linux-kernel - Re: [PATCH] integrity: check the return value of audit_log

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Date:   Wed, 12 Jan 2022 12:23:04 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     xkernel.wang@...mail.com
Cc:     jmorris@...ei.org, serge@...lyn.com,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] integrity: check the return value of audit_log_start()

On Tue, Dec 14, 2021 at 12:39 AM <xkernel.wang@...mail.com> wrote:
>
> From: Xiaoke Wang <xkernel.wang@...mail.com>
>
> audit_log_start() returns audit_buffer pointer on success or NULL on
> error, so it is better to check the return value of it to prevent
> potential memory access error.
>
> Signed-off-by: Xiaoke Wang <xkernel.wang@...mail.com>
> ---
>  security/integrity/integrity_audit.c | 38 +++++++++++++++-------------
>  1 file changed, 20 insertions(+), 18 deletions(-)
>
> diff --git a/security/integrity/integrity_audit.c b/security/integrity/integrity_audit.c
> index 2922005..62785d5 100644
> --- a/security/integrity/integrity_audit.c
> +++ b/security/integrity/integrity_audit.c
> @@ -45,23 +45,25 @@ void integrity_audit_message(int audit_msgno, struct inode *inode,
>                 return;
>
>         ab = audit_log_start(audit_context(), GFP_KERNEL, audit_msgno);

As this is IMA code, it's largely up to Mimi about what she would
prefer, but I think a much simpler patch would be to just return early
if ab == NULL, for example:

  ab = audit_log_start( .... , audit_msgno);
  if (!ab)
    return;

> -       audit_log_format(ab, "pid=%d uid=%u auid=%u ses=%u",
> -                        task_pid_nr(current),
> -                        from_kuid(&init_user_ns, current_uid()),
> -                        from_kuid(&init_user_ns, audit_get_loginuid(current)),
> -                        audit_get_sessionid(current));
> -       audit_log_task_context(ab);
> -       audit_log_format(ab, " op=%s cause=%s comm=", op, cause);
> -       audit_log_untrustedstring(ab, get_task_comm(name, current));
> -       if (fname) {
> -               audit_log_format(ab, " name=");
> -               audit_log_untrustedstring(ab, fname);
> +       if (ab) {
> +               audit_log_format(ab, "pid=%d uid=%u auid=%u ses=%u",
> +                               task_pid_nr(current),
> +                               from_kuid(&init_user_ns, current_uid()),
> +                               from_kuid(&init_user_ns, audit_get_loginuid(current)),
> +                               audit_get_sessionid(current));
> +               audit_log_task_context(ab);
> +               audit_log_format(ab, " op=%s cause=%s comm=", op, cause);
> +               audit_log_untrustedstring(ab, get_task_comm(name, current));
> +               if (fname) {
> +                       audit_log_format(ab, " name=");
> +                       audit_log_untrustedstring(ab, fname);
> +               }
> +               if (inode) {
> +                       audit_log_format(ab, " dev=");
> +                       audit_log_untrustedstring(ab, inode->i_sb->s_id);
> +                       audit_log_format(ab, " ino=%lu", inode->i_ino);
> +               }
> +               audit_log_format(ab, " res=%d errno=%d", !result, errno);
> +               audit_log_end(ab);
>         }
> -       if (inode) {
> -               audit_log_format(ab, " dev=");
> -               audit_log_untrustedstring(ab, inode->i_sb->s_id);
> -               audit_log_format(ab, " ino=%lu", inode->i_ino);
> -       }
> -       audit_log_format(ab, " res=%d errno=%d", !result, errno);
> -       audit_log_end(ab);
>  }
> --



-- 
paul moore
www.paul-moore.com