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// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
// See License.txt for license information.
package sandbox
import (
"syscall"
"unsafe"
"github.com/pkg/errors"
"golang.org/x/net/bpf"
"golang.org/x/sys/unix"
)
const (
SECCOMP_RET_ALLOW = 0x7fff0000
SECCOMP_RET_ERRNO = 0x00050000
)
const (
EM_X86_64 = 62
__AUDIT_ARCH_64BIT = 0x80000000
__AUDIT_ARCH_LE = 0x40000000
AUDIT_ARCH_X86_64 = EM_X86_64 | __AUDIT_ARCH_64BIT | __AUDIT_ARCH_LE
nrSize = 4
archOffset = nrSize
ipOffset = archOffset + 4
argsOffset = ipOffset + 8
)
type SeccompCondition interface {
Filter(littleEndian bool, skipFalseSentinel uint8) []bpf.Instruction
}
func seccompArgLowWord(arg int, littleEndian bool) uint32 {
offset := uint32(argsOffset + arg*8)
if !littleEndian {
offset += 4
}
return offset
}
func seccompArgHighWord(arg int, littleEndian bool) uint32 {
offset := uint32(argsOffset + arg*8)
if littleEndian {
offset += 4
}
return offset
}
type SeccompArgHasNoBits struct {
Arg int
Mask uint64
}
func (c SeccompArgHasNoBits) Filter(littleEndian bool, skipFalseSentinel uint8) []bpf.Instruction {
return []bpf.Instruction{
bpf.LoadAbsolute{Off: seccompArgHighWord(c.Arg, littleEndian), Size: 4},
bpf.JumpIf{Cond: bpf.JumpBitsSet, Val: uint32(c.Mask >> 32), SkipTrue: skipFalseSentinel},
bpf.LoadAbsolute{Off: seccompArgLowWord(c.Arg, littleEndian), Size: 4},
bpf.JumpIf{Cond: bpf.JumpBitsSet, Val: uint32(c.Mask), SkipTrue: skipFalseSentinel},
}
}
type SeccompArgHasAnyBit struct {
Arg int
Mask uint64
}
func (c SeccompArgHasAnyBit) Filter(littleEndian bool, skipFalseSentinel uint8) []bpf.Instruction {
return []bpf.Instruction{
bpf.LoadAbsolute{Off: seccompArgHighWord(c.Arg, littleEndian), Size: 4},
bpf.JumpIf{Cond: bpf.JumpBitsSet, Val: uint32(c.Mask >> 32), SkipTrue: 2},
bpf.LoadAbsolute{Off: seccompArgLowWord(c.Arg, littleEndian), Size: 4},
bpf.JumpIf{Cond: bpf.JumpBitsSet, Val: uint32(c.Mask), SkipFalse: skipFalseSentinel},
}
}
type SeccompArgEquals struct {
Arg int
Value uint64
}
func (c SeccompArgEquals) Filter(littleEndian bool, skipFalseSentinel uint8) []bpf.Instruction {
return []bpf.Instruction{
bpf.LoadAbsolute{Off: seccompArgHighWord(c.Arg, littleEndian), Size: 4},
bpf.JumpIf{Cond: bpf.JumpEqual, Val: uint32(c.Value >> 32), SkipFalse: skipFalseSentinel},
bpf.LoadAbsolute{Off: seccompArgLowWord(c.Arg, littleEndian), Size: 4},
bpf.JumpIf{Cond: bpf.JumpEqual, Val: uint32(c.Value), SkipFalse: skipFalseSentinel},
}
}
type SeccompConditions struct {
All []SeccompCondition
}
type SeccompSyscall struct {
Syscall uint32
Any []SeccompConditions
}
func SeccompFilter(arch uint32, allowedSyscalls []SeccompSyscall) (filter []bpf.Instruction) {
filter = append(filter,
bpf.LoadAbsolute{Off: archOffset, Size: 4},
bpf.JumpIf{Cond: bpf.JumpEqual, Val: arch, SkipTrue: 1},
bpf.RetConstant{Val: uint32(SECCOMP_RET_ERRNO | unix.EPERM)},
)
filter = append(filter, bpf.LoadAbsolute{Off: 0, Size: nrSize})
for _, s := range allowedSyscalls {
if s.Any != nil {
syscallStart := len(filter)
filter = append(filter, bpf.Instruction(nil))
for _, cs := range s.Any {
anyStart := len(filter)
for _, c := range cs.All {
filter = append(filter, c.Filter((arch&__AUDIT_ARCH_LE) != 0, 255)...)
}
filter = append(filter, bpf.RetConstant{Val: SECCOMP_RET_ALLOW})
for i := anyStart; i < len(filter); i++ {
if jump, ok := filter[i].(bpf.JumpIf); ok {
if len(filter)-i-1 > 255 {
panic("condition too long")
}
if jump.SkipFalse == 255 {
jump.SkipFalse = uint8(len(filter) - i - 1)
}
if jump.SkipTrue == 255 {
jump.SkipTrue = uint8(len(filter) - i - 1)
}
filter[i] = jump
}
}
}
filter = append(filter, bpf.RetConstant{Val: uint32(SECCOMP_RET_ERRNO | unix.EPERM)})
if len(filter)-syscallStart-1 > 255 {
panic("conditions too long")
}
filter[syscallStart] = bpf.JumpIf{Cond: bpf.JumpEqual, Val: uint32(s.Syscall), SkipFalse: uint8(len(filter) - syscallStart - 1)}
} else {
filter = append(filter,
bpf.JumpIf{Cond: bpf.JumpEqual, Val: uint32(s.Syscall), SkipFalse: 1},
bpf.RetConstant{Val: SECCOMP_RET_ALLOW},
)
}
}
return append(filter, bpf.RetConstant{Val: uint32(SECCOMP_RET_ERRNO | unix.EPERM)})
}
func EnableSeccompFilter(filter []bpf.Instruction) error {
assembled, err := bpf.Assemble(filter)
if err != nil {
return errors.Wrapf(err, "unable to assemble filter")
}
sockFilter := make([]unix.SockFilter, len(filter))
for i, instruction := range assembled {
sockFilter[i].Code = instruction.Op
sockFilter[i].Jt = instruction.Jt
sockFilter[i].Jf = instruction.Jf
sockFilter[i].K = instruction.K
}
prog := unix.SockFprog{
Len: uint16(len(sockFilter)),
Filter: &sockFilter[0],
}
if _, _, errno := syscall.Syscall(syscall.SYS_PRCTL, unix.PR_SET_SECCOMP, unix.SECCOMP_MODE_FILTER, uintptr(unsafe.Pointer(&prog))); errno != 0 {
return errors.Wrapf(syscall.Errno(errno), "syscall error")
}
return nil
}
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