1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
|
package syscallcompat
import (
"bytes"
"syscall"
"golang.org/x/sys/unix"
"github.com/rfjakob/gocryptfs/internal/tlog"
)
// PATH_MAX is the maximum allowed path length on Linux.
// It is not defined on Darwin, so we use the Linux value.
const PATH_MAX = 4096
// Readlinkat is a convenience wrapper around unix.Readlinkat() that takes
// care of buffer sizing. Implemented like os.Readlink().
func Readlinkat(dirfd int, path string) (string, error) {
// Allocate the buffer exponentially like os.Readlink does.
for bufsz := 128; ; bufsz *= 2 {
buf := make([]byte, bufsz)
n, err := unix.Readlinkat(dirfd, path, buf)
if err != nil {
return "", err
}
if n < bufsz {
return string(buf[0:n]), nil
}
}
}
// Faccessat exists both in Linux and in MacOS 10.10+, but the Linux version
// DOES NOT support any flags. Emulate AT_SYMLINK_NOFOLLOW like glibc does.
func Faccessat(dirfd int, path string, mode uint32) error {
var st unix.Stat_t
err := Fstatat(dirfd, path, &st, unix.AT_SYMLINK_NOFOLLOW)
if err != nil {
return err
}
if st.Mode&syscall.S_IFMT == syscall.S_IFLNK {
// Pretend that a symlink is always accessible
return nil
}
return unix.Faccessat(dirfd, path, mode, 0)
}
// Openat wraps the Openat syscall.
func Openat(dirfd int, path string, flags int, mode uint32) (fd int, err error) {
if flags&syscall.O_CREAT != 0 {
// O_CREAT should be used with O_EXCL. O_NOFOLLOW has no effect with O_EXCL.
if flags&syscall.O_EXCL == 0 {
tlog.Warn.Printf("Openat: O_CREAT without O_EXCL: flags = %#x", flags)
flags |= syscall.O_EXCL
}
} else {
// If O_CREAT is not used, we should use O_NOFOLLOW
if flags&syscall.O_NOFOLLOW == 0 {
tlog.Warn.Printf("Openat: O_NOFOLLOW missing: flags = %#x", flags)
flags |= syscall.O_NOFOLLOW
}
}
return unix.Openat(dirfd, path, flags, mode)
}
// Linkat exists both in Linux and in MacOS 10.10+.
func Linkat(olddirfd int, oldpath string, newdirfd int, newpath string, flags int) (err error) {
return unix.Linkat(olddirfd, oldpath, newdirfd, newpath, flags)
}
const XATTR_SIZE_MAX = 65536
// Make the buffer 1kB bigger so we can detect overflows
const XATTR_BUFSZ = XATTR_SIZE_MAX + 1024
// Fgetxattr is a wrapper around unix.Fgetxattr that handles the buffer sizing.
func Fgetxattr(fd int, attr string) (val []byte, err error) {
// If the buffer is too small to fit the value, Linux and MacOS react
// differently:
// Linux: returns an ERANGE error and "-1" bytes.
// MacOS: truncates the value and returns "size" bytes.
//
// We choose the simple approach of buffer that is bigger than the limit on
// Linux, and return an error for everything that is bigger (which can
// only happen on MacOS).
//
// See https://github.com/pkg/xattr for a smarter solution.
// TODO: smarter buffer sizing?
buf := make([]byte, XATTR_BUFSZ)
sz, err := unix.Fgetxattr(fd, attr, buf)
if err == syscall.ERANGE {
// Do NOT return ERANGE - the user might retry ad inifinitum!
return nil, syscall.EOVERFLOW
}
if err != nil {
return nil, err
}
if sz >= XATTR_SIZE_MAX {
return nil, syscall.EOVERFLOW
}
// Copy only the actually used bytes to a new (smaller) buffer
// so "buf" never leaves the function and can be allocated on the stack.
val = make([]byte, sz)
copy(val, buf)
return val, nil
}
// Lgetxattr is a wrapper around unix.Lgetxattr that handles the buffer sizing.
func Lgetxattr(path string, attr string) (val []byte, err error) {
// See the buffer sizing comments in Fgetxattr.
// TODO: smarter buffer sizing?
buf := make([]byte, XATTR_BUFSZ)
sz, err := unix.Lgetxattr(path, attr, buf)
if err == syscall.ERANGE {
// Do NOT return ERANGE - the user might retry ad inifinitum!
return nil, syscall.EOVERFLOW
}
if err != nil {
return nil, err
}
if sz >= XATTR_SIZE_MAX {
return nil, syscall.EOVERFLOW
}
// Copy only the actually used bytes to a new (smaller) buffer
// so "buf" never leaves the function and can be allocated on the stack.
val = make([]byte, sz)
copy(val, buf)
return val, nil
}
// Flistxattr is a wrapper for unix.Flistxattr that handles buffer sizing and
// parsing the returned blob to a string slice.
func Flistxattr(fd int) (attrs []string, err error) {
// See the buffer sizing comments in Fgetxattr.
// TODO: smarter buffer sizing?
buf := make([]byte, XATTR_BUFSZ)
sz, err := unix.Flistxattr(fd, buf)
if err == syscall.ERANGE {
// Do NOT return ERANGE - the user might retry ad inifinitum!
return nil, syscall.EOVERFLOW
}
if err != nil {
return nil, err
}
if sz >= XATTR_SIZE_MAX {
return nil, syscall.EOVERFLOW
}
attrs = parseListxattrBlob(buf[:sz])
return attrs, nil
}
// Llistxattr is a wrapper for unix.Llistxattr that handles buffer sizing and
// parsing the returned blob to a string slice.
func Llistxattr(path string) (attrs []string, err error) {
// TODO: smarter buffer sizing?
buf := make([]byte, XATTR_BUFSZ)
sz, err := unix.Llistxattr(path, buf)
if err == syscall.ERANGE {
// Do NOT return ERANGE - the user might retry ad inifinitum!
return nil, syscall.EOVERFLOW
}
if err != nil {
return nil, err
}
if sz >= XATTR_SIZE_MAX {
return nil, syscall.EOVERFLOW
}
attrs = parseListxattrBlob(buf[:sz])
return attrs, nil
}
func parseListxattrBlob(buf []byte) (attrs []string) {
parts := bytes.Split(buf, []byte{0})
for _, part := range parts {
if len(part) == 0 {
// Last part is empty, ignore
continue
}
attrs = append(attrs, string(part))
}
return attrs
}
|
