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// Copyright 2020 The gVisor Authors.
//
// 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 (
"fmt"
"gvisor.dev/gvisor/pkg/errors/linuxerr"
"gvisor.dev/gvisor/pkg/hostarch"
"gvisor.dev/gvisor/pkg/sentry/arch"
"gvisor.dev/gvisor/pkg/sentry/kernel"
"gvisor.dev/gvisor/pkg/sentry/vfs"
"gvisor.dev/gvisor/pkg/sync"
"gvisor.dev/gvisor/pkg/usermem"
)
// Getdents implements Linux syscall getdents(2).
func Getdents(t *kernel.Task, sysno uintptr, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
return getdents(t, args, false /* isGetdents64 */)
}
// Getdents64 implements Linux syscall getdents64(2).
func Getdents64(t *kernel.Task, sysno uintptr, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
return getdents(t, args, true /* isGetdents64 */)
}
// DirentStructBytesWithoutName is enough to fit (struct linux_dirent) and
// (struct linux_dirent64) without accounting for the name parameter.
const DirentStructBytesWithoutName = 8 + 8 + 2 + 1 + 1
func getdents(t *kernel.Task, args arch.SyscallArguments, isGetdents64 bool) (uintptr, *kernel.SyscallControl, error) {
fd := args[0].Int()
addr := args[1].Pointer()
size := args[2].Int()
if size < DirentStructBytesWithoutName {
return 0, nil, linuxerr.EINVAL
}
file := t.GetFile(fd)
if file == nil {
return 0, nil, linuxerr.EBADF
}
defer file.DecRef(t)
// We want to be sure of the allowed buffer size before calling IterDirents,
// because this function depends on IterDirents saving state of which dirent
// was the last one that was successfully operated on.
allowedSize, err := t.MemoryManager().EnsurePMAsExist(t, addr, int64(size), usermem.IOOpts{
AddressSpaceActive: true,
})
if allowedSize == 0 {
return 0, nil, err
}
cb := getGetdentsCallback(t, int(allowedSize), int(size), isGetdents64)
err = file.IterDirents(t, cb)
n, _ := t.CopyOutBytes(addr, cb.buf[:cb.copied])
putGetdentsCallback(cb)
// Only report an error in case we didn't copy anything.
// If we did manage to give _something_ to the caller then the correct
// behaviour is to return success.
if n == 0 {
return 0, nil, err
}
return uintptr(n), nil, nil
}
type getdentsCallback struct {
t *kernel.Task
buf []byte
copied int
userReportedSize int
isGetdents64 bool
}
var getdentsCallbackPool = sync.Pool{
New: func() any {
return &getdentsCallback{}
},
}
func getGetdentsCallback(t *kernel.Task, size int, userReportedSize int, isGetdents64 bool) *getdentsCallback {
cb := getdentsCallbackPool.Get().(*getdentsCallback)
buf := cb.buf
if cap(buf) < size {
buf = make([]byte, size)
} else {
buf = buf[:size]
}
*cb = getdentsCallback{
t: t,
buf: buf,
copied: 0,
userReportedSize: userReportedSize,
isGetdents64: isGetdents64,
}
return cb
}
func putGetdentsCallback(cb *getdentsCallback) {
cb.t = nil
cb.buf = cb.buf[:0]
getdentsCallbackPool.Put(cb)
}
// Handle implements vfs.IterDirentsCallback.Handle.
func (cb *getdentsCallback) Handle(dirent vfs.Dirent) error {
remaining := len(cb.buf) - cb.copied
if cb.isGetdents64 {
// struct linux_dirent64 {
// ino64_t d_ino; /* 64-bit inode number */
// off64_t d_off; /* 64-bit offset to next structure */
// unsigned short d_reclen; /* Size of this dirent */
// unsigned char d_type; /* File type */
// char d_name[]; /* Filename (null-terminated) */
// };
size := DirentStructBytesWithoutName + len(dirent.Name)
size = (size + 7) &^ 7 // round up to multiple of 8
if size > remaining {
// This is only needed to imitate Linux, since it writes out to the user
// as it's iterating over dirs. We don't do that because we can't take
// the mm.mappingMu while holding the filesystem mutex.
if cb.copied == 0 && cb.userReportedSize >= size {
return linuxerr.EFAULT
}
return linuxerr.EINVAL
}
buf := cb.buf[cb.copied : cb.copied+size]
hostarch.ByteOrder.PutUint64(buf[0:8], dirent.Ino)
hostarch.ByteOrder.PutUint64(buf[8:16], uint64(dirent.NextOff))
hostarch.ByteOrder.PutUint16(buf[16:18], uint16(size))
buf[18] = dirent.Type
copy(buf[19:], dirent.Name)
// Zero out all remaining bytes in buf, including the NUL terminator
// after dirent.Name.
bufTail := buf[19+len(dirent.Name):]
clear(bufTail)
cb.copied += size
} else {
// struct linux_dirent {
// unsigned long d_ino; /* Inode number */
// unsigned long d_off; /* Offset to next linux_dirent */
// unsigned short d_reclen; /* Length of this linux_dirent */
// char d_name[]; /* Filename (null-terminated) */
// /* length is actually (d_reclen - 2 -
// offsetof(struct linux_dirent, d_name)) */
// /*
// char pad; // Zero padding byte
// char d_type; // File type (only since Linux
// // 2.6.4); offset is (d_reclen - 1)
// */
// };
if cb.t.Arch().Width() != 8 {
panic(fmt.Sprintf("unsupported sizeof(unsigned long): %d", cb.t.Arch().Width()))
}
size := DirentStructBytesWithoutName + len(dirent.Name)
size = (size + 7) &^ 7 // round up to multiple of sizeof(long)
if size > remaining {
if cb.copied == 0 && cb.userReportedSize >= size {
return linuxerr.EFAULT
}
return linuxerr.EINVAL
}
buf := cb.buf[cb.copied : cb.copied+size]
hostarch.ByteOrder.PutUint64(buf[0:8], dirent.Ino)
hostarch.ByteOrder.PutUint64(buf[8:16], uint64(dirent.NextOff))
hostarch.ByteOrder.PutUint16(buf[16:18], uint16(size))
copy(buf[18:], dirent.Name)
// Zero out all remaining bytes in buf, including the NUL terminator
// after dirent.Name and the zero padding byte between the name and
// dirent type.
bufTail := buf[18+len(dirent.Name) : size-1]
clear(bufTail)
buf[size-1] = dirent.Type
cb.copied += size
}
return nil
}
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