[PATCH] audit: always check the netlink payload length in audit_receive_msg()

[Paul Moore]

On Mon, Feb 24, 2020 at 5:53 PM Paul Moore <paul at paul-moore.com> wrote:
>
> This patch ensures that we always check the netlink payload length
> in audit_receive_msg() before we take any action on the payload
> itself.
>
> Cc: stable at vger.kernel.org
> Reported-by: syzbot+399c44bf1f43b8747403 at syzkaller.appspotmail.com
> Reported-by: syzbot+e4b12d8d202701f08b6d at syzkaller.appspotmail.com
> Signed-off-by: Paul Moore <paul at paul-moore.com>
> ---
>  kernel/audit.c |   43 +++++++++++++++++++++++--------------------
>  1 file changed, 23 insertions(+), 20 deletions(-)

...

> diff --git a/kernel/audit.c b/kernel/audit.c
> index 17b0d523afb3..6e8b176bdb68 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -1334,26 +1339,24 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
>                                         break;
>                         }
>                         audit_log_user_recv_msg(&ab, msg_type);
> -                       if (msg_type != AUDIT_USER_TTY)
> +                       if (msg_type != AUDIT_USER_TTY) {
> +                               /* ensure NULL termination */
> +                               str[data_len - 1] = '\0';
>                                 audit_log_format(ab, " msg='%.*s'",
>                                                  AUDIT_MESSAGE_TEXT_MAX,
> -                                                (char *)data);
> -                       else {
> -                               int size;
> -
> +                                                str);
> +                       } else {
>                                 audit_log_format(ab, " data=");
> -                               size = nlmsg_len(nlh);
> -                               if (size > 0 &&
> -                                   ((unsigned char *)data)[size - 1] == '\0')
> -                                       size--;
> -                               audit_log_n_untrustedstring(ab, data, size);
> +                               if (data_len > 0 && str[data_len - 1] == '\0')
> +                                       data_len--;
> +                               audit_log_n_untrustedstring(ab, data, data_len);
                                                                  ^^^^
... and it looks like I didn't properly refresh my patch before
sending, the second arg in the line above is "str" not "data".

-- 
paul moore
www.paul-moore.com