanup
> ---
>  common/Kconfig.boot |  5 ++++-
>  common/autoboot.c   | 12 ++++++++++--
>  2 files changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/common/Kconfig.boot b/common/Kconfig.boot
> index 3f6d9c1..8a98672 100644
> --- a/common/Kconfig.boot
> +++ b/common/Kconfig.boot
> @@ -819,7 +819,10 @@ config AUTOBOOT_STOP_STR_SHA256
>           This option adds the feature to only stop the autobooting,
>           and therefore boot into the U-Boot prompt, when the input
>           string / password matches a values that is encypted via
> -         a SHA256 hash and saved in the environment.
> +         a SHA256 hash and saved in the environment variable
> +         "bootstopkeysha256". If the value in that variable
> +         includes a ":", the portion prior to the ":" will be treated
> +         as a salt value.
>
>  config AUTOBOOT_USE_MENUKEY
>         bool "Allow a specify key to run a menu from the environment"
> diff --git a/common/autoboot.c b/common/autoboot.c
> index e628baf..982b561 100644
> --- a/common/autoboot.c
> +++ b/common/autoboot.c
> @@ -25,7 +25,7 @@
>
>  DECLARE_GLOBAL_DATA_PTR;
>
> -#define MAX_DELAY_STOP_STR 32
> +#define MAX_DELAY_STOP_STR 64
>
>  #ifndef DEBUG_BOOTKEYS
>  #define DEBUG_BOOTKEYS 0
> @@ -80,6 +80,7 @@ static int passwd_abort_sha256(uint64_t etime)
>         u8 sha_env[SHA256_SUM_LEN];
>         u8 *sha;
>         char *presskey;
> +       char *c;
>         const char *algo_name = "sha256";
>         u_int presskey_len = 0;
>         int abort = 0;
> @@ -89,6 +90,14 @@ static int passwd_abort_sha256(uint64_t etime)
>         if (sha_env_str == NULL)
>                 sha_env_str = AUTOBOOT_STOP_STR_SHA256;
>
> +       presskey = malloc_cache_aligned(MAX_DELAY_STOP_STR);
> +       c = strstr(sha_env_str, ":");
> +       if ((c) && (c - sha_env_str < MAX_DELAY_STOP_STR)) {
> +               /* preload presskey with salt */
> +               memcpy(presskey, sha_env_str, c - sha_env_str);
> +               presskey_len = c - sha_env_str;
> +               sha_env_str = c + 1;
> +       }
>         /*
>          * Generate the binary value from the environment hash value
>          * so that we can compare this value with the computed hash
> @@ -100,7 +109,6 @@ static int passwd_abort_sha256(uint64_t etime)
>                 return 0;
>         }
>
> -       presskey = malloc_cache_aligned(MAX_DELAY_STOP_STR);
>         sha = malloc_cache_aligned(SHA256_SUM_LEN);
>         size = SHA256_SUM_LEN;
>         /*
> --
> 1.8.3.1
>
>
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