gnu: shadow: Fix CVE-2017-2616.

* gnu/packages/patches/shadow-CVE-2017-2616.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/admin.scm (shadow): Use it.

gnu/local.mk

@@ -901,6 +901,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/serf-comment-style-fix.patch		\
   %D%/packages/patches/serf-deflate-buckets-test-fix.patch	\
   %D%/packages/patches/shadow-4.4-su-snprintf-fix.patch         \
+  %D%/packages/patches/shadow-CVE-2017-2616.patch		\
   %D%/packages/patches/slim-session.patch			\
   %D%/packages/patches/slim-config.patch			\
   %D%/packages/patches/slim-sigusr1.patch			\

gnu/packages/admin.scm

@@ -276,7 +276,8 @@ client and server, a telnet client and server, and an rsh client and server.")
               (uri (string-append
                     "https://github.com/shadow-maint/shadow/releases/"
                     "download/" version "/shadow-" version ".tar.xz"))
-              (patches (search-patches "shadow-4.4-su-snprintf-fix.patch"))
+              (patches (search-patches "shadow-4.4-su-snprintf-fix.patch"
+                                       "shadow-CVE-2017-2616.patch"))
               (sha256
                (base32
                 "0g7hf55ar2pafg5g3ldx0fwzjk36wf4xb21p4ndanbjm3c2a9ab1"))))

gnu/packages/patches/shadow-CVE-2017-2616.patch

@@ -0,0 +1,72 @@
+Fix CVE-2017-2616:
+
+https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-2616
+http://seclists.org/oss-sec/2017/q1/490
+http://seclists.org/oss-sec/2017/q1/474
+
+Patch copied from upstream source repository:
+
+https://github.com/shadow-maint/shadow/commit/08fd4b69e84364677a10e519ccb25b71710ee686
+
+From 08fd4b69e84364677a10e519ccb25b71710ee686 Mon Sep 17 00:00:00 2001
+From: Tobias Stoeckmann <tobias@stoeckmann.org>
+Date: Thu, 23 Feb 2017 09:47:29 -0600
+Subject: [PATCH] su: properly clear child PID
+
+If su is compiled with PAM support, it is possible for any local user
+to send SIGKILL to other processes with root privileges. There are
+only two conditions. First, the user must be able to perform su with
+a successful login. This does NOT have to be the root user, even using
+su with the same id is enough, e.g. "su $(whoami)". Second, SIGKILL
+can only be sent to processes which were executed after the su process.
+It is not possible to send SIGKILL to processes which were already
+running. I consider this as a security vulnerability, because I was
+able to write a proof of concept which unlocked a screen saver of
+another user this way.
+---
+ src/su.c | 19 +++++++++++++++++--
+ 1 file changed, 17 insertions(+), 2 deletions(-)
+
+diff --git a/src/su.c b/src/su.c
+index f20d230..d86aa86 100644
+--- a/src/su.c
++++ b/src/su.c
+@@ -379,11 +379,13 @@ static void prepare_pam_close_session (void)
+ 				/* wake child when resumed */
+ 				kill (pid, SIGCONT);
+ 				stop = false;
++			} else {
++				pid_child = 0;
+ 			}
+ 		} while (!stop);
+ 	}
+ 
+-	if (0 != caught) {
++	if (0 != caught && 0 != pid_child) {
+ 		(void) fputs ("\n", stderr);
+ 		(void) fputs (_("Session terminated, terminating shell..."),
+ 		              stderr);
+@@ -393,9 +395,22 @@ static void prepare_pam_close_session (void)
+ 		snprintf (wait_msg, sizeof wait_msg, _(" ...waiting for child to terminate.\n"));
+ 
+ 		(void) signal (SIGALRM, kill_child);
++		(void) signal (SIGCHLD, catch_signals);
+ 		(void) alarm (2);
+ 
+-		(void) wait (&status);
++		sigemptyset (&ourset);
++		if ((sigaddset (&ourset, SIGALRM) != 0)
++		    || (sigprocmask (SIG_BLOCK, &ourset, NULL) != 0)) {
++			fprintf (stderr, _("%s: signal masking malfunction\n"), Prog);
++			kill_child (0);
++		} else {
++			while (0 == waitpid (pid_child, &status, WNOHANG)) {
++				sigsuspend (&ourset);
++			}
++			pid_child = 0;
++			(void) sigprocmask (SIG_UNBLOCK, &ourset, NULL);
++		}
++
+ 		(void) fputs (_(" ...terminated.\n"), stderr);
+ 	}
+