Hi,
Thanks for the patch. It looks useful, though I plan to
update Dropbear to full PAM handling (with
keyboard-interactive mode) soon, which should handle this
case as well. If I don't get that done I'll put the patch in
the next release.
My one concern is how clients might deal with multiple
banner messages - have you tried with many clients?
Cheers,
Matt
On Thu, May 02, 2013 at 11:44:10AM +0100, Martin Donnelly wrote:
> This patch adds support for relaying PAM_ERROR_MSG to clients. This
> is useful when PAM_ERROR_MSG returns meaningful information, an
> example of this is when pam_nologin is being used and '/etc/nologin'
> contains a message for clients attempting to connect.
>
> -Martin
> diff -ubNr dropbear-2013.58.orig/auth.h dropbear-2013.58/auth.h
> --- dropbear-2013.58.orig/auth.h 2013-04-18 15:58:14.000000000 +0100
> +++ dropbear-2013.58/auth.h 2013-04-30 17:37:33.317480220 +0100
> @@ -36,6 +36,7 @@
> void recv_msg_userauth_request();
> void send_msg_userauth_failure(int partial, int incrfail);
> void send_msg_userauth_success();
> +void send_msg_userauth_banner(buffer **msg);
> void svr_auth_password();
> void svr_auth_pubkey();
> void svr_auth_pam();
> diff -ubNr dropbear-2013.58.orig/common-session.c
> dropbear-2013.58/common-session.c
> --- dropbear-2013.58.orig/common-session.c 2013-04-18 15:58:14.000000000
> +0100
> +++ dropbear-2013.58/common-session.c 2013-05-01 15:55:20.687368142 +0100
> @@ -122,6 +122,8 @@
>
> ses.allowprivport = 0;
>
> + ses.pam_err = NULL;
> +
> TRACE(("leave session_init"))
> }
>
> diff -ubNr dropbear-2013.58.orig/session.h dropbear-2013.58/session.h
> --- dropbear-2013.58.orig/session.h 2013-04-18 15:58:14.000000000 +0100
> +++ dropbear-2013.58/session.h 2013-05-02 11:32:32.610072021 +0100
> @@ -197,6 +197,8 @@
> * really belong here, but nowhere else fits nicely */
> int allowprivport;
>
> + /* buffer for storing PAM error messages */
> + buffer * pam_err;
> };
>
> struct serversession {
> diff -ubNr dropbear-2013.58.orig/svr-auth.c dropbear-2013.58/svr-auth.c
> --- dropbear-2013.58.orig/svr-auth.c 2013-04-18 15:58:14.000000000 +0100
> +++ dropbear-2013.58/svr-auth.c 2013-05-01 17:36:28.249791834 +0100
> @@ -37,7 +37,6 @@
>
> static void authclear();
> static int checkusername(unsigned char *username, unsigned int userlen);
> -static void send_msg_userauth_banner();
>
> /* initialise the first time for a session, resetting all parameters */
> void svr_authinitialise() {
> @@ -82,10 +81,10 @@
>
> /* Send a banner message if specified to the client. The client might
> * ignore this, but possibly serves as a legal "no trespassing" sign */
> -static void send_msg_userauth_banner() {
> +void send_msg_userauth_banner(buffer **banner) {
>
> TRACE(("enter send_msg_userauth_banner"))
> - if (svr_opts.banner == NULL) {
> + if ((banner == NULL) || (*banner == NULL)) {
> TRACE(("leave send_msg_userauth_banner: banner is NULL"))
> return;
> }
> @@ -93,13 +92,13 @@
> CHECKCLEARTOWRITE();
>
> buf_putbyte(ses.writepayload, SSH_MSG_USERAUTH_BANNER);
> - buf_putstring(ses.writepayload, buf_getptr(svr_opts.banner,
> - svr_opts.banner->len), svr_opts.banner->len);
> + buf_putstring(ses.writepayload, buf_getptr(*banner,
> + (*banner)->len), (*banner)->len);
> buf_putstring(ses.writepayload, "en", 2);
>
> encrypt_packet();
> - buf_free(svr_opts.banner);
> - svr_opts.banner = NULL;
> + buf_free(*banner);
> + *banner = NULL;
>
> TRACE(("leave send_msg_userauth_banner"))
> }
> @@ -121,7 +120,7 @@
>
> /* send the banner if it exists, it will only exist once */
> if (svr_opts.banner) {
> - send_msg_userauth_banner();
> + send_msg_userauth_banner(&svr_opts.banner);
> }
>
>
> diff -ubNr dropbear-2013.58.orig/svr-authpam.c dropbear-2013.58/svr-authpam.c
> --- dropbear-2013.58.orig/svr-authpam.c 2013-04-18 15:58:14.000000000
> +0100
> +++ dropbear-2013.58/svr-authpam.c 2013-05-01 15:18:38.603729862 +0100
> @@ -142,6 +142,22 @@
> (*respp) = resp;
> break;
>
> + case PAM_ERROR_MSG:
> +
> + if (msg_len > 0) {
> + ses.pam_err = buf_new(msg_len + 4);
> + buf_setpos(ses.pam_err, 0);
> + buf_putbytes(ses.pam_err, "\r\n", 2);
> + buf_putbytes(ses.pam_err, (*msg)->msg, msg_len);
> + buf_putbytes(ses.pam_err, "\r\n", 2);
> + buf_setpos(ses.pam_err, 0);
> +
> + send_msg_userauth_banner(&ses.pam_err);
> + }
> +
> + rc = PAM_AUTH_ERR;
> + break;
> +
> default:
> TRACE(("Unknown message type"))
> rc = PAM_CONV_ERR;
