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