unix: require minimum OpenBSD 6.4 for pledge, unveil

OpenBSD 7.3 and 7.4 are the only supported OpenBSD releases.  This change simplifies the version detection and error handling to require at least OpenBSD 6.4 to call the Pledge and Unveil functions.

Updates golang/go#63569.

Change-Id: I6bd0d58807a73a532ddd2d3239687ca19a93db9d
GitHub-Last-Rev: d03d157e76
GitHub-Pull-Request: golang/sys#177
Reviewed-on: https://go-review.googlesource.com/c/sys/+/537355
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Joel Sing <joel@sing.id.au>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Joel Sing <joel@sing.id.au>

unix/pledge_openbsd.go

@@ -14,21 +14,13 @@ import (
 
 // Pledge implements the pledge syscall.
 //
-// The pledge syscall does not accept execpromises on OpenBSD releases
-// before 6.3.
-//
-// execpromises must be empty when Pledge is called on OpenBSD
-// releases predating 6.3, otherwise an error will be returned.
+// This changes both the promises and execpromises; use PledgePromises or
+// PledgeExecpromises to only change the promises or execpromises
+// respectively.
 //
 // For more information see pledge(2).
 func Pledge(promises, execpromises string) error {
-	maj, min, err := majmin()
-	if err != nil {
-		return err
-	}
-
-	err = pledgeAvailable(maj, min, execpromises)
-	if err != nil {
+	if err := pledgeAvailable(); err != nil {
 		return err
 	}
 
@@ -37,20 +29,13 @@ func Pledge(promises, execpromises string) error {
 		return err
 	}
 
-	// This variable will hold either a nil unsafe.Pointer or
-	// an unsafe.Pointer to a string (execpromises).
-	var expr unsafe.Pointer
-
-	// If we're running on OpenBSD > 6.2, pass execpromises to the syscall.
-	if maj > 6 || (maj == 6 && min > 2) {
-		exptr, err := syscall.BytePtrFromString(execpromises)
-		if err != nil {
-			return err
-		}
-		expr = unsafe.Pointer(exptr)
+	exptr, err := syscall.BytePtrFromString(execpromises)
+	if err != nil {
+		return err
 	}
 
-	_, _, e := syscall.Syscall(SYS_PLEDGE, uintptr(unsafe.Pointer(pptr)), uintptr(expr), 0)
+	_, _, e := syscall.Syscall(SYS_PLEDGE, uintptr(unsafe.Pointer(pptr)),
+		uintptr(unsafe.Pointer(exptr)), 0)
 	if e != 0 {
 		return e
 	}
@@ -64,13 +49,7 @@ func Pledge(promises, execpromises string) error {
 //
 // For more information see pledge(2).
 func PledgePromises(promises string) error {
-	maj, min, err := majmin()
-	if err != nil {
-		return err
-	}
-
-	err = pledgeAvailable(maj, min, "")
-	if err != nil {
+	if err := pledgeAvailable(); err != nil {
 		return err
 	}
 
@@ -82,7 +61,8 @@ func PledgePromises(promises string) error {
 		return err
 	}
 
-	_, _, e := syscall.Syscall(SYS_PLEDGE, uintptr(unsafe.Pointer(pptr)), uintptr(expr), 0)
+	_, _, e := syscall.Syscall(SYS_PLEDGE, uintptr(unsafe.Pointer(pptr)),
+		uintptr(expr), 0)
 	if e != 0 {
 		return e
 	}
@@ -96,13 +76,7 @@ func PledgePromises(promises string) error {
 //
 // For more information see pledge(2).
 func PledgeExecpromises(execpromises string) error {
-	maj, min, err := majmin()
-	if err != nil {
-		return err
-	}
-
-	err = pledgeAvailable(maj, min, execpromises)
-	if err != nil {
+	if err := pledgeAvailable(); err != nil {
 		return err
 	}
 
@@ -114,7 +88,8 @@ func PledgeExecpromises(execpromises string) error {
 		return err
 	}
 
-	_, _, e := syscall.Syscall(SYS_PLEDGE, uintptr(pptr), uintptr(unsafe.Pointer(exptr)), 0)
+	_, _, e := syscall.Syscall(SYS_PLEDGE, uintptr(pptr),
+		uintptr(unsafe.Pointer(exptr)), 0)
 	if e != 0 {
 		return e
 	}
@@ -147,16 +122,15 @@ func majmin() (major int, minor int, err error) {
 
 // pledgeAvailable checks for availability of the pledge(2) syscall
 // based on the running OpenBSD version.
-func pledgeAvailable(maj, min int, execpromises string) error {
-	// If OpenBSD <= 5.9, pledge is not available.
-	if (maj == 5 && min != 9) || maj < 5 {
-		return fmt.Errorf("pledge syscall is not available on OpenBSD %d.%d", maj, min)
+func pledgeAvailable() error {
+	maj, min, err := majmin()
+	if err != nil {
+		return err
 	}
 
-	// If OpenBSD <= 6.2 and execpromises is not empty,
-	// return an error - execpromises is not available before 6.3
-	if (maj < 6 || (maj == 6 && min <= 2)) && execpromises != "" {
-		return fmt.Errorf("cannot use execpromises on OpenBSD %d.%d", maj, min)
+	// Require OpenBSD 6.4 as a minimum.
+	if maj < 6 || (maj == 6 && min <= 3) {
+		return fmt.Errorf("cannot call Pledge on OpenBSD %d.%d", maj, min)
 	}
 
 	return nil

unix/unveil_openbsd.go

@@ -5,6 +5,7 @@
 package unix
 
 import (
+	"fmt"
 	"syscall"
 	"unsafe"
 )
@@ -14,6 +15,9 @@ import (
 // Note that the special case of blocking further
 // unveil calls is handled by UnveilBlock.
 func Unveil(path string, flags string) error {
+	if err := supportsUnveil(); err != nil {
+		return err
+	}
 	pathPtr, err := syscall.BytePtrFromString(path)
 	if err != nil {
 		return err
@@ -32,6 +36,9 @@ func Unveil(path string, flags string) error {
 // UnveilBlock blocks future unveil calls.
 // For more information see unveil(2).
 func UnveilBlock() error {
+	if err := supportsUnveil(); err != nil {
+		return err
+	}
 	// Both pointers must be nil.
 	var pathUnsafe, flagsUnsafe unsafe.Pointer
 	_, _, e := syscall.Syscall(SYS_UNVEIL, uintptr(pathUnsafe), uintptr(flagsUnsafe), 0)
@@ -40,3 +47,19 @@ func UnveilBlock() error {
 	}
 	return nil
 }
+
+// supportsUnveil checks for availability of the unveil(2) system call based
+// on the running OpenBSD version.
+func supportsUnveil() error {
+	maj, min, err := majmin()
+	if err != nil {
+		return err
+	}
+
+	// unveil is not available before 6.4
+	if maj < 6 || (maj == 6 && min <= 3) {
+		return fmt.Errorf("cannot call Unveil on OpenBSD %d.%d", maj, min)
+	}
+
+	return nil
+}