metadata: get and set policies from go

This commit adds in the ability to get and set policy data from go using
the GetPolicy and SetPolicy functions. This is done via a patch of the
x/sys/unix package that exposes the filesystem encryption structures.

Note that not all the fields of the PolicyData protocol buffer are
needed to get and set policies. The wrapped_policy_keys are not used and
will be written and read by other components of fscrypt.

To run the policy tests, the environment variable BASE_TEST_DIR must be
set to a directory for testing on a filesystem that supports encryption.

Change-Id: I13b1d983356845f3ffc1945cedf53234218f32e5

2 files changed, 37 insertions, 0 deletions

diff --git a/util/errors.go b/util/errors.go
index aafeadd..bd63ac8 100644
--- a/util/errors.go
+++ b/util/errors.go
@@ -22,6 +22,7 @@ package util
 import (
 	"fmt"
 	"log"
+	"os"
 )
 
 // InvalidInputF creates an error that should indicate either bad input from a
@@ -48,3 +49,17 @@ func NeverError(err error) {
 		log.Panicf("NeverError() check failed: %v", err)
 	}
 }
+
+// UnderlyingError returns the underlying error for known os error types.
+// From: src/os/error.go
+func UnderlyingError(err error) error {
+	switch err := err.(type) {
+	case *os.PathError:
+		return err.Err
+	case *os.LinkError:
+		return err.Err
+	case *os.SyscallError:
+		return err.Err
+	}
+	return err
+}
diff --git a/util/util.go b/util/util.go
index 9439d0e..7574f35 100644
--- a/util/util.go
+++ b/util/util.go
@@ -31,3 +31,25 @@ import (
 func Ptr(slice []byte) unsafe.Pointer {
 	return unsafe.Pointer(&slice[0])
 }
+
+// Index returns the first index i such that inVal == inArray[i].
+// ok is true if we find a match, false otherwise.
+func Index(inVal int64, inArray []int64) (index int, ok bool) {
+	for index, val := range inArray {
+		if val == inVal {
+			return index, true
+		}
+	}
+	return 0, false
+}
+
+// Lookup finds inVal in inArray and returns the corresponding element in
+// outArray. Specifically, if inVal == inArray[i], outVal == outArray[i].
+// ok is true if we find a match, false otherwise.
+func Lookup(inVal int64, inArray, outArray []int64) (outVal int64, ok bool) {
+	index, ok := Index(inVal, inArray)
+	if !ok {
+		return 0, false
+	}
+	return outArray[index], true
+}