From 94fd4986c3a2b2b583113c3ccb2af3276b49c27d Mon Sep 17 00:00:00 2001 From: Raphael Hertzog Date: Mon, 9 Jul 2018 16:27:53 +0200 Subject: Add /usr/sbin and /sbin to default root PATH When dropbear is used in a very restricted environment (such as in a initrd), the default user shell is often also very restricted and doesn't take care of setting the PATH so the user ends up with the PATH set by dropbear. Unfortunately, dropbear always sets "/usr/bin:/bin" as default PATH even for the root user which should have /usr/sbin and /sbin too. For a concrete instance of this problem, see the "Remote Unlocking" section in this tutorial: https://paxswill.com/blog/2013/11/04/encrypted-raspberry-pi/ It speaks of a bug in the initramfs script because it's written "blkid" instead of "/sbin/blkid"... this is just because the scripts from the initramfs do not expect to have a PATH without the sbin directories and because dropbear is not setting the PATH appropriately for the root user. I'm thus suggesting to use the attached patch to fix this misbehaviour (I did not test it, but it's easy enough). It might seem anecdotic but multiple Kali users have been bitten by this. From https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=903403 --- default_options.h | 1 + svr-chansession.c | 6 +++++- 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/default_options.h b/default_options.h index 8d04506..536f4e7 100644 --- a/default_options.h +++ b/default_options.h @@ -339,5 +339,6 @@ be overridden at runtime with -I. 0 disables idle timeouts */ /* The default path. This will often get replaced by the shell */ #define DEFAULT_PATH "/usr/bin:/bin" +#define DEFAULT_ROOT_PATH "/usr/sbin:/usr/bin:/sbin:/bin" #endif /* DROPBEAR_DEFAULT_OPTIONS_H_ */ diff --git a/svr-chansession.c b/svr-chansession.c index 35631e9..9ae2e60 100644 --- a/svr-chansession.c +++ b/svr-chansession.c @@ -1012,7 +1012,11 @@ static void execchild(const void *user_data) { addnewvar("LOGNAME", ses.authstate.pw_name); addnewvar("HOME", ses.authstate.pw_dir); addnewvar("SHELL", get_user_shell()); - addnewvar("PATH", DEFAULT_PATH); + if (getuid() == 0) { + addnewvar("PATH", DEFAULT_ROOT_PATH); + } else { + addnewvar("PATH", DEFAULT_PATH); + } if (cp != NULL) { addnewvar("LANG", cp); m_free(cp); -- cgit v1.2.1