DigitalOcean.distroKernel property now reboots into the distribution kernel when necessary.

It might be better to do this check on boot to limit the time running the
DO kernel (which is not well security supported), but that has the
possibility of entering a bad reboot loop. Limiting this check to when
propellor runs avoids that, while still fixing the problem pretty fast.

debian/changelog

@@ -5,6 +5,8 @@ propellor (0.9.3) UNRELEASED; urgency=medium
   * When multiple gpg keys are added, ensure that the privdata file
     can be decrypted by all of them.
   * Convert GpgKeyId to newtype.
+  * DigitalOcean.distroKernel property now reboots into the distribution
+    kernel when necessary.
 
  -- Joey Hess <joeyh@debian.org>  Mon, 10 Nov 2014 11:15:27 -0400
 

src/Propellor/Property/HostingProvider/DigitalOcean.hs

@@ -1,21 +1,50 @@
-module Propellor.Property.HostingProvider.DigitalOcean where
+module Propellor.Property.HostingProvider.DigitalOcean (
+	distroKernel
+) where
 
 import Propellor
 import qualified Propellor.Property.Apt as Apt
 import qualified Propellor.Property.File as File
 
+import Data.List
+
 -- Digital Ocean does not provide any way to boot
 -- the kernel provided by the distribution, except using kexec.
 -- Without this, some old, and perhaps insecure kernel will be used.
 --
--- Note that this only causes the new kernel to be loaded on reboot.
--- If the power is cycled, the old kernel still boots up.
--- TODO: detect this and reboot immediately?
+-- This property causes the distro kernel to be loaded on reboot, using kexec.
+--
+-- If the power is cycled, the non-distro kernel still boots up.
+-- So, this property also checks if the running kernel is present in /boot,
+-- and if not, reboots immediately into a distro kernel.
 distroKernel :: Property
 distroKernel = propertyList "digital ocean distro kernel hack"
-	[ Apt.installed ["grub-pc", "kexec-tools"]
+	[ Apt.installed ["grub-pc", "kexec-tools", "file"]
 	, "/etc/default/kexec" `File.containsLines`
 		[ "LOAD_KEXEC=true"
 		, "USE_GRUB_CONFIG=true"
 		] `describe` "kexec configured"
+	, check (not <$> runningInstalledKernel)
+		(cmdProperty "reboot" [])
+			`describe` "running installed kernel"
 	]
+
+runningInstalledKernel :: IO Bool
+runningInstalledKernel = do
+	kernelver <- takeWhile (/= '\n') <$> readProcess "uname" ["-r"]
+	when (null kernelver) $
+		error "failed to read uname -r"
+	kernelimages <- concat <$> mapM kernelsIn ["/", "/boot/"] 
+	when (null kernelimages) $
+		error "failed to find any installed kernel images"
+	findVersion kernelver <$>
+		readProcess "file" ("-L" : kernelimages)
+
+-- File output looks something like this, we want to unambiguously
+-- match the running kernel version:
+--   Linux kernel x86 boot executable bzImage, version 3.16-3-amd64 (debian-kernel@lists.debian.org) #1 SMP Debian 3.1, RO-rootFS, swap_dev 0x2, Normal VGA
+findVersion :: String -> String -> Bool
+findVersion ver s = (" version " ++ ver ++ " ") `isInfixOf` s
+
+kernelsIn :: FilePath -> IO [FilePath]
+kernelsIn d = filter ("vmlinu" `isInfixOf`) <$> dirContents d