1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/fs.h>
3 #include <linux/random.h>
4 #include <linux/buffer_head.h>
5 #include <linux/utsname.h>
6 #include <linux/kthread.h>
7
8 #include "ext4.h"
9
10 /* Checksumming functions */
ext4_mmp_csum(struct super_block * sb,struct mmp_struct * mmp)11 static __le32 ext4_mmp_csum(struct super_block *sb, struct mmp_struct *mmp)
12 {
13 struct ext4_sb_info *sbi = EXT4_SB(sb);
14 int offset = offsetof(struct mmp_struct, mmp_checksum);
15 __u32 csum;
16
17 csum = ext4_chksum(sbi, sbi->s_csum_seed, (char *)mmp, offset);
18
19 return cpu_to_le32(csum);
20 }
21
ext4_mmp_csum_verify(struct super_block * sb,struct mmp_struct * mmp)22 static int ext4_mmp_csum_verify(struct super_block *sb, struct mmp_struct *mmp)
23 {
24 if (!ext4_has_metadata_csum(sb))
25 return 1;
26
27 return mmp->mmp_checksum == ext4_mmp_csum(sb, mmp);
28 }
29
ext4_mmp_csum_set(struct super_block * sb,struct mmp_struct * mmp)30 static void ext4_mmp_csum_set(struct super_block *sb, struct mmp_struct *mmp)
31 {
32 if (!ext4_has_metadata_csum(sb))
33 return;
34
35 mmp->mmp_checksum = ext4_mmp_csum(sb, mmp);
36 }
37
38 /*
39 * Write the MMP block using REQ_SYNC to try to get the block on-disk
40 * faster.
41 */
write_mmp_block(struct super_block * sb,struct buffer_head * bh)42 static int write_mmp_block(struct super_block *sb, struct buffer_head *bh)
43 {
44 struct mmp_struct *mmp = (struct mmp_struct *)(bh->b_data);
45
46 /*
47 * We protect against freezing so that we don't create dirty buffers
48 * on frozen filesystem.
49 */
50 sb_start_write(sb);
51 ext4_mmp_csum_set(sb, mmp);
52 lock_buffer(bh);
53 bh->b_end_io = end_buffer_write_sync;
54 get_bh(bh);
55 submit_bh(REQ_OP_WRITE, REQ_SYNC | REQ_META | REQ_PRIO, bh);
56 wait_on_buffer(bh);
57 sb_end_write(sb);
58 if (unlikely(!buffer_uptodate(bh)))
59 return 1;
60
61 return 0;
62 }
63
64 /*
65 * Read the MMP block. It _must_ be read from disk and hence we clear the
66 * uptodate flag on the buffer.
67 */
read_mmp_block(struct super_block * sb,struct buffer_head ** bh,ext4_fsblk_t mmp_block)68 static int read_mmp_block(struct super_block *sb, struct buffer_head **bh,
69 ext4_fsblk_t mmp_block)
70 {
71 struct mmp_struct *mmp;
72 int ret;
73
74 if (*bh)
75 clear_buffer_uptodate(*bh);
76
77 /* This would be sb_bread(sb, mmp_block), except we need to be sure
78 * that the MD RAID device cache has been bypassed, and that the read
79 * is not blocked in the elevator. */
80 if (!*bh) {
81 *bh = sb_getblk(sb, mmp_block);
82 if (!*bh) {
83 ret = -ENOMEM;
84 goto warn_exit;
85 }
86 }
87
88 get_bh(*bh);
89 lock_buffer(*bh);
90 (*bh)->b_end_io = end_buffer_read_sync;
91 submit_bh(REQ_OP_READ, REQ_META | REQ_PRIO, *bh);
92 wait_on_buffer(*bh);
93 if (!buffer_uptodate(*bh)) {
94 ret = -EIO;
95 goto warn_exit;
96 }
97 mmp = (struct mmp_struct *)((*bh)->b_data);
98 if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC) {
99 ret = -EFSCORRUPTED;
100 goto warn_exit;
101 }
102 if (!ext4_mmp_csum_verify(sb, mmp)) {
103 ret = -EFSBADCRC;
104 goto warn_exit;
105 }
106 return 0;
107 warn_exit:
108 brelse(*bh);
109 *bh = NULL;
110 ext4_warning(sb, "Error %d while reading MMP block %llu",
111 ret, mmp_block);
112 return ret;
113 }
114
115 /*
116 * Dump as much information as possible to help the admin.
117 */
__dump_mmp_msg(struct super_block * sb,struct mmp_struct * mmp,const char * function,unsigned int line,const char * msg)118 void __dump_mmp_msg(struct super_block *sb, struct mmp_struct *mmp,
119 const char *function, unsigned int line, const char *msg)
120 {
121 __ext4_warning(sb, function, line, "%s", msg);
122 __ext4_warning(sb, function, line,
123 "MMP failure info: last update time: %llu, last update node: %.*s, last update device: %.*s",
124 (unsigned long long)le64_to_cpu(mmp->mmp_time),
125 (int)sizeof(mmp->mmp_nodename), mmp->mmp_nodename,
126 (int)sizeof(mmp->mmp_bdevname), mmp->mmp_bdevname);
127 }
128
129 /*
130 * kmmpd will update the MMP sequence every s_mmp_update_interval seconds
131 */
kmmpd(void * data)132 static int kmmpd(void *data)
133 {
134 struct super_block *sb = ((struct mmpd_data *) data)->sb;
135 struct buffer_head *bh = ((struct mmpd_data *) data)->bh;
136 struct ext4_super_block *es = EXT4_SB(sb)->s_es;
137 struct mmp_struct *mmp;
138 ext4_fsblk_t mmp_block;
139 u32 seq = 0;
140 unsigned long failed_writes = 0;
141 int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval);
142 unsigned mmp_check_interval;
143 unsigned long last_update_time;
144 unsigned long diff;
145 int retval;
146
147 mmp_block = le64_to_cpu(es->s_mmp_block);
148 mmp = (struct mmp_struct *)(bh->b_data);
149 mmp->mmp_time = cpu_to_le64(ktime_get_real_seconds());
150 /*
151 * Start with the higher mmp_check_interval and reduce it if
152 * the MMP block is being updated on time.
153 */
154 mmp_check_interval = max(EXT4_MMP_CHECK_MULT * mmp_update_interval,
155 EXT4_MMP_MIN_CHECK_INTERVAL);
156 mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
157 BUILD_BUG_ON(sizeof(mmp->mmp_bdevname) < BDEVNAME_SIZE);
158 bdevname(bh->b_bdev, mmp->mmp_bdevname);
159
160 memcpy(mmp->mmp_nodename, init_utsname()->nodename,
161 sizeof(mmp->mmp_nodename));
162
163 while (!kthread_should_stop()) {
164 if (++seq > EXT4_MMP_SEQ_MAX)
165 seq = 1;
166
167 mmp->mmp_seq = cpu_to_le32(seq);
168 mmp->mmp_time = cpu_to_le64(ktime_get_real_seconds());
169 last_update_time = jiffies;
170
171 retval = write_mmp_block(sb, bh);
172 /*
173 * Don't spew too many error messages. Print one every
174 * (s_mmp_update_interval * 60) seconds.
175 */
176 if (retval) {
177 if ((failed_writes % 60) == 0)
178 ext4_error(sb, "Error writing to MMP block");
179 failed_writes++;
180 }
181
182 if (!(le32_to_cpu(es->s_feature_incompat) &
183 EXT4_FEATURE_INCOMPAT_MMP)) {
184 ext4_warning(sb, "kmmpd being stopped since MMP feature"
185 " has been disabled.");
186 goto exit_thread;
187 }
188
189 if (sb_rdonly(sb))
190 break;
191
192 diff = jiffies - last_update_time;
193 if (diff < mmp_update_interval * HZ)
194 schedule_timeout_interruptible(mmp_update_interval *
195 HZ - diff);
196
197 /*
198 * We need to make sure that more than mmp_check_interval
199 * seconds have not passed since writing. If that has happened
200 * we need to check if the MMP block is as we left it.
201 */
202 diff = jiffies - last_update_time;
203 if (diff > mmp_check_interval * HZ) {
204 struct buffer_head *bh_check = NULL;
205 struct mmp_struct *mmp_check;
206
207 retval = read_mmp_block(sb, &bh_check, mmp_block);
208 if (retval) {
209 ext4_error(sb, "error reading MMP data: %d",
210 retval);
211 goto exit_thread;
212 }
213
214 mmp_check = (struct mmp_struct *)(bh_check->b_data);
215 if (mmp->mmp_seq != mmp_check->mmp_seq ||
216 memcmp(mmp->mmp_nodename, mmp_check->mmp_nodename,
217 sizeof(mmp->mmp_nodename))) {
218 dump_mmp_msg(sb, mmp_check,
219 "Error while updating MMP info. "
220 "The filesystem seems to have been"
221 " multiply mounted.");
222 ext4_error(sb, "abort");
223 put_bh(bh_check);
224 retval = -EBUSY;
225 goto exit_thread;
226 }
227 put_bh(bh_check);
228 }
229
230 /*
231 * Adjust the mmp_check_interval depending on how much time
232 * it took for the MMP block to be written.
233 */
234 mmp_check_interval = max(min(EXT4_MMP_CHECK_MULT * diff / HZ,
235 EXT4_MMP_MAX_CHECK_INTERVAL),
236 EXT4_MMP_MIN_CHECK_INTERVAL);
237 mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
238 }
239
240 /*
241 * Unmount seems to be clean.
242 */
243 mmp->mmp_seq = cpu_to_le32(EXT4_MMP_SEQ_CLEAN);
244 mmp->mmp_time = cpu_to_le64(ktime_get_real_seconds());
245
246 retval = write_mmp_block(sb, bh);
247
248 exit_thread:
249 EXT4_SB(sb)->s_mmp_tsk = NULL;
250 kfree(data);
251 brelse(bh);
252 return retval;
253 }
254
255 /*
256 * Get a random new sequence number but make sure it is not greater than
257 * EXT4_MMP_SEQ_MAX.
258 */
mmp_new_seq(void)259 static unsigned int mmp_new_seq(void)
260 {
261 u32 new_seq;
262
263 do {
264 new_seq = prandom_u32();
265 } while (new_seq > EXT4_MMP_SEQ_MAX);
266
267 return new_seq;
268 }
269
270 /*
271 * Protect the filesystem from being mounted more than once.
272 */
ext4_multi_mount_protect(struct super_block * sb,ext4_fsblk_t mmp_block)273 int ext4_multi_mount_protect(struct super_block *sb,
274 ext4_fsblk_t mmp_block)
275 {
276 struct ext4_super_block *es = EXT4_SB(sb)->s_es;
277 struct buffer_head *bh = NULL;
278 struct mmp_struct *mmp = NULL;
279 struct mmpd_data *mmpd_data;
280 u32 seq;
281 unsigned int mmp_check_interval = le16_to_cpu(es->s_mmp_update_interval);
282 unsigned int wait_time = 0;
283 int retval;
284
285 if (mmp_block < le32_to_cpu(es->s_first_data_block) ||
286 mmp_block >= ext4_blocks_count(es)) {
287 ext4_warning(sb, "Invalid MMP block in superblock");
288 goto failed;
289 }
290
291 retval = read_mmp_block(sb, &bh, mmp_block);
292 if (retval)
293 goto failed;
294
295 mmp = (struct mmp_struct *)(bh->b_data);
296
297 if (mmp_check_interval < EXT4_MMP_MIN_CHECK_INTERVAL)
298 mmp_check_interval = EXT4_MMP_MIN_CHECK_INTERVAL;
299
300 /*
301 * If check_interval in MMP block is larger, use that instead of
302 * update_interval from the superblock.
303 */
304 if (le16_to_cpu(mmp->mmp_check_interval) > mmp_check_interval)
305 mmp_check_interval = le16_to_cpu(mmp->mmp_check_interval);
306
307 seq = le32_to_cpu(mmp->mmp_seq);
308 if (seq == EXT4_MMP_SEQ_CLEAN)
309 goto skip;
310
311 if (seq == EXT4_MMP_SEQ_FSCK) {
312 dump_mmp_msg(sb, mmp, "fsck is running on the filesystem");
313 goto failed;
314 }
315
316 wait_time = min(mmp_check_interval * 2 + 1,
317 mmp_check_interval + 60);
318
319 /* Print MMP interval if more than 20 secs. */
320 if (wait_time > EXT4_MMP_MIN_CHECK_INTERVAL * 4)
321 ext4_warning(sb, "MMP interval %u higher than expected, please"
322 " wait.\n", wait_time * 2);
323
324 if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
325 ext4_warning(sb, "MMP startup interrupted, failing mount\n");
326 goto failed;
327 }
328
329 retval = read_mmp_block(sb, &bh, mmp_block);
330 if (retval)
331 goto failed;
332 mmp = (struct mmp_struct *)(bh->b_data);
333 if (seq != le32_to_cpu(mmp->mmp_seq)) {
334 dump_mmp_msg(sb, mmp,
335 "Device is already active on another node.");
336 goto failed;
337 }
338
339 skip:
340 /*
341 * write a new random sequence number.
342 */
343 seq = mmp_new_seq();
344 mmp->mmp_seq = cpu_to_le32(seq);
345
346 retval = write_mmp_block(sb, bh);
347 if (retval)
348 goto failed;
349
350 /*
351 * wait for MMP interval and check mmp_seq.
352 */
353 if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
354 ext4_warning(sb, "MMP startup interrupted, failing mount");
355 goto failed;
356 }
357
358 retval = read_mmp_block(sb, &bh, mmp_block);
359 if (retval)
360 goto failed;
361 mmp = (struct mmp_struct *)(bh->b_data);
362 if (seq != le32_to_cpu(mmp->mmp_seq)) {
363 dump_mmp_msg(sb, mmp,
364 "Device is already active on another node.");
365 goto failed;
366 }
367
368 mmpd_data = kmalloc(sizeof(*mmpd_data), GFP_KERNEL);
369 if (!mmpd_data) {
370 ext4_warning(sb, "not enough memory for mmpd_data");
371 goto failed;
372 }
373 mmpd_data->sb = sb;
374 mmpd_data->bh = bh;
375
376 /*
377 * Start a kernel thread to update the MMP block periodically.
378 */
379 EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, mmpd_data, "kmmpd-%.*s",
380 (int)sizeof(mmp->mmp_bdevname),
381 bdevname(bh->b_bdev,
382 mmp->mmp_bdevname));
383 if (IS_ERR(EXT4_SB(sb)->s_mmp_tsk)) {
384 EXT4_SB(sb)->s_mmp_tsk = NULL;
385 kfree(mmpd_data);
386 ext4_warning(sb, "Unable to create kmmpd thread for %s.",
387 sb->s_id);
388 goto failed;
389 }
390
391 return 0;
392
393 failed:
394 brelse(bh);
395 return 1;
396 }
397
398
399