xref: /linux/arch/um/drivers/cow_user.c (revision 8dd06ef34b6e2f41b29fbf5fc1663780f2524285)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Copyright (C) 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
4  */
5 
6 /*
7  * _XOPEN_SOURCE is needed for pread, but we define _GNU_SOURCE, which defines
8  * that.
9  */
10 #include <unistd.h>
11 #include <errno.h>
12 #include <string.h>
13 #include <arpa/inet.h>
14 #include <endian.h>
15 #include "cow.h"
16 #include "cow_sys.h"
17 
18 #define PATH_LEN_V1 256
19 
20 /* unsigned time_t works until year 2106 */
21 typedef __u32 time32_t;
22 
23 struct cow_header_v1 {
24 	__s32 magic;
25 	__s32 version;
26 	char backing_file[PATH_LEN_V1];
27 	time32_t mtime;
28 	__u64 size;
29 	__s32 sectorsize;
30 } __attribute__((packed));
31 
32 /*
33  * Define PATH_LEN_V3 as the usual value of MAXPATHLEN, just hard-code it in
34  * case other systems have different values for MAXPATHLEN.
35  *
36  * The same must hold for V2 - we want file format compatibility, not anything
37  * else.
38  */
39 #define PATH_LEN_V3 4096
40 #define PATH_LEN_V2 PATH_LEN_V3
41 
42 struct cow_header_v2 {
43 	__u32 magic;
44 	__u32 version;
45 	char backing_file[PATH_LEN_V2];
46 	time32_t mtime;
47 	__u64 size;
48 	__s32 sectorsize;
49 } __attribute__((packed));
50 
51 /*
52  * Changes from V2 -
53  *	PATH_LEN_V3 as described above
54  *	Explicitly specify field bit lengths for systems with different
55  *		lengths for the usual C types.  Not sure whether char or
56  *		time_t should be changed, this can be changed later without
57  *		breaking compatibility
58  *	Add alignment field so that different alignments can be used for the
59  *		bitmap and data
60  * 	Add cow_format field to allow for the possibility of different ways
61  *		of specifying the COW blocks.  For now, the only value is 0,
62  * 		for the traditional COW bitmap.
63  *	Move the backing_file field to the end of the header.  This allows
64  *		for the possibility of expanding it into the padding required
65  *		by the bitmap alignment.
66  * 	The bitmap and data portions of the file will be aligned as specified
67  * 		by the alignment field.  This is to allow COW files to be
68  *		put on devices with restrictions on access alignments, such as
69  *		/dev/raw, with a 512 byte alignment restriction.  This also
70  *		allows the data to be more aligned more strictly than on
71  *		sector boundaries.  This is needed for ubd-mmap, which needs
72  *		the data to be page aligned.
73  *	Fixed (finally!) the rounding bug
74  */
75 
76 /*
77  * Until Dec2005, __attribute__((packed)) was left out from the below
78  * definition, leading on 64-bit systems to 4 bytes of padding after mtime, to
79  * align size to 8-byte alignment.  This shifted all fields above (no padding
80  * was present on 32-bit, no other padding was added).
81  *
82  * However, this _can be detected_: it means that cow_format (always 0 until
83  * now) is shifted onto the first 4 bytes of backing_file, where it is otherwise
84  * impossible to find 4 zeros. -bb */
85 
86 struct cow_header_v3 {
87 	__u32 magic;
88 	__u32 version;
89 	__u32 mtime;
90 	__u64 size;
91 	__u32 sectorsize;
92 	__u32 alignment;
93 	__u32 cow_format;
94 	char backing_file[PATH_LEN_V3];
95 } __attribute__((packed));
96 
97 /* This is the broken layout used by some 64-bit binaries. */
98 struct cow_header_v3_broken {
99 	__u32 magic;
100 	__u32 version;
101 	__s64 mtime;
102 	__u64 size;
103 	__u32 sectorsize;
104 	__u32 alignment;
105 	__u32 cow_format;
106 	char backing_file[PATH_LEN_V3];
107 };
108 
109 /* COW format definitions - for now, we have only the usual COW bitmap */
110 #define COW_BITMAP 0
111 
112 union cow_header {
113 	struct cow_header_v1 v1;
114 	struct cow_header_v2 v2;
115 	struct cow_header_v3 v3;
116 	struct cow_header_v3_broken v3_b;
117 };
118 
119 #define COW_MAGIC 0x4f4f4f4d  /* MOOO */
120 #define COW_VERSION 3
121 
122 #define DIV_ROUND(x, len) (((x) + (len) - 1) / (len))
123 #define ROUND_UP(x, align) DIV_ROUND(x, align) * (align)
124 
cow_sizes(int version,__u64 size,int sectorsize,int align,int bitmap_offset,unsigned long * bitmap_len_out,int * data_offset_out)125 void cow_sizes(int version, __u64 size, int sectorsize, int align,
126 	       int bitmap_offset, unsigned long *bitmap_len_out,
127 	       int *data_offset_out)
128 {
129 	if (version < 3) {
130 		*bitmap_len_out = (size + sectorsize - 1) / (8 * sectorsize);
131 
132 		*data_offset_out = bitmap_offset + *bitmap_len_out;
133 		*data_offset_out = (*data_offset_out + sectorsize - 1) /
134 			sectorsize;
135 		*data_offset_out *= sectorsize;
136 	}
137 	else {
138 		*bitmap_len_out = DIV_ROUND(size, sectorsize);
139 		*bitmap_len_out = DIV_ROUND(*bitmap_len_out, 8);
140 
141 		*data_offset_out = bitmap_offset + *bitmap_len_out;
142 		*data_offset_out = ROUND_UP(*data_offset_out, align);
143 	}
144 }
145 
absolutize(char * to,int size,char * from)146 static int absolutize(char *to, int size, char *from)
147 {
148 	char save_cwd[256], *slash;
149 	int remaining;
150 
151 	if (getcwd(save_cwd, sizeof(save_cwd)) == NULL) {
152 		cow_printf("absolutize : unable to get cwd - errno = %d\n",
153 			   errno);
154 		return -1;
155 	}
156 	slash = strrchr(from, '/');
157 	if (slash != NULL) {
158 		*slash = '\0';
159 		if (chdir(from)) {
160 			*slash = '/';
161 			cow_printf("absolutize : Can't cd to '%s' - "
162 				   "errno = %d\n", from, errno);
163 			return -1;
164 		}
165 		*slash = '/';
166 		if (getcwd(to, size) == NULL) {
167 			cow_printf("absolutize : unable to get cwd of '%s' - "
168 			       "errno = %d\n", from, errno);
169 			return -1;
170 		}
171 		remaining = size - strlen(to);
172 		if (strlen(slash) + 1 > remaining) {
173 			cow_printf("absolutize : unable to fit '%s' into %d "
174 			       "chars\n", from, size);
175 			return -1;
176 		}
177 		strcat(to, slash);
178 	}
179 	else {
180 		if (strlen(save_cwd) + 1 + strlen(from) + 1 > size) {
181 			cow_printf("absolutize : unable to fit '%s' into %d "
182 			       "chars\n", from, size);
183 			return -1;
184 		}
185 		strcpy(to, save_cwd);
186 		strcat(to, "/");
187 		strcat(to, from);
188 	}
189 	if (chdir(save_cwd)) {
190 		cow_printf("absolutize : Can't cd to '%s' - "
191 			   "errno = %d\n", save_cwd, errno);
192 		return -1;
193 	}
194 	return 0;
195 }
196 
write_cow_header(char * cow_file,int fd,char * backing_file,int sectorsize,int alignment,unsigned long long * size)197 int write_cow_header(char *cow_file, int fd, char *backing_file,
198 		     int sectorsize, int alignment, unsigned long long *size)
199 {
200 	struct cow_header_v3 *header;
201 	long long modtime;
202 	int err;
203 
204 	err = cow_seek_file(fd, 0);
205 	if (err < 0) {
206 		cow_printf("write_cow_header - lseek failed, err = %d\n", -err);
207 		goto out;
208 	}
209 
210 	err = -ENOMEM;
211 	header = cow_malloc(sizeof(*header));
212 	if (header == NULL) {
213 		cow_printf("write_cow_header - failed to allocate COW V3 "
214 			   "header\n");
215 		goto out;
216 	}
217 	header->magic = htobe32(COW_MAGIC);
218 	header->version = htobe32(COW_VERSION);
219 
220 	err = -EINVAL;
221 	if (strlen(backing_file) > sizeof(header->backing_file) - 1) {
222 		/* Below, %zd is for a size_t value */
223 		cow_printf("Backing file name \"%s\" is too long - names are "
224 			   "limited to %zd characters\n", backing_file,
225 			   sizeof(header->backing_file) - 1);
226 		goto out_free;
227 	}
228 
229 	if (absolutize(header->backing_file, sizeof(header->backing_file),
230 		      backing_file))
231 		goto out_free;
232 
233 	err = os_file_modtime(header->backing_file, &modtime);
234 	if (err < 0) {
235 		cow_printf("write_cow_header - backing file '%s' mtime "
236 			   "request failed, err = %d\n", header->backing_file,
237 			   -err);
238 		goto out_free;
239 	}
240 
241 	err = cow_file_size(header->backing_file, size);
242 	if (err < 0) {
243 		cow_printf("write_cow_header - couldn't get size of "
244 			   "backing file '%s', err = %d\n",
245 			   header->backing_file, -err);
246 		goto out_free;
247 	}
248 
249 	header->mtime = htobe32(modtime);
250 	header->size = htobe64(*size);
251 	header->sectorsize = htobe32(sectorsize);
252 	header->alignment = htobe32(alignment);
253 	header->cow_format = COW_BITMAP;
254 
255 	err = cow_write_file(fd, header, sizeof(*header));
256 	if (err != sizeof(*header)) {
257 		cow_printf("write_cow_header - write of header to "
258 			   "new COW file '%s' failed, err = %d\n", cow_file,
259 			   -err);
260 		goto out_free;
261 	}
262 	err = 0;
263  out_free:
264 	cow_free(header);
265  out:
266 	return err;
267 }
268 
file_reader(__u64 offset,char * buf,int len,void * arg)269 int file_reader(__u64 offset, char *buf, int len, void *arg)
270 {
271 	int fd = *((int *) arg);
272 
273 	return pread(fd, buf, len, offset);
274 }
275 
276 /* XXX Need to sanity-check the values read from the header */
277 
read_cow_header(int (* reader)(__u64,char *,int,void *),void * arg,__u32 * version_out,char ** backing_file_out,long long * mtime_out,unsigned long long * size_out,int * sectorsize_out,__u32 * align_out,int * bitmap_offset_out)278 int read_cow_header(int (*reader)(__u64, char *, int, void *), void *arg,
279 		    __u32 *version_out, char **backing_file_out,
280 		    long long *mtime_out, unsigned long long *size_out,
281 		    int *sectorsize_out, __u32 *align_out,
282 		    int *bitmap_offset_out)
283 {
284 	union cow_header *header;
285 	char *file;
286 	int err, n;
287 	unsigned long version, magic;
288 
289 	header = cow_malloc(sizeof(*header));
290 	if (header == NULL) {
291 	        cow_printf("read_cow_header - Failed to allocate header\n");
292 		return -ENOMEM;
293 	}
294 	err = -EINVAL;
295 	n = (*reader)(0, (char *) header, sizeof(*header), arg);
296 	if (n < offsetof(typeof(header->v1), backing_file)) {
297 		cow_printf("read_cow_header - short header\n");
298 		goto out;
299 	}
300 
301 	magic = header->v1.magic;
302 	if (magic == COW_MAGIC)
303 		version = header->v1.version;
304 	else if (magic == be32toh(COW_MAGIC))
305 		version = be32toh(header->v1.version);
306 	/* No error printed because the non-COW case comes through here */
307 	else goto out;
308 
309 	*version_out = version;
310 
311 	if (version == 1) {
312 		if (n < sizeof(header->v1)) {
313 			cow_printf("read_cow_header - failed to read V1 "
314 				   "header\n");
315 			goto out;
316 		}
317 		*mtime_out = header->v1.mtime;
318 		*size_out = header->v1.size;
319 		*sectorsize_out = header->v1.sectorsize;
320 		*bitmap_offset_out = sizeof(header->v1);
321 		*align_out = *sectorsize_out;
322 		file = header->v1.backing_file;
323 	}
324 	else if (version == 2) {
325 		if (n < sizeof(header->v2)) {
326 			cow_printf("read_cow_header - failed to read V2 "
327 				   "header\n");
328 			goto out;
329 		}
330 		*mtime_out = be32toh(header->v2.mtime);
331 		*size_out = be64toh(header->v2.size);
332 		*sectorsize_out = be32toh(header->v2.sectorsize);
333 		*bitmap_offset_out = sizeof(header->v2);
334 		*align_out = *sectorsize_out;
335 		file = header->v2.backing_file;
336 	}
337 	/* This is very subtle - see above at union cow_header definition */
338 	else if (version == 3 && (*((int*)header->v3.backing_file) != 0)) {
339 		if (n < sizeof(header->v3)) {
340 			cow_printf("read_cow_header - failed to read V3 "
341 				   "header\n");
342 			goto out;
343 		}
344 		*mtime_out = be32toh(header->v3.mtime);
345 		*size_out = be64toh(header->v3.size);
346 		*sectorsize_out = be32toh(header->v3.sectorsize);
347 		*align_out = be32toh(header->v3.alignment);
348 		if (*align_out == 0) {
349 			cow_printf("read_cow_header - invalid COW header, "
350 				   "align == 0\n");
351 		}
352 		*bitmap_offset_out = ROUND_UP(sizeof(header->v3), *align_out);
353 		file = header->v3.backing_file;
354 	}
355 	else if (version == 3) {
356 		cow_printf("read_cow_header - broken V3 file with"
357 			   " 64-bit layout - recovering content.\n");
358 
359 		if (n < sizeof(header->v3_b)) {
360 			cow_printf("read_cow_header - failed to read V3 "
361 				   "header\n");
362 			goto out;
363 		}
364 
365 		/*
366 		 * this was used until Dec2005 - 64bits are needed to represent
367 		 * 2106+. I.e. we can safely do this truncating cast.
368 		 *
369 		 * Additionally, we must use be32toh() instead of be64toh(), since
370 		 * the program used to use the former (tested - I got mtime
371 		 * mismatch "0 vs whatever").
372 		 *
373 		 * Ever heard about bug-to-bug-compatibility ? ;-) */
374 		*mtime_out = (time32_t) be32toh(header->v3_b.mtime);
375 
376 		*size_out = be64toh(header->v3_b.size);
377 		*sectorsize_out = be32toh(header->v3_b.sectorsize);
378 		*align_out = be32toh(header->v3_b.alignment);
379 		if (*align_out == 0) {
380 			cow_printf("read_cow_header - invalid COW header, "
381 				   "align == 0\n");
382 		}
383 		*bitmap_offset_out = ROUND_UP(sizeof(header->v3_b), *align_out);
384 		file = header->v3_b.backing_file;
385 	}
386 	else {
387 		cow_printf("read_cow_header - invalid COW version\n");
388 		goto out;
389 	}
390 	err = -ENOMEM;
391 	*backing_file_out = cow_strdup(file);
392 	if (*backing_file_out == NULL) {
393 		cow_printf("read_cow_header - failed to allocate backing "
394 			   "file\n");
395 		goto out;
396 	}
397 	err = 0;
398  out:
399 	cow_free(header);
400 	return err;
401 }
402 
init_cow_file(int fd,char * cow_file,char * backing_file,int sectorsize,int alignment,int * bitmap_offset_out,unsigned long * bitmap_len_out,int * data_offset_out)403 int init_cow_file(int fd, char *cow_file, char *backing_file, int sectorsize,
404 		  int alignment, int *bitmap_offset_out,
405 		  unsigned long *bitmap_len_out, int *data_offset_out)
406 {
407 	unsigned long long size, offset;
408 	char zero = 0;
409 	int err;
410 
411 	err = write_cow_header(cow_file, fd, backing_file, sectorsize,
412 			       alignment, &size);
413 	if (err)
414 		goto out;
415 
416 	*bitmap_offset_out = ROUND_UP(sizeof(struct cow_header_v3), alignment);
417 	cow_sizes(COW_VERSION, size, sectorsize, alignment, *bitmap_offset_out,
418 		  bitmap_len_out, data_offset_out);
419 
420 	offset = *data_offset_out + size - sizeof(zero);
421 	err = cow_seek_file(fd, offset);
422 	if (err < 0) {
423 		cow_printf("cow bitmap lseek failed : err = %d\n", -err);
424 		goto out;
425 	}
426 
427 	/*
428 	 * does not really matter how much we write it is just to set EOF
429 	 * this also sets the entire COW bitmap
430 	 * to zero without having to allocate it
431 	 */
432 	err = cow_write_file(fd, &zero, sizeof(zero));
433 	if (err != sizeof(zero)) {
434 		cow_printf("Write of bitmap to new COW file '%s' failed, "
435 			   "err = %d\n", cow_file, -err);
436 		if (err >= 0)
437 			err = -EINVAL;
438 		goto out;
439 	}
440 
441 	return 0;
442  out:
443 	return err;
444 }
445