cmd/fscrypt: Add --user flag for running as root

The --user flag can now be used to have the targe user (the one whose
keyring and password will be used in fscrypt) be different than the
calling user. Very usefull for things like

	sudo fscrypt purge /media/joerichey/usb --user=joerichey

which will now have privileges to drop caches, but will properly clear
the keys from the user's keyring.

1 files changed, 43 insertions, 27 deletions

diff --git a/cmd/fscrypt/commands.go b/cmd/fscrypt/commands.go
index 3e8bc98..43c9cb0 100644
--- a/cmd/fscrypt/commands.go
+++ b/cmd/fscrypt/commands.go
@@ -25,8 +25,6 @@ import (
 	"log"
 	"os"
 
-	"golang.org/x/sys/unix"
-
 	"github.com/pkg/errors"
 	"github.com/urfave/cli"
 
@@ -34,6 +32,7 @@ import (
 	"github.com/google/fscrypt/filesystem"
 	"github.com/google/fscrypt/metadata"
 	"github.com/google/fscrypt/security"
+	"github.com/google/fscrypt/util"
 )
 
 // Setup is a command which can to global or per-filesystem initialization.
@@ -60,7 +59,6 @@ var Setup = cli.Command{
 
 func setupAction(c *cli.Context) error {
 	var err error
-
 	switch c.NArg() {
 	case 0:
 		// Case (1) - global setup
@@ -92,7 +90,7 @@ var Encrypt = cli.Command{
 		immediately be used.`, directoryArg, shortDisplay(policyFlag),
 		shortDisplay(protectorFlag), mountpointArg),
 	Flags: []cli.Flag{policyFlag, unlockWithFlag, protectorFlag, sourceFlag,
-		nameFlag, keyFileFlag, skipUnlockFlag},
+		userFlag, nameFlag, keyFileFlag, skipUnlockFlag},
 	Action: encryptAction,
 }
 
@@ -121,7 +119,11 @@ func encryptAction(c *cli.Context) error {
 // keyring unless --skip-unlock is used. On failure, an error is returned, any
 // metadata creation is reverted, and the directory is unmodified.
 func encryptPath(path string) (err error) {
-	ctx, err := actions.NewContextFromPath(path)
+	target, err := parseUserFlag()
+	if err != nil {
+		return
+	}
+	ctx, err := actions.NewContextFromPath(path, target)
 	if err != nil {
 		return
 	}
@@ -133,7 +135,7 @@ func encryptPath(path string) (err error) {
 	if policyFlag.Value != "" {
 		log.Printf("getting policy for %q", path)
 
-		policy, err = getPolicyFromFlag(policyFlag.Value)
+		policy, err = getPolicyFromFlag(policyFlag.Value, ctx.TargetUser)
 	} else {
 		log.Printf("creating policy for %q", path)
 
@@ -220,7 +222,7 @@ func checkEncryptable(ctx *actions.Context, path string) error {
 // created a new protector.
 func selectOrCreateProtector(ctx *actions.Context) (*actions.Protector, bool, error) {
 	if protectorFlag.Value != "" {
-		protector, err := getProtectorFromFlag(protectorFlag.Value)
+		protector, err := getProtectorFromFlag(protectorFlag.Value, ctx.TargetUser)
 		return protector, false, err
 	}
 
@@ -263,7 +265,7 @@ var Unlock = cli.Command{
 		locked again upon reboot, or after running "fscrypt purge" and
 		unmounting the corresponding filesystem.`, directoryArg,
 		shortDisplay(unlockWithFlag)),
-	Flags:  []cli.Flag{unlockWithFlag, keyFileFlag},
+	Flags:  []cli.Flag{unlockWithFlag, keyFileFlag, userFlag},
 	Action: unlockAction,
 }
 
@@ -272,8 +274,12 @@ func unlockAction(c *cli.Context) error {
 		return expectedArgsErr(c, 1, false)
 	}
 
+	target, err := parseUserFlag()
+	if err != nil {
+		return newExitError(c, err)
+	}
 	path := c.Args().Get(0)
-	ctx, err := actions.NewContextFromPath(path)
+	ctx, err := actions.NewContextFromPath(path, target)
 	if err != nil {
 		return newExitError(c, err)
 	}
@@ -336,7 +342,7 @@ var Purge = cli.Command{
 		can be eliminated by cycling the power or mitigated by using
 		page cache and slab cache poisoning.`, mountpointArg,
 		shortDisplay(dropCachesFlag)),
-	Flags:  []cli.Flag{forceFlag, dropCachesFlag},
+	Flags:  []cli.Flag{forceFlag, dropCachesFlag, userFlag},
 	Action: purgeAction,
 }
 
@@ -346,12 +352,17 @@ func purgeAction(c *cli.Context) error {
 	}
 
 	if dropCachesFlag.Value {
-		if unix.Geteuid() != 0 {
+		if !util.IsUserRoot() {
 			return newExitError(c, ErrDropCachesPerm)
 		}
 	}
 
-	ctx, err := actions.NewContextFromMountpoint(c.Args().Get(0))
+	target, err := parseUserFlag()
+	if err != nil {
+		return newExitError(c, err)
+	}
+	mountpoint := c.Args().Get(0)
+	ctx, err := actions.NewContextFromMountpoint(mountpoint, target)
 	if err != nil {
 		return newExitError(c, err)
 	}
@@ -417,7 +428,7 @@ func statusAction(c *cli.Context) error {
 		err = writeGlobalStatus(c.App.Writer)
 	case 1:
 		path := c.Args().Get(0)
-		ctx, mntErr := actions.NewContextFromMountpoint(path)
+		ctx, mntErr := actions.NewContextFromMountpoint(path, nil)
 
 		switch errors.Cause(mntErr) {
 		case nil:
@@ -487,7 +498,7 @@ var createProtector = cli.Command{
 		applicable). As with "fscrypt encrypt", these prompts can be
 		disabled with the appropriate flags.`, mountpointArg,
 		shortDisplay(protectorFlag)),
-	Flags:  []cli.Flag{sourceFlag, nameFlag, keyFileFlag},
+	Flags:  []cli.Flag{sourceFlag, nameFlag, keyFileFlag, userFlag},
 	Action: createProtectorAction,
 }
 
@@ -496,7 +507,12 @@ func createProtectorAction(c *cli.Context) error {
 		return expectedArgsErr(c, 1, false)
 	}
 
-	ctx, err := actions.NewContextFromMountpoint(c.Args().Get(0))
+	target, err := parseUserFlag()
+	if err != nil {
+		return newExitError(c, err)
+	}
+	mountpoint := c.Args().Get(0)
+	ctx, err := actions.NewContextFromMountpoint(mountpoint, target)
 	if err != nil {
 		return newExitError(c, err)
 	}
@@ -539,7 +555,7 @@ func createPolicyAction(c *cli.Context) error {
 		return expectedArgsErr(c, 1, false)
 	}
 
-	ctx, err := actions.NewContextFromMountpoint(c.Args().Get(0))
+	ctx, err := actions.NewContextFromMountpoint(c.Args().Get(0), nil)
 	if err != nil {
 		return newExitError(c, err)
 	}
@@ -547,7 +563,7 @@ func createPolicyAction(c *cli.Context) error {
 	if err := checkRequiredFlags(c, []*stringFlag{protectorFlag}); err != nil {
 		return err
 	}
-	protector, err := getProtectorFromFlag(protectorFlag.Value)
+	protector, err := getProtectorFromFlag(protectorFlag.Value, ctx.TargetUser)
 	if err != nil {
 		return newExitError(c, err)
 	}
@@ -608,7 +624,7 @@ func destoryMetadataAction(c *cli.Context) error {
 		switch {
 		case protectorFlag.Value != "":
 			// Case (1) - protector destroy
-			protector, err := getProtectorFromFlag(protectorFlag.Value)
+			protector, err := getProtectorFromFlag(protectorFlag.Value, nil)
 			if err != nil {
 				return newExitError(c, err)
 			}
@@ -627,7 +643,7 @@ func destoryMetadataAction(c *cli.Context) error {
 				protector.Descriptor(), protector.Context.Mount.Path)
 		case policyFlag.Value != "":
 			// Case (2) - policy destroy
-			policy, err := getPolicyFromFlag(policyFlag.Value)
+			policy, err := getPolicyFromFlag(policyFlag.Value, nil)
 			if err != nil {
 				return newExitError(c, err)
 			}
@@ -654,7 +670,7 @@ func destoryMetadataAction(c *cli.Context) error {
 	case 1:
 		// Case (3) - mountpoint destroy
 		path := c.Args().Get(0)
-		ctx, err := actions.NewContextFromMountpoint(path)
+		ctx, err := actions.NewContextFromMountpoint(path, nil)
 		if err != nil {
 			return newExitError(c, err)
 		}
@@ -694,7 +710,7 @@ func changePassphraseAction(c *cli.Context) error {
 		return err
 	}
 
-	protector, err := getProtectorFromFlag(protectorFlag.Value)
+	protector, err := getProtectorFromFlag(protectorFlag.Value, nil)
 	if err != nil {
 		return newExitError(c, err)
 	}
@@ -732,11 +748,11 @@ func addProtectorAction(c *cli.Context) error {
 		return err
 	}
 
-	protector, err := getProtectorFromFlag(protectorFlag.Value)
+	protector, err := getProtectorFromFlag(protectorFlag.Value, nil)
 	if err != nil {
 		return newExitError(c, err)
 	}
-	policy, err := getPolicyFromFlag(policyFlag.Value)
+	policy, err := getPolicyFromFlag(policyFlag.Value, protector.Context.TargetUser)
 	if err != nil {
 		return newExitError(c, err)
 	}
@@ -790,11 +806,11 @@ func removeProtectorAction(c *cli.Context) error {
 	}
 
 	// We do not need to unlock anything for this operation
-	protector, err := getProtectorFromFlag(protectorFlag.Value)
+	protector, err := getProtectorFromFlag(protectorFlag.Value, nil)
 	if err != nil {
 		return newExitError(c, err)
 	}
-	policy, err := getPolicyFromFlag(policyFlag.Value)
+	policy, err := getPolicyFromFlag(policyFlag.Value, protector.Context.TargetUser)
 	if err != nil {
 		return newExitError(c, err)
 	}
@@ -834,14 +850,14 @@ func dumpMetadataAction(c *cli.Context) error {
 	switch {
 	case protectorFlag.Value != "":
 		// Case (1) - protector print
-		protector, err := getProtectorFromFlag(protectorFlag.Value)
+		protector, err := getProtectorFromFlag(protectorFlag.Value, nil)
 		if err != nil {
 			return newExitError(c, err)
 		}
 		fmt.Fprintln(c.App.Writer, protector)
 	case policyFlag.Value != "":
 		// Case (2) - policy print
-		policy, err := getPolicyFromFlag(policyFlag.Value)
+		policy, err := getPolicyFromFlag(policyFlag.Value, nil)
 		if err != nil {
 			return newExitError(c, err)
 		}