1 /* Get directory entries. Linux LFS version.
2 Copyright (C) 1997-2023 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library. If not, see
17 <https://www.gnu.org/licenses/>. */
18
19 #include <string.h>
20 #include <dirent.h>
21 #include <errno.h>
22 #include <limits.h>
23
24 /* The kernel struct linux_dirent64 matches the 'struct dirent64' type. */
25 ssize_t
26 __getdents64 (int fd, void *buf, size_t nbytes)
27 {
28 /* The system call takes an unsigned int argument, and some length
29 checks in the kernel use an int type. */
30 if (nbytes > INT_MAX)
31 nbytes = INT_MAX;
32 return INLINE_SYSCALL_CALL (getdents64, fd, buf, nbytes);
33 }
34 libc_hidden_def (__getdents64)
35 weak_alias (__getdents64, getdents64)
36
37 #if _DIRENT_MATCHES_DIRENT64
38 strong_alias (__getdents64, __getdents)
39 #else
40 # include <shlib-compat.h>
41
42 # if SHLIB_COMPAT(libc, GLIBC_2_1, GLIBC_2_2)
43 # include <olddirent.h>
44 # include <unistd.h>
45
46 static ssize_t
47 handle_overflow (int fd, __off64_t offset, ssize_t count)
48 {
49 /* If this is the first entry in the buffer, we can report the
50 error. */
51 if (offset == 0)
52 {
53 __set_errno (EOVERFLOW);
54 return -1;
55 }
56
57 /* Otherwise, seek to the overflowing entry, so that the next call
58 will report the error, and return the data read so far. */
59 if (__lseek64 (fd, offset, SEEK_SET) != 0)
60 return -1;
61 return count;
62 }
63
64 ssize_t
65 __old_getdents64 (int fd, char *buf, size_t nbytes)
66 {
67 /* We do not move the individual directory entries. This is only
68 possible if the target type (struct __old_dirent64) is smaller
69 than the source type. */
70 _Static_assert (offsetof (struct __old_dirent64, d_name)
71 <= offsetof (struct dirent64, d_name),
72 "__old_dirent64 is larger than dirent64");
73 _Static_assert (__alignof__ (struct __old_dirent64)
74 <= __alignof__ (struct dirent64),
75 "alignment of __old_dirent64 is larger than dirent64");
76
77 ssize_t retval = INLINE_SYSCALL_CALL (getdents64, fd, buf, nbytes);
78 if (retval > 0)
79 {
80 /* This is the marker for the first entry. Offset 0 is reserved
81 for the first entry (see rewinddir). Here, we use it as a
82 marker for the first entry in the buffer. We never actually
83 seek to offset 0 because handle_overflow reports the error
84 directly, so it does not matter that the offset is incorrect
85 if entries have been read from the descriptor before (so that
86 the descriptor is not actually at offset 0). */
87 __off64_t previous_offset = 0;
88
89 char *p = buf;
90 char *end = buf + retval;
91 while (p < end)
92 {
93 struct dirent64 *source = (struct dirent64 *) p;
94
95 /* Copy out the fixed-size data. */
96 __ino_t ino = source->d_ino;
97 __off64_t offset = source->d_off;
98 unsigned int reclen = source->d_reclen;
99 unsigned char type = source->d_type;
100
101 /* Check for ino_t overflow. */
102 if (__glibc_unlikely (ino != source->d_ino))
103 return handle_overflow (fd, previous_offset, p - buf);
104
105 /* Convert to the target layout. Use a separate struct and
106 memcpy to side-step aliasing issues. */
107 struct __old_dirent64 result;
108 result.d_ino = ino;
109 result.d_off = offset;
110 result.d_reclen = reclen;
111 result.d_type = type;
112
113 /* Write the fixed-sized part of the result to the
114 buffer. */
115 size_t result_name_offset = offsetof (struct __old_dirent64, d_name);
116 memcpy (p, &result, result_name_offset);
117
118 /* Adjust the position of the name if necessary. Copy
119 everything until the end of the record, including the
120 terminating NUL byte. */
121 if (result_name_offset != offsetof (struct dirent64, d_name))
122 memmove (p + result_name_offset, source->d_name,
123 reclen - offsetof (struct dirent64, d_name));
124
125 p += reclen;
126 previous_offset = offset;
127 }
128 }
129 return retval;
130 }
131 # endif /* SHLIB_COMPAT(libc, GLIBC_2_1, GLIBC_2_2) */
132 #endif /* _DIRENT_MATCHES_DIRENT64 */