1 | /* Copyright (C) 1993-2018 Free Software Foundation, Inc. |
2 | This file is part of the GNU C Library. |
3 | |
4 | The GNU C Library is free software; you can redistribute it and/or |
5 | modify it under the terms of the GNU Lesser General Public |
6 | License as published by the Free Software Foundation; either |
7 | version 2.1 of the License, or (at your option) any later version. |
8 | |
9 | The GNU C Library is distributed in the hope that it will be useful, |
10 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
12 | Lesser General Public License for more details. |
13 | |
14 | You should have received a copy of the GNU Lesser General Public |
15 | License along with the GNU C Library; if not, see |
16 | <http://www.gnu.org/licenses/>. */ |
17 | |
18 | #include <alloca.h> |
19 | #include <assert.h> |
20 | #include <errno.h> |
21 | #include <dirent.h> |
22 | #include <stddef.h> |
23 | #include <stdint.h> |
24 | #include <string.h> |
25 | #include <unistd.h> |
26 | #include <sys/param.h> |
27 | #include <sys/types.h> |
28 | |
29 | #include <sysdep.h> |
30 | #include <sys/syscall.h> |
31 | |
32 | #include <linux/posix_types.h> |
33 | |
34 | #include <kernel-features.h> |
35 | |
36 | /* For Linux we need a special version of this file since the |
37 | definition of `struct dirent' is not the same for the kernel and |
38 | the libc. There is one additional field which might be introduced |
39 | in the kernel structure in the future. |
40 | |
41 | Here is the kernel definition of `struct dirent' as of 2.1.20: */ |
42 | |
43 | struct kernel_dirent |
44 | { |
45 | long int d_ino; |
46 | __kernel_off_t d_off; |
47 | unsigned short int d_reclen; |
48 | char d_name[256]; |
49 | }; |
50 | |
51 | struct kernel_dirent64 |
52 | { |
53 | uint64_t d_ino; |
54 | int64_t d_off; |
55 | unsigned short int d_reclen; |
56 | unsigned char d_type; |
57 | char d_name[256]; |
58 | }; |
59 | |
60 | #ifndef __GETDENTS |
61 | # define __GETDENTS __getdents |
62 | #endif |
63 | #ifndef DIRENT_TYPE |
64 | # define DIRENT_TYPE struct dirent |
65 | #endif |
66 | #ifndef DIRENT_SET_DP_INO |
67 | # define DIRENT_SET_DP_INO(dp, value) (dp)->d_ino = (value) |
68 | #endif |
69 | |
70 | /* The problem here is that we cannot simply read the next NBYTES |
71 | bytes. We need to take the additional field into account. We use |
72 | some heuristic. Assuming the directory contains names with 14 |
73 | characters on average we can compute an estimated number of entries |
74 | which fit in the buffer. Taking this number allows us to specify a |
75 | reasonable number of bytes to read. If we should be wrong, we can |
76 | reset the file descriptor. In practice the kernel is limiting the |
77 | amount of data returned much more then the reduced buffer size. */ |
78 | ssize_t |
79 | __GETDENTS (int fd, char *buf, size_t nbytes) |
80 | { |
81 | ssize_t retval; |
82 | |
83 | /* The d_ino and d_off fields in kernel_dirent and dirent must have |
84 | the same sizes and alignments. */ |
85 | if (sizeof (DIRENT_TYPE) == sizeof (struct dirent) |
86 | && (sizeof (((struct kernel_dirent *) 0)->d_ino) |
87 | == sizeof (((struct dirent *) 0)->d_ino)) |
88 | && (sizeof (((struct kernel_dirent *) 0)->d_off) |
89 | == sizeof (((struct dirent *) 0)->d_off)) |
90 | && (offsetof (struct kernel_dirent, d_off) |
91 | == offsetof (struct dirent, d_off)) |
92 | && (offsetof (struct kernel_dirent, d_reclen) |
93 | == offsetof (struct dirent, d_reclen))) |
94 | { |
95 | retval = INLINE_SYSCALL (getdents, 3, fd, buf, nbytes); |
96 | |
97 | /* The kernel added the d_type value after the name. Change |
98 | this now. */ |
99 | if (retval != -1) |
100 | { |
101 | union |
102 | { |
103 | struct kernel_dirent k; |
104 | struct dirent u; |
105 | } *kbuf = (void *) buf; |
106 | |
107 | while ((char *) kbuf < buf + retval) |
108 | { |
109 | char d_type = *((char *) kbuf + kbuf->k.d_reclen - 1); |
110 | memmove (kbuf->u.d_name, kbuf->k.d_name, |
111 | strlen (kbuf->k.d_name) + 1); |
112 | kbuf->u.d_type = d_type; |
113 | |
114 | kbuf = (void *) ((char *) kbuf + kbuf->k.d_reclen); |
115 | } |
116 | } |
117 | |
118 | return retval; |
119 | } |
120 | |
121 | off64_t last_offset = -1; |
122 | |
123 | #ifdef __NR_getdents64 |
124 | { |
125 | union |
126 | { |
127 | struct kernel_dirent64 k; |
128 | DIRENT_TYPE u; |
129 | char b[1]; |
130 | } *kbuf = (void *) buf, *outp, *inp; |
131 | size_t kbytes = nbytes; |
132 | if (offsetof (DIRENT_TYPE, d_name) |
133 | < offsetof (struct kernel_dirent64, d_name) |
134 | && nbytes <= sizeof (DIRENT_TYPE)) |
135 | { |
136 | kbytes = (nbytes + offsetof (struct kernel_dirent64, d_name) |
137 | - offsetof (DIRENT_TYPE, d_name)); |
138 | kbuf = __alloca(kbytes); |
139 | } |
140 | retval = INLINE_SYSCALL (getdents64, 3, fd, kbuf, kbytes); |
141 | const size_t size_diff = (offsetof (struct kernel_dirent64, d_name) |
142 | - offsetof (DIRENT_TYPE, d_name)); |
143 | |
144 | /* Return the error if encountered. */ |
145 | if (retval == -1) |
146 | return -1; |
147 | |
148 | /* If the structure returned by the kernel is identical to what we |
149 | need, don't do any conversions. */ |
150 | if (offsetof (DIRENT_TYPE, d_name) |
151 | == offsetof (struct kernel_dirent64, d_name) |
152 | && sizeof (outp->u.d_ino) == sizeof (inp->k.d_ino) |
153 | && sizeof (outp->u.d_off) == sizeof (inp->k.d_off)) |
154 | return retval; |
155 | |
156 | /* These two pointers might alias the same memory buffer. |
157 | Standard C requires that we always use the same type for them, |
158 | so we must use the union type. */ |
159 | inp = kbuf; |
160 | outp = (void *) buf; |
161 | |
162 | while (&inp->b < &kbuf->b + retval) |
163 | { |
164 | const size_t alignment = __alignof__ (DIRENT_TYPE); |
165 | /* Since inp->k.d_reclen is already aligned for the kernel |
166 | structure this may compute a value that is bigger |
167 | than necessary. */ |
168 | size_t old_reclen = inp->k.d_reclen; |
169 | size_t new_reclen = ((old_reclen - size_diff + alignment - 1) |
170 | & ~(alignment - 1)); |
171 | |
172 | /* Copy the data out of the old structure into temporary space. |
173 | Then copy the name, which may overlap if BUF == KBUF. */ |
174 | const uint64_t d_ino = inp->k.d_ino; |
175 | const int64_t d_off = inp->k.d_off; |
176 | const uint8_t d_type = inp->k.d_type; |
177 | |
178 | memmove (outp->u.d_name, inp->k.d_name, |
179 | old_reclen - offsetof (struct kernel_dirent64, d_name)); |
180 | |
181 | /* Now we have copied the data from INP and access only OUTP. */ |
182 | |
183 | DIRENT_SET_DP_INO (&outp->u, d_ino); |
184 | outp->u.d_off = d_off; |
185 | if ((sizeof (outp->u.d_ino) != sizeof (inp->k.d_ino) |
186 | && outp->u.d_ino != d_ino) |
187 | || (sizeof (outp->u.d_off) != sizeof (inp->k.d_off) |
188 | && outp->u.d_off != d_off)) |
189 | { |
190 | /* Overflow. If there was at least one entry |
191 | before this one, return them without error, |
192 | otherwise signal overflow. */ |
193 | if (last_offset != -1) |
194 | { |
195 | __lseek64 (fd, last_offset, SEEK_SET); |
196 | return outp->b - buf; |
197 | } |
198 | __set_errno (EOVERFLOW); |
199 | return -1; |
200 | } |
201 | |
202 | last_offset = d_off; |
203 | outp->u.d_reclen = new_reclen; |
204 | outp->u.d_type = d_type; |
205 | |
206 | inp = (void *) inp + old_reclen; |
207 | outp = (void *) outp + new_reclen; |
208 | } |
209 | |
210 | return outp->b - buf; |
211 | } |
212 | #endif |
213 | { |
214 | size_t red_nbytes; |
215 | struct kernel_dirent *skdp, *kdp; |
216 | const size_t size_diff = (offsetof (DIRENT_TYPE, d_name) |
217 | - offsetof (struct kernel_dirent, d_name)); |
218 | |
219 | red_nbytes = MIN (nbytes |
220 | - ((nbytes / (offsetof (DIRENT_TYPE, d_name) + 14)) |
221 | * size_diff), |
222 | nbytes - size_diff); |
223 | |
224 | skdp = kdp = __alloca (red_nbytes); |
225 | |
226 | retval = INLINE_SYSCALL (getdents, 3, fd, (char *) kdp, red_nbytes); |
227 | |
228 | if (retval == -1) |
229 | return -1; |
230 | |
231 | DIRENT_TYPE *dp = (DIRENT_TYPE *) buf; |
232 | while ((char *) kdp < (char *) skdp + retval) |
233 | { |
234 | const size_t alignment = __alignof__ (DIRENT_TYPE); |
235 | /* Since kdp->d_reclen is already aligned for the kernel structure |
236 | this may compute a value that is bigger than necessary. */ |
237 | size_t new_reclen = ((kdp->d_reclen + size_diff + alignment - 1) |
238 | & ~(alignment - 1)); |
239 | if ((char *) dp + new_reclen > buf + nbytes) |
240 | { |
241 | /* Our heuristic failed. We read too many entries. Reset |
242 | the stream. */ |
243 | assert (last_offset != -1); |
244 | __lseek64 (fd, last_offset, SEEK_SET); |
245 | |
246 | if ((char *) dp == buf) |
247 | { |
248 | /* The buffer the user passed in is too small to hold even |
249 | one entry. */ |
250 | __set_errno (EINVAL); |
251 | return -1; |
252 | } |
253 | |
254 | break; |
255 | } |
256 | |
257 | last_offset = kdp->d_off; |
258 | DIRENT_SET_DP_INO(dp, kdp->d_ino); |
259 | dp->d_off = kdp->d_off; |
260 | dp->d_reclen = new_reclen; |
261 | dp->d_type = *((char *) kdp + kdp->d_reclen - 1); |
262 | memcpy (dp->d_name, kdp->d_name, |
263 | kdp->d_reclen - offsetof (struct kernel_dirent, d_name)); |
264 | |
265 | dp = (DIRENT_TYPE *) ((char *) dp + new_reclen); |
266 | kdp = (struct kernel_dirent *) (((char *) kdp) + kdp->d_reclen); |
267 | } |
268 | |
269 | return (char *) dp - buf; |
270 | } |
271 | } |
272 | |