added library for privilege separation

git-svn-id: svn://svn.alpinelinux.org/acf/core/trunk@306 ab2d0c66-481e-0410-8bed-d214d4d58bed

1 files changed, 75 insertions, 0 deletions

diff --git a/lib/privsep.lua b/lib/privsep.lua
new file mode 100644
index 0000000..d2edcb7
--- /dev/null
+++ b/lib/privsep.lua
@@ -0,0 +1,75 @@
+
+module(..., package.seeall)
+
+require("json")
+require("posix")
+
+local rpc = {}
+
+-- private privileged rpc server ------------------------------------
+local function rpcserver(r, w)
+	for line in r:lines() do
+		local handle = json.decode(line)
+		if type(rpc[handle.func]) == "function" then
+			response = rpc[handle.func](unpack(handle.data))
+		else
+			response = nil
+		end
+		w:write(json.encode(response).."\n")
+		w:flush()
+	end
+end
+
+
+-- public func ---------------------------------------------------- 
+function drop_privs(user, group, privileged_funcs)
+	local k, v
+	local wrapper = {}
+
+	-- communication pipes
+	local cr, pw = posix.pipe()
+	local pr, cw = posix.pipe()
+
+	-- create wrapper table
+	for k,v in pairs(privileged_funcs or {}) do
+		if type(v) == "function" then
+			rpc[k] = v
+			wrapper[k] = function(...)
+				local handle = {}
+				handle.func = k
+				handle.data = {...}
+				cw:write(json.encode(handle).."\n")
+				cw:flush()
+				return (json.decode(cr:read("*line")))
+			end
+		end
+	end
+			
+	pid = posix.fork()
+	if pid == nil then
+		cr:close()
+		cw:close()
+		pr:close()
+		cw:close()
+		return nil
+	end
+
+	if pid == 0 then
+		-- child runs with privs
+		cr:close()
+		cw:close()
+		rpcserver(pr, pw)
+		pw:close()
+		pr:close()
+		os.exit()
+	end
+
+	-- lets drop privs
+	if posix.setpid("g", group) and	posix.setpid("u", user) then
+		return wrapper
+	else
+		posix.kill(pid)
+		return nil
+	end
+end
+