Re: [PATCH] Fix security issue when reading username and password

[Daniel Kiper]

On Fri, Oct 18, 2019 at 02:39:01PM +0200, Javier Martinez Canillas wrote:
> From: Hector Marco-Gisbert <address@hidden>
>
>   This patch fixes two integer underflows at:
>     * grub-core/lib/crypto.c
>     * grub-core/normal/auth.c
>
> Resolves: CVE-2015-8370
>
> Signed-off-by: Hector Marco-Gisbert <address@hidden>
> Signed-off-by: Ismael Ripoll-Ripoll <address@hidden>
> Signed-off-by: Javier Martinez Canillas <address@hidden>
> ---
>
>  grub-core/lib/crypto.c  | 2 +-
>  grub-core/normal/auth.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/grub-core/lib/crypto.c b/grub-core/lib/crypto.c
> index ca334d5a40e..e6c78d16d39 100644
> --- a/grub-core/lib/crypto.c
> +++ b/grub-core/lib/crypto.c
> @@ -468,7 +468,7 @@ grub_password_get (char buf[], unsigned buf_size)
>         break;
>       }
>
> -      if (key == '\b')
> +      if (key == '\b' && cur_len)
>       {
>         if (cur_len)
>           cur_len--;
> diff --git a/grub-core/normal/auth.c b/grub-core/normal/auth.c
> index 6be678c0de1..c35ce972473 100644
> --- a/grub-core/normal/auth.c
> +++ b/grub-core/normal/auth.c
> @@ -172,7 +172,7 @@ grub_username_get (char buf[], unsigned buf_size)
>         break;
>       }
>
> -      if (key == GRUB_TERM_BACKSPACE)
> +      if (key == GRUB_TERM_BACKSPACE && cur_len)
>       {
>         if (cur_len)
>           {

TBH, I do not understand how this patch helps. It only delays continue
execution to the next "if (!grub_isprint (key))" if cur_len == 0.

Daniel