1 files changed, 92 insertions, 0 deletions
diff --git a/pkg/sentry/syscalls/linux/sys_random.go b/pkg/sentry/syscalls/linux/sys_random.go
new file mode 100644
index 000000000..2dd59b1c3
--- /dev/null
+++ b/pkg/sentry/syscalls/linux/sys_random.go
@@ -0,0 +1,92 @@
+// Copyright 2018 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package linux
+
+import (
+	"crypto/rand"
+	"io"
+	"math"
+
+	"gvisor.googlesource.com/gvisor/pkg/sentry/arch"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/safemem"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
+	"gvisor.googlesource.com/gvisor/pkg/syserror"
+)
+
+const (
+	_GRND_NONBLOCK = 0x1
+	_GRND_RANDOM   = 0x2
+)
+
+// GetRandom implements the linux syscall getrandom(2).
+//
+// In a multi-tenant/shared environment, the only valid implementation is to
+// fetch data from the urandom pool, otherwise starvation attacks become
+// possible. The urandom pool is also expected to have plenty of entropy, thus
+// the GRND_RANDOM flag is ignored. The GRND_NONBLOCK flag does not apply, as
+// the pool will already be initialized.
+func GetRandom(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	addr := args[0].Pointer()
+	length := args[1].SizeT()
+	flags := args[2].Int()
+
+	// Flags are checked for validity but otherwise ignored. See above.
+	if flags & ^(_GRND_NONBLOCK|_GRND_RANDOM) != 0 {
+		return 0, nil, syserror.EINVAL
+	}
+
+	if length > math.MaxInt32 {
+		length = math.MaxInt32
+	}
+	ar, ok := addr.ToRange(uint64(length))
+	if !ok {
+		return 0, nil, syserror.EFAULT
+	}
+
+	// "If the urandom source has been initialized, reads of up to 256 bytes
+	// will always return as many bytes as requested and will not be
+	// interrupted by signals. No such guarantees apply for larger buffer
+	// sizes." - getrandom(2)
+	min := int(length)
+	if min > 256 {
+		min = 256
+	}
+	n, err := t.MemoryManager().CopyOutFrom(t, usermem.AddrRangeSeqOf(ar), safemem.FromIOReader{&randReader{-1, min}}, usermem.IOOpts{
+		AddressSpaceActive: true,
+	})
+	if n >= int64(min) {
+		return uintptr(n), nil, nil
+	}
+	return 0, nil, err
+}
+
+// randReader is a io.Reader that handles partial reads from rand.Reader.
+type randReader struct {
+	done int
+	min  int
+}
+
+// Read implements io.Reader.Read.
+func (r *randReader) Read(dst []byte) (int, error) {
+	if r.done >= r.min {
+		return rand.Reader.Read(dst)
+	}
+	min := r.min - r.done
+	if min > len(dst) {
+		min = len(dst)
+	}
+	return io.ReadAtLeast(rand.Reader, dst, min)
+}