syscall: validate ParseDirent inputs

Don't panic, crash, or return references to uninitialized memory when
ParseDirent is passed invalid input.

Move common dirent parsing to syscall.go with minimal platform-specific
functions in syscall_$GOOS.go.

Fixes #15653

Change-Id: I5602475e02321fe381064488401c14b33bec6886
Reviewed-on: https://go-review.googlesource.com/23780
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/syscall/dirent.go

@@ -0,0 +1,102 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+
+package syscall
+
+import "unsafe"
+
+// readInt returns the size-bytes unsigned integer in native byte order at offset off.
+func readInt(b []byte, off, size uintptr) (u uint64, ok bool) {
+	if len(b) < int(off+size) {
+		return 0, false
+	}
+	if isBigEndian {
+		return readIntBE(b[off:], size), true
+	}
+	return readIntLE(b[off:], size), true
+}
+
+func readIntBE(b []byte, size uintptr) uint64 {
+	switch size {
+	case 1:
+		return uint64(b[0])
+	case 2:
+		_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[1]) | uint64(b[0])<<8
+	case 4:
+		_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[3]) | uint64(b[2])<<8 | uint64(b[1])<<16 | uint64(b[0])<<24
+	case 8:
+		_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
+			uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
+	default:
+		panic("syscall: readInt with unsupported size")
+	}
+}
+
+func readIntLE(b []byte, size uintptr) uint64 {
+	switch size {
+	case 1:
+		return uint64(b[0])
+	case 2:
+		_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[0]) | uint64(b[1])<<8
+	case 4:
+		_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24
+	case 8:
+		_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
+			uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
+	default:
+		panic("syscall: readInt with unsupported size")
+	}
+}
+
+// ParseDirent parses up to max directory entries in buf,
+// appending the names to names. It returns the number of
+// bytes consumed from buf, the number of entries added
+// to names, and the new names slice.
+func ParseDirent(buf []byte, max int, names []string) (consumed int, count int, newnames []string) {
+	origlen := len(buf)
+	count = 0
+	for max != 0 && len(buf) > 0 {
+		reclen, ok := direntReclen(buf)
+		if !ok || reclen > uint64(len(buf)) {
+			return origlen, count, names
+		}
+		rec := buf[:reclen]
+		buf = buf[reclen:]
+		ino, ok := direntIno(rec)
+		if !ok {
+			break
+		}
+		if ino == 0 { // File absent in directory.
+			continue
+		}
+		const namoff = uint64(unsafe.Offsetof(Dirent{}.Name))
+		namlen, ok := direntNamlen(rec)
+		if !ok || namoff+namlen > uint64(len(rec)) {
+			break
+		}
+		name := rec[namoff : namoff+namlen]
+		for i, c := range name {
+			if c == 0 {
+				name = name[:i]
+				break
+			}
+		}
+		// Check for useless names before allocating a string.
+		if string(name) == "." || string(name) == ".." {
+			continue
+		}
+		max--
+		count++
+		names = append(names, string(name))
+	}
+	return origlen - len(buf), count, names
+}

src/syscall/endian_big.go

@@ -0,0 +1,9 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+//
+// +build ppc64 s390x mips64
+
+package syscall
+
+const isBigEndian = true

src/syscall/endian_little.go

@@ -0,0 +1,9 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+//
+// +build 386 amd64 amd64p32 arm arm64 ppc64le mips64le
+
+package syscall
+
+const isBigEndian = false

src/syscall/syscall_darwin.go

@@ -75,32 +75,16 @@ func nametomib(name string) (mib []_C_int, err error) {
 	return buf[0 : n/siz], nil
 }
 
-// ParseDirent parses up to max directory entries in buf,
-// appending the names to names. It returns the number
-// bytes consumed from buf, the number of entries added
-// to names, and the new names slice.
-func ParseDirent(buf []byte, max int, names []string) (consumed int, count int, newnames []string) {
-	origlen := len(buf)
-	for max != 0 && len(buf) > 0 {
-		dirent := (*Dirent)(unsafe.Pointer(&buf[0]))
-		if dirent.Reclen == 0 {
-			buf = nil
-			break
+func direntIno(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Ino), unsafe.Sizeof(Dirent{}.Ino))
 }
-		buf = buf[dirent.Reclen:]
-		if dirent.Ino == 0 { // File absent in directory.
-			continue
+
+func direntReclen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Reclen), unsafe.Sizeof(Dirent{}.Reclen))
 }
-		bytes := (*[10000]byte)(unsafe.Pointer(&dirent.Name[0]))
-		var name = string(bytes[0:dirent.Namlen])
-		if name == "." || name == ".." { // Useless names
-			continue
-		}
-		max--
-		count++
-		names = append(names, name)
-	}
-	return origlen - len(buf), count, names
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Namlen), unsafe.Sizeof(Dirent{}.Namlen))
 }
 
 //sys   ptrace(request int, pid int, addr uintptr, data uintptr) (err error)

src/syscall/syscall_dragonfly.go

@@ -56,29 +56,20 @@ func nametomib(name string) (mib []_C_int, err error) {
 	return buf[0 : n/siz], nil
 }
 
-// ParseDirent parses up to max directory entries in buf,
-// appending the names to names. It returns the number
-// bytes consumed from buf, the number of entries added
-// to names, and the new names slice.
-func ParseDirent(buf []byte, max int, names []string) (consumed int, count int, newnames []string) {
-	origlen := len(buf)
-	for max != 0 && len(buf) > 0 {
-		dirent := (*Dirent)(unsafe.Pointer(&buf[0]))
-		reclen := int(16+dirent.Namlen+1+7) & ^7
-		buf = buf[reclen:]
-		if dirent.Fileno == 0 { // File absent in directory.
-			continue
+func direntIno(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Ino), unsafe.Sizeof(Dirent{}.Ino))
 }
-		bytes := (*[10000]byte)(unsafe.Pointer(&dirent.Name[0]))
-		var name = string(bytes[0:dirent.Namlen])
-		if name == "." || name == ".." { // Useless names
-			continue
+
+func direntReclen(buf []byte) (uint64, bool) {
+	namlen, ok := direntNamlen(buf)
+	if !ok {
+		return 0, false
 	}
-		max--
-		count++
-		names = append(names, name)
+	return (16 + namlen + 1 + 7) & ^7, true
 }
-	return origlen - len(buf), count, names
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Namlen), unsafe.Sizeof(Dirent{}.Namlen))
 }
 
 //sysnb pipe() (r int, w int, err error)

src/syscall/syscall_freebsd.go

@@ -54,32 +54,16 @@ func nametomib(name string) (mib []_C_int, err error) {
 	return buf[0 : n/siz], nil
 }
 
-// ParseDirent parses up to max directory entries in buf,
-// appending the names to names. It returns the number
-// bytes consumed from buf, the number of entries added
-// to names, and the new names slice.
-func ParseDirent(buf []byte, max int, names []string) (consumed int, count int, newnames []string) {
-	origlen := len(buf)
-	for max != 0 && len(buf) > 0 {
-		dirent := (*Dirent)(unsafe.Pointer(&buf[0]))
-		if dirent.Reclen == 0 {
-			buf = nil
-			break
+func direntIno(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Fileno), unsafe.Sizeof(Dirent{}.Fileno))
 }
-		buf = buf[dirent.Reclen:]
-		if dirent.Fileno == 0 { // File absent in directory.
-			continue
+
+func direntReclen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Reclen), unsafe.Sizeof(Dirent{}.Reclen))
 }
-		bytes := (*[10000]byte)(unsafe.Pointer(&dirent.Name[0]))
-		var name = string(bytes[0:dirent.Namlen])
-		if name == "." || name == ".." { // Useless names
-			continue
-		}
-		max--
-		count++
-		names = append(names, name)
-	}
-	return origlen - len(buf), count, names
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Namlen), unsafe.Sizeof(Dirent{}.Namlen))
 }
 
 //sysnb pipe() (r int, w int, err error)

src/syscall/syscall_linux.go

@@ -757,38 +757,24 @@ func Reboot(cmd int) (err error) {
 	return reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, cmd, "")
 }
 
-func clen(n []byte) int {
-	for i := 0; i < len(n); i++ {
-		if n[i] == 0 {
-			return i
-		}
-	}
-	return len(n)
-}
-
 func ReadDirent(fd int, buf []byte) (n int, err error) {
 	return Getdents(fd, buf)
 }
 
-func ParseDirent(buf []byte, max int, names []string) (consumed int, count int, newnames []string) {
-	origlen := len(buf)
-	count = 0
-	for max != 0 && len(buf) > 0 {
-		dirent := (*Dirent)(unsafe.Pointer(&buf[0]))
-		buf = buf[dirent.Reclen:]
-		if dirent.Ino == 0 { // File absent in directory.
-			continue
+func direntIno(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Ino), unsafe.Sizeof(Dirent{}.Ino))
 }
-		bytes := (*[10000]byte)(unsafe.Pointer(&dirent.Name[0]))
-		var name = string(bytes[0:clen(bytes[:])])
-		if name == "." || name == ".." { // Useless names
-			continue
+
+func direntReclen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Reclen), unsafe.Sizeof(Dirent{}.Reclen))
 }
-		max--
-		count++
-		names = append(names, name)
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	reclen, ok := direntReclen(buf)
+	if !ok {
+		return 0, false
 	}
-	return origlen - len(buf), count, names
+	return reclen - uint64(unsafe.Offsetof(Dirent{}.Name)), true
 }
 
 //sys	mount(source string, target string, fstype string, flags uintptr, data *byte) (err error)

src/syscall/syscall_nacl.go

@@ -26,34 +26,20 @@ type Dirent struct {
 	Name   [256]byte
 }
 
-func ParseDirent(buf []byte, max int, names []string) (consumed int, count int, newnames []string) {
-	origlen := len(buf)
-	count = 0
-	for max != 0 && len(buf) > 0 {
-		dirent := (*Dirent)(unsafe.Pointer(&buf[0]))
-		buf = buf[dirent.Reclen:]
-		if dirent.Ino == 0 { // File absent in directory.
-			continue
-		}
-		bytes := (*[512 + PathMax]byte)(unsafe.Pointer(&dirent.Name[0]))
-		var name = string(bytes[0:clen(bytes[:])])
-		if name == "." || name == ".." { // Useless names
-			continue
-		}
-		max--
-		count++
-		names = append(names, name)
-	}
-	return origlen - len(buf), count, names
+func direntIno(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Ino), unsafe.Sizeof(Dirent{}.Ino))
 }
 
-func clen(n []byte) int {
-	for i := 0; i < len(n); i++ {
-		if n[i] == 0 {
-			return i
+func direntReclen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Reclen), unsafe.Sizeof(Dirent{}.Reclen))
 }
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	reclen, ok := direntReclen(buf)
+	if !ok {
+		return 0, false
 	}
-	return len(n)
+	return reclen - uint64(unsafe.Offsetof(Dirent{}.Name)), true
 }
 
 const PathMax = 256

src/syscall/syscall_netbsd.go

@@ -90,32 +90,16 @@ func nametomib(name string) (mib []_C_int, err error) {
 	return mib, nil
 }
 
-// ParseDirent parses up to max directory entries in buf,
-// appending the names to names. It returns the number
-// bytes consumed from buf, the number of entries added
-// to names, and the new names slice.
-func ParseDirent(buf []byte, max int, names []string) (consumed int, count int, newnames []string) {
-	origlen := len(buf)
-	for max != 0 && len(buf) > 0 {
-		dirent := (*Dirent)(unsafe.Pointer(&buf[0]))
-		if dirent.Reclen == 0 {
-			buf = nil
-			break
+func direntIno(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Fileno), unsafe.Sizeof(Dirent{}.Fileno))
 }
-		buf = buf[dirent.Reclen:]
-		if dirent.Fileno == 0 { // File absent in directory.
-			continue
+
+func direntReclen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Reclen), unsafe.Sizeof(Dirent{}.Reclen))
 }
-		bytes := (*[10000]byte)(unsafe.Pointer(&dirent.Name[0]))
-		var name = string(bytes[0:dirent.Namlen])
-		if name == "." || name == ".." { // Useless names
-			continue
-		}
-		max--
-		count++
-		names = append(names, name)
-	}
-	return origlen - len(buf), count, names
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Namlen), unsafe.Sizeof(Dirent{}.Namlen))
 }
 
 //sysnb pipe() (fd1 int, fd2 int, err error)

src/syscall/syscall_openbsd.go

@@ -50,32 +50,16 @@ func nametomib(name string) (mib []_C_int, err error) {
 	return nil, EINVAL
 }
 
-// ParseDirent parses up to max directory entries in buf,
-// appending the names to names. It returns the number
-// bytes consumed from buf, the number of entries added
-// to names, and the new names slice.
-func ParseDirent(buf []byte, max int, names []string) (consumed int, count int, newnames []string) {
-	origlen := len(buf)
-	for max != 0 && len(buf) > 0 {
-		dirent := (*Dirent)(unsafe.Pointer(&buf[0]))
-		if dirent.Reclen == 0 {
-			buf = nil
-			break
+func direntIno(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Fileno), unsafe.Sizeof(Dirent{}.Fileno))
 }
-		buf = buf[dirent.Reclen:]
-		if dirent.Fileno == 0 { // File absent in directory.
-			continue
+
+func direntReclen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Reclen), unsafe.Sizeof(Dirent{}.Reclen))
 }
-		bytes := (*[10000]byte)(unsafe.Pointer(&dirent.Name[0]))
-		var name = string(bytes[0:dirent.Namlen])
-		if name == "." || name == ".." { // Useless names
-			continue
-		}
-		max--
-		count++
-		names = append(names, name)
-	}
-	return origlen - len(buf), count, names
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Namlen), unsafe.Sizeof(Dirent{}.Namlen))
 }
 
 //sysnb pipe(p *[2]_C_int) (err error)

src/syscall/syscall_solaris.go

@@ -38,32 +38,20 @@ func clen(n []byte) int {
 	return len(n)
 }
 
-// ParseDirent parses up to max directory entries in buf,
-// appending the names to names. It returns the number
-// bytes consumed from buf, the number of entries added
-// to names, and the new names slice.
-func ParseDirent(buf []byte, max int, names []string) (consumed int, count int, newnames []string) {
-	origlen := len(buf)
-	for max != 0 && len(buf) > 0 {
-		dirent := (*Dirent)(unsafe.Pointer(&buf[0]))
-		if dirent.Reclen == 0 {
-			buf = nil
-			break
+func direntIno(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Ino), unsafe.Sizeof(Dirent{}.Ino))
 }
-		buf = buf[dirent.Reclen:]
-		if dirent.Ino == 0 { // File absent in directory.
-			continue
+
+func direntReclen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(Dirent{}.Reclen), unsafe.Sizeof(Dirent{}.Reclen))
 }
-		bytes := (*[10000]byte)(unsafe.Pointer(&dirent.Name[0]))
-		var name = string(bytes[0:clen(bytes[:])])
-		if name == "." || name == ".." { // Useless names
-			continue
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	reclen, ok := direntReclen(buf)
+	if !ok {
+		return 0, false
 	}
-		max--
-		count++
-		names = append(names, name)
-	}
-	return origlen - len(buf), count, names
+	return reclen - uint64(unsafe.Offsetof(Dirent{}.Name)), true
 }
 
 func pipe() (r uintptr, w uintptr, err uintptr)