gnu: linux-pam: Change path to unix_chkpwd helper.

* gnu/packages/patches/linux-pam-unix_chkpwd.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/linux.scm (linux-pam): Use it.
* gnu/system/pam.scm (pam-root-service-type): Add unix_chkpwd to setuid.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>

gnu/local.mk

@@ -1433,6 +1433,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/linux-libre-support-for-Pinebook-Pro.patch \
   %D%/packages/patches/linux-libre-arm64-generic-pinebook-lcd.patch \
   %D%/packages/patches/linux-pam-no-setfsuid.patch		\
+  %D%/packages/patches/linux-pam-unix_chkpwd.patch		\
   %D%/packages/patches/linuxdcpp-openssl-1.1.patch		\
   %D%/packages/patches/lirc-localstatedir.patch			\
   %D%/packages/patches/lirc-reproducible-build.patch		\

gnu/packages/linux.scm

@@ -1596,7 +1596,8 @@ which need to be installed separately.")
        (sha256
         (base32
          "1z4jayf69qyyxln1gl6ch4qxfd66ib1g42garnrv2d8i1drl0790"))
-       (patches (search-patches "linux-pam-no-setfsuid.patch"))))
+       (patches (search-patches "linux-pam-unix_chkpwd.patch"
+                                "linux-pam-no-setfsuid.patch"))))
 
     (build-system gnu-build-system)
     (native-inputs

gnu/packages/patches/linux-pam-unix_chkpwd.patch

@@ -0,0 +1,9 @@
+unix_chkpwd is designed to have a suid bit, but it's not possible to set it
+for files in the store.  This patch tells unix_pam.so to look for
+unix_chkpwd in setuid program directory on Guix System.
+
+--- a/modules/pam_unix/Makefile.in
++++ b/modules/pam_unix/Makefile.in
+@@ -651,1 +651,1 @@
+-	-DCHKPWD_HELPER=\"$(sbindir)/unix_chkpwd\" \
++	-DCHKPWD_HELPER=\"/run/setuid-programs/unix_chkpwd\" \

gnu/system/pam.scm

@@ -21,6 +21,7 @@
   #:use-module (guix derivations)
   #:use-module (guix gexp)
   #:use-module (gnu services)
+  #:use-module (gnu system setuid)
   #:use-module (ice-9 match)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-9)
@@ -375,8 +376,13 @@ strings or string-valued gexps."
 
 (define pam-root-service-type
   (service-type (name 'pam)
-                (extensions (list (service-extension etc-service-type
-                                                     /etc-entry)))
+                (extensions
+                 (list (service-extension
+                        setuid-program-service-type
+                        (lambda (_)
+                          (list (file-like->setuid-program
+                                 (file-append linux-pam "/sbin/unix_chkpwd")))))
+                       (service-extension etc-service-type /etc-entry)))
 
                 ;; Arguments include <pam-service> as well as procedures.
                 (compose concatenate)