autoupdater: avoid unnessesary shell processes

Use functions that don't run commands though a shell where easily possible,
add 'exec' to remaining io.popen calls.

admin/autoupdater/files/usr/lib/lua/autoupdater/util.lua

@@ -6,8 +6,23 @@ local nixio = require 'nixio'
 module 'autoupdater.util'
 
 
+-- Executes a command in the background, without parsing the command through a shell (in contrast to os.execute)
+function exec(...)
+  local pid, errno, error = nixio.fork()
+  if pid == 0 then
+    nixio.execp(...)
+    os.exit(127)
+  elseif pid > 0 then
+    local wpid, status, code = nixio.waitpid(pid)
+    return wpid and status == 'exited' and code
+  else
+    return pid, errno, error
+  end
+end
+
+
 -- Executes a command in the background, returning its PID and a pipe connected to the command's standard input
-function popen(command)
+function popen(...)
   local inr, inw = nixio.pipe()
   local pid = nixio.fork()
 
@@ -21,7 +36,8 @@ function popen(command)
     inr:close()
     inw:close()
 
-    nixio.exec('/bin/sh', '-c', command)
+    nixio.execp(...)
+    os.exit(127)
   end
 end
 

admin/autoupdater/files/usr/sbin/autoupdater

@@ -80,24 +80,26 @@ end
 
 -- Verifies a file given as a list of lines with a list of signatures using ecdsaverify
 local function verify_lines(lines, sigs)
-  local command = string.format('ecdsaverify -n %i', branch.good_signatures)
+  local command = {'ecdsaverify', '-n', tostring(branch.good_signatures)}
 
   -- Build command line from sigs and branch.pubkey
   for _, sig in ipairs(sigs) do
     if sig:match('^' .. string.rep('%x', 128) .. '$') then
-      command = command .. ' -s ' .. sig
+      table.insert(command, '-s')
+      table.insert(command, sig)
     end
   end
 
   for _, key in ipairs(branch.pubkey) do
     if key:match('^' .. string.rep('%x', 64) .. '$') then
-      command = command .. ' -p ' .. key
+      table.insert(command, '-p')
+      table.insert(command, key)
     end
   end
 
 
   -- Call ecdsautils
-  local pid, f = autoupdater_util.popen(command)
+  local pid, f = autoupdater_util.popen(unpack(command))
 
   for _, line in ipairs(lines) do
     f:write(line)
@@ -126,7 +128,7 @@ local function read_manifest(mirror)
 
   -- Read all lines from the manifest
   -- The upper part is saves to lines, the lower part to sigs
-  for line in io.popen(string.format("wget -T 120 -O- '%s/%s.manifest'", mirror, branch.name), 'r'):lines() do
+  for line in io.popen(string.format("exec wget -T 120 -O- '%s/%s.manifest'", mirror, branch.name), 'r'):lines() do
     if not sep then
       if line == '---' then
         sep = true
@@ -189,7 +191,7 @@ end
 
 -- Downloads the firmware image from a mirror to a given output file
 local function fetch_firmware(mirror, filename, output)
-  if os.execute(string.format("wget -T 120 -O '%s' '%s/%s'", output, mirror, filename)) ~= 0 then
+  if autoupdater_util.exec('wget', '-T', '120', '-O', output, mirror .. '/' .. filename) ~= 0 then
     io.stderr:write('Error downloading the image from ' .. mirror .. '\n')
     return false
   end
@@ -258,7 +260,8 @@ local function autoupdate(mirror)
   end
 
 
-  os.execute('sync; sysctl -w vm.drop_caches=3')
+  autoupdater_util.exec('sync')
+  autoupdater_util.exec('sysctl', '-w', 'vm.drop_caches=3')
   collectgarbage()
 
   local image = os.tmpname()
@@ -266,7 +269,7 @@ local function autoupdate(mirror)
     return false
   end
 
-  local popen = io.popen(string.format("sha512sum '%s'", image))
+  local popen = io.popen(string.format("exec sha512sum '%s'", image))
   local checksum = popen:read('*l'):match('^%x+')
   popen:close()
   if checksum ~= manifest.checksum then