gnu: screen: Fix CVE-2017-5618.

* gnu/packages/patches/screen-CVE-2017-5618.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/screen.scm (screen)[source]: Use it.

gnu/local.mk

@@ -891,6 +891,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/sed-hurd-path-max.patch			\
   %D%/packages/patches/scheme48-tests.patch			\
   %D%/packages/patches/scotch-test-threading.patch		\
+  %D%/packages/patches/screen-CVE-2017-5618.patch		\
   %D%/packages/patches/sdl-libx11-1.6.patch			\
   %D%/packages/patches/seq24-rename-mutex.patch			\
   %D%/packages/patches/serf-comment-style-fix.patch		\

gnu/packages/patches/screen-CVE-2017-5618.patch

@@ -0,0 +1,40 @@
+Fixes CVE-2017-5618 (privilege escalation via opening the logfile when
+screen is installed setuid root):
+
+https://savannah.gnu.org/bugs/?50142
+https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-5618
+
+This patch reverts the upstream commit that introduced the bug:
+
+https://git.savannah.gnu.org/cgit/screen.git/commit/?id=5460f5d28c01a9a58e021eb1dffef2965e629d58
+
+From f55b0cc29a0ac2a1c54e8a5e886b7393edd4a76c Mon Sep 17 00:00:00 2001
+From: Leo Famulari <leo@famulari.name>
+Date: Sat, 11 Feb 2017 22:40:24 -0500
+Subject: [PATCH] Revert "adding permissions check for the logfile name"
+
+This reverts commit 5460f5d28c01a9a58e021eb1dffef2965e629d58.
+---
+ src/screen.c | 6 ------
+ 1 file changed, 6 deletions(-)
+
+diff --git a/src/screen.c b/src/screen.c
+index 64650e9..283c305 100644
+--- a/src/screen.c
++++ b/src/screen.c
+@@ -673,12 +673,6 @@ int main(int ac, char** av)
+                 Panic(0, "-L: logfile name can not start with \"-\" symbol");
+               if (strlen(screenlogfile) > PATH_MAX)
+                 Panic(0, "-L: logfile name too long. (max. %d char)", PATH_MAX);
+-
+-              FILE *w_check;
+-              if ((w_check = fopen(screenlogfile, "w")) == NULL)
+-                Panic(0, "-L: logfile name access problem");
+-              else
+-                fclose(w_check);
+             }
+             nwin_options.Lflag = 1;
+             break;
+-- 
+2.11.1
+

gnu/packages/screen.scm

@@ -40,6 +40,8 @@
              (method url-fetch)
              (uri (string-append "mirror://gnu/screen/screen-"
                                  version ".tar.gz"))
+             (patches (search-patches "screen-CVE-2017-5618.patch"))
+             (patch-flags '("-p2"))
              (sha256
               (base32 "1c7grw03a9iwvqbxfd6hmjb681rp8gb55zsxm7b3apqqcb1sghq1"))))
     (build-system gnu-build-system)