bug script: Optionally use sudo to read a restricted kernel log

If kernel.dmesg_restrict is enabled (which it now will be by default)
and sudo is installed, ask whether to use sudo.  If this is denied or
fails then fall back to writing a placeholder in the bug report.

debian/changelog

@@ -21,6 +21,8 @@ linux (4.8-1~exp1) UNRELEASED; urgency=medium
   * Compile with gcc-6 on all architectures
   * security,printk: Enable SECURITY_DMESG_RESTRICT, preventing non-root users
     reading the kernel log by default (sysctl: kernel.dmesg_restrict)
+  * bug script: Optionally use sudo to read a restricted kernel log, and fall
+    back to writing a placeholder
 
  -- Ben Hutchings <ben@decadent.org.uk>  Sat, 01 Oct 2016 21:51:33 +0100
 

debian/templates/image.bug/include-dmesg

@@ -1,6 +1,15 @@
 add_dmesg() {
+  local got_log=
   echo '** Kernel log:' >&3
-  dmesg | tail -n 100 >&3
+  if [ "$(cat /proc/sys/kernel/dmesg_restrict)" = 0 ]; then
+    dmesg > >(tail -n 100 >&3) && got_log=y
+  elif command -v sudo >/dev/null; then
+    yesno "Use sudo to read the kernel log? " yep
+    if [ "$REPLY" = yep ]; then
+      sudo dmesg > >(tail -n 100 >&3) && got_log=y
+    fi
+  fi
+  test "$got_log" || echo 'Unable to read kernel log; any relevant messages should be attached' >&3
   echo >&3
 }