From: Aki Tuomi <aki.tuomi@dovecot.fi>
Date: Wed, 19 Oct 2016 15:44:35 +0000 (+0300)
Subject: lib: Add drop_setuid_root for restrict_access
X-Git-Tag: 2.3.0.rc1~2853
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ea42ee9ebd6f96e771c16e3fee705fa2e6fe609d;p=thirdparty%2Fdovecot%2Fcore.git

lib: Add drop_setuid_root for restrict_access

drop_setuid_root, when set to true, will detect
and try to drop getuid()==0. This is done by
recovering current effective UID to set->uid
if set->uid == -1, and then doing seteuid(0).
It will also drop out any other extra privileges,
such as extra groups not requested for.
---

diff --git a/src/lib/restrict-access.c b/src/lib/restrict-access.c
index 1f4cb1fe99..bb386bdcde 100644
--- a/src/lib/restrict-access.c
+++ b/src/lib/restrict-access.c
@@ -263,6 +263,20 @@ void restrict_access(const struct restrict_access_settings *set,
 
 	is_root = geteuid() == 0;
 
+	if (!is_root &&
+	    set->drop_setuid_root &&
+	    getuid() == 0) {
+		/* recover current effective UID */
+		if (set->uid == (uid_t)-1)
+			set->uid = geteuid();
+		else
+			i_assert(set->uid > 0);
+		/* try to elevate to root */
+		if (seteuid(0) < 0)
+			i_fatal("seteuid(0) failed: %m");
+		is_root = TRUE;
+	}
+
 	/* set the primary/privileged group */
 	process_primary_gid = set->gid;
 	process_privileged_gid = set->privileged_gid;
diff --git a/src/lib/restrict-access.h b/src/lib/restrict-access.h
index 485760cab1..a60b9a723f 100644
--- a/src/lib/restrict-access.h
+++ b/src/lib/restrict-access.h
@@ -25,6 +25,10 @@ struct restrict_access_settings {
 
 	/* Chroot directory */
 	const char *chroot_dir;
+
+	/* Set TRUE to attempt to drop any root privileges
+	   FIXME: Reverse logic on v2.3 */
+	bool drop_setuid_root; 
 };
 
 /* Initialize settings with values that don't change anything. */