linux-kernel - Re: [PATCH v1 1/2] certs: Remove panic() calls from blacklist

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Date:   Fri, 11 Mar 2022 17:00:32 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Mickaël Salaün <mic@...ikod.net>,
        Jarkko Sakkinen <jarkko@...nel.org>
Cc:     David Howells <dhowells@...hat.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Snowberg <eric.snowberg@...cle.com>,
        Mickaël Salaün <mic@...ux.microsoft.com>,
        keyrings@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/2] certs: Remove panic() calls from blacklist_init()

On Fri, Mar 11, 2022 at 12:47 PM Mickaël Salaün <mic@...ikod.net> wrote:
> From: Mickaël Salaün <mic@...ux.microsoft.com>
>
> Replace panic() calls from device_initcall(blacklist_init) with proper
> error handling using -ENODEV.
>
> Suggested-by: Jarkko Sakkinen <jarkko@...nel.org> [1]
> Link: https://lore.kernel.org/r/Yik0C2t7G272YZ73@iki.fi [1]
> Signed-off-by: Mickaël Salaün <mic@...ux.microsoft.com>
> Link: https://lore.kernel.org/r/20220311174741.250424-2-mic@digikod.net
> ---
>  certs/blacklist.c | 27 +++++++++++++++++++++------
>  1 file changed, 21 insertions(+), 6 deletions(-)

I'm not sure we can safely rely on a non-zero error code saving us in
the care of failure, can we?

The blacklist_init() function is registered as an initcall via
device_initcall() which I believe is either executed via
do_init_module() in the case of a dynamic module load, or via
do_initcalls() if built into the kernel.  In either case the result is
that the module/functionality doesn't load and the kernel continues on
executing.  While this could be acceptable for some non-critical
modules, if this particular module fails to load it defeats the
certificate/key based deny list for signed modules, yes?

I completely understand the strong desire to purge the kernel of
panic()s, BUG()s, and the like, but if a critical piece of security
functionality that users expect to be present fails to initialize,
panic()ing is likely the right thing to do.

> diff --git a/certs/blacklist.c b/certs/blacklist.c
> index 486ce0dd8e9c..ea7a77f156da 100644
> --- a/certs/blacklist.c
> +++ b/certs/blacklist.c
> @@ -313,12 +313,16 @@ static int __init blacklist_init(void)
>         const char *const *bl;
>         struct key_restriction *restriction;
>
> -       if (register_key_type(&key_type_blacklist) < 0)
> -               panic("Can't allocate system blacklist key type\n");
> +       if (register_key_type(&key_type_blacklist) < 0) {
> +               pr_err("Can't allocate system blacklist key type\n");
> +               return -ENODEV;
> +       }
>
>         restriction = kzalloc(sizeof(*restriction), GFP_KERNEL);
> -       if (!restriction)
> -               panic("Can't allocate blacklist keyring restriction\n");
> +       if (!restriction) {
> +               pr_err("Can't allocate blacklist keyring restriction\n");
> +               goto err_restriction;
> +       }
>         restriction->check = restrict_link_for_blacklist;
>
>         blacklist_keyring =
> @@ -333,13 +337,24 @@ static int __init blacklist_init(void)
>                               , KEY_ALLOC_NOT_IN_QUOTA |
>                               KEY_ALLOC_SET_KEEP,
>                               restriction, NULL);
> -       if (IS_ERR(blacklist_keyring))
> -               panic("Can't allocate system blacklist keyring\n");
> +       if (IS_ERR(blacklist_keyring)) {
> +               pr_err("Can't allocate system blacklist keyring\n");
> +               goto err_keyring;
> +       }
>
>         for (bl = blacklist_hashes; *bl; bl++)
>                 if (mark_raw_hash_blacklisted(*bl) < 0)
>                         pr_err("- blacklisting failed\n");
>         return 0;
> +
> +
> +err_keyring:
> +       kfree(restriction);
> +
> +err_restriction:
> +       unregister_key_type(&key_type_blacklist);
> +
> +       return -ENODEV;
>  }

-- 
paul-moore.com