dropbear with PAM support - Unable to do ssh.

Sriram sriram.ec at gmail.com
Wed May 10 01:08:28 AWST 2017


Hello,

I m facing a problem when I am trying to use dropbear with PAM support.

My requirement is to restrict certain users to do ssh only through certain
interfaces.
for ex: my board has 2 ip's 10.207.18.101/24 on eth0 and 10.207.118.101/24
on eth1.
dropbear server listens on port 22 on both of these interfaces. Given this
scenario, I want to restrict a particular user say "abc" to be able to do
ssh only through eth1 network.
like "abc" should be able to login from ip's like 10.207.118.102/24,
10.207.118.103/24 etc.,

I didnt find a way to do using only dropbear. So had to integrate dropbear
with PAM.

I applied this patch to dropbear-2016.74.tar.bz2
--- a/options.h
+++ b/options.h
@@ -213,10 +213,10 @@ If you test it please contact the Dropbear author */

 /* This requires crypt() */
 #ifdef HAVE_CRYPT
-#define ENABLE_SVR_PASSWORD_AUTH
+/*#define ENABLE_SVR_PASSWORD_AUTH*/
 #endif
 /* PAM requires ./configure --enable-pam */
-/*#define ENABLE_SVR_PAM_AUTH */
+#define ENABLE_SVR_PAM_AUTH
 #define ENABLE_SVR_PUBKEY_AUTH


Configured and compiled dropbear with PAM support.
I added below configuration files.

a. cat /etc/pam.d/sshd

     auth required pam_unix.so
     account required pam_access.so

b. cat /etc/security/access.conf

    + : root : ALL
    + : abc : 10.207.118.0/24
    - :  abc : 10.207.18.0/24
    - : ALL : ALL

But with this configuration, abc is unable to login to the machine via
10.207.118.0/24 also.
Any idea on how to fix this one ?

Apologies if its not the right forum to ask this question.

Regards,
Sriram.
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