github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/sentry/syscalls/linux/sys_syslog.go (about)

     1  // Copyright 2018 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package linux
    16  
    17  import (
    18  	"github.com/SagerNet/gvisor/pkg/errors/linuxerr"
    19  	"github.com/SagerNet/gvisor/pkg/sentry/arch"
    20  	"github.com/SagerNet/gvisor/pkg/sentry/kernel"
    21  	"github.com/SagerNet/gvisor/pkg/syserror"
    22  )
    23  
    24  const (
    25  	_SYSLOG_ACTION_READ_ALL    = 3
    26  	_SYSLOG_ACTION_SIZE_BUFFER = 10
    27  )
    28  
    29  // logBufLen is the default syslog buffer size on Linux.
    30  const logBufLen = 1 << 17
    31  
    32  // Syslog implements part of Linux syscall syslog.
    33  //
    34  // Only the unpriviledged commands are implemented, allowing applications to
    35  // read a fun dmesg.
    36  func Syslog(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
    37  	command := args[0].Int()
    38  	buf := args[1].Pointer()
    39  	size := int(args[2].Int())
    40  
    41  	switch command {
    42  	case _SYSLOG_ACTION_READ_ALL:
    43  		if size < 0 {
    44  			return 0, nil, linuxerr.EINVAL
    45  		}
    46  		if size > logBufLen {
    47  			size = logBufLen
    48  		}
    49  
    50  		log := t.Kernel().Syslog().Log()
    51  		if len(log) > size {
    52  			log = log[:size]
    53  		}
    54  
    55  		n, err := t.CopyOutBytes(buf, log)
    56  		return uintptr(n), nil, err
    57  	case _SYSLOG_ACTION_SIZE_BUFFER:
    58  		return logBufLen, nil, nil
    59  	default:
    60  		return 0, nil, syserror.ENOSYS
    61  	}
    62  }