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 */
11static __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(crc: sbi->s_csum_seed, address: (char *)mmp, length: offset);
18
19 return cpu_to_le32(csum);
20}
21
22static int ext4_mmp_csum_verify(struct super_block *sb, struct mmp_struct *mmp)
23{
24 if (!ext4_has_feature_metadata_csum(sb))
25 return 1;
26
27 return mmp->mmp_checksum == ext4_mmp_csum(sb, mmp);
28}
29
30static void ext4_mmp_csum_set(struct super_block *sb, struct mmp_struct *mmp)
31{
32 if (!ext4_has_feature_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 */
42static int write_mmp_block_thawed(struct super_block *sb,
43 struct buffer_head *bh)
44{
45 struct mmp_struct *mmp = (struct mmp_struct *)(bh->b_data);
46
47 ext4_mmp_csum_set(sb, mmp);
48 lock_buffer(bh);
49 bh->b_end_io = end_buffer_write_sync;
50 get_bh(bh);
51 submit_bh(REQ_OP_WRITE | REQ_SYNC | REQ_META | REQ_PRIO, bh);
52 wait_on_buffer(bh);
53 if (unlikely(!buffer_uptodate(bh)))
54 return -EIO;
55 return 0;
56}
57
58static int write_mmp_block(struct super_block *sb, struct buffer_head *bh)
59{
60 int err;
61
62 /*
63 * We protect against freezing so that we don't create dirty buffers
64 * on frozen filesystem.
65 */
66 sb_start_write(sb);
67 err = write_mmp_block_thawed(sb, bh);
68 sb_end_write(sb);
69 return err;
70}
71
72/*
73 * Read the MMP block. It _must_ be read from disk and hence we clear the
74 * uptodate flag on the buffer.
75 */
76static int read_mmp_block(struct super_block *sb, struct buffer_head **bh,
77 ext4_fsblk_t mmp_block)
78{
79 struct mmp_struct *mmp;
80 int ret;
81
82 if (*bh)
83 clear_buffer_uptodate(bh: *bh);
84
85 /* This would be sb_bread(sb, mmp_block), except we need to be sure
86 * that the MD RAID device cache has been bypassed, and that the read
87 * is not blocked in the elevator. */
88 if (!*bh) {
89 *bh = sb_getblk(sb, block: mmp_block);
90 if (!*bh) {
91 ret = -ENOMEM;
92 goto warn_exit;
93 }
94 }
95
96 lock_buffer(bh: *bh);
97 ret = ext4_read_bh(bh: *bh, REQ_META | REQ_PRIO, NULL, simu_fail: false);
98 if (ret)
99 goto warn_exit;
100
101 mmp = (struct mmp_struct *)((*bh)->b_data);
102 if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC) {
103 ret = -EFSCORRUPTED;
104 goto warn_exit;
105 }
106 if (!ext4_mmp_csum_verify(sb, mmp)) {
107 ret = -EFSBADCRC;
108 goto warn_exit;
109 }
110 return 0;
111warn_exit:
112 brelse(bh: *bh);
113 *bh = NULL;
114 ext4_warning(sb, "Error %d while reading MMP block %llu",
115 ret, mmp_block);
116 return ret;
117}
118
119/*
120 * Dump as much information as possible to help the admin.
121 */
122void __dump_mmp_msg(struct super_block *sb, struct mmp_struct *mmp,
123 const char *function, unsigned int line, const char *msg)
124{
125 __ext4_warning(sb, function, line, "%s", msg);
126 __ext4_warning(sb, function, line,
127 "MMP failure info: last update time: %llu, last update node: %.*s, last update device: %.*s",
128 (unsigned long long)le64_to_cpu(mmp->mmp_time),
129 (int)sizeof(mmp->mmp_nodename), mmp->mmp_nodename,
130 (int)sizeof(mmp->mmp_bdevname), mmp->mmp_bdevname);
131}
132
133/*
134 * kmmpd will update the MMP sequence every s_mmp_update_interval seconds
135 */
136static int kmmpd(void *data)
137{
138 struct super_block *sb = data;
139 struct ext4_super_block *es = EXT4_SB(sb)->s_es;
140 struct buffer_head *bh = EXT4_SB(sb)->s_mmp_bh;
141 struct mmp_struct *mmp;
142 ext4_fsblk_t mmp_block;
143 u32 seq = 0;
144 unsigned long failed_writes = 0;
145 int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval);
146 unsigned mmp_check_interval;
147 unsigned long last_update_time;
148 unsigned long diff;
149 int retval = 0;
150
151 mmp_block = le64_to_cpu(es->s_mmp_block);
152 mmp = (struct mmp_struct *)(bh->b_data);
153 mmp->mmp_time = cpu_to_le64(ktime_get_real_seconds());
154 /*
155 * Start with the higher mmp_check_interval and reduce it if
156 * the MMP block is being updated on time.
157 */
158 mmp_check_interval = max(EXT4_MMP_CHECK_MULT * mmp_update_interval,
159 EXT4_MMP_MIN_CHECK_INTERVAL);
160 mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
161
162 memcpy(to: mmp->mmp_nodename, from: init_utsname()->nodename,
163 len: sizeof(mmp->mmp_nodename));
164
165 while (!kthread_should_stop() && !ext4_emergency_state(sb)) {
166 if (!ext4_has_feature_mmp(sb)) {
167 ext4_warning(sb, "kmmpd being stopped since MMP feature"
168 " has been disabled.");
169 goto wait_to_exit;
170 }
171 if (++seq > EXT4_MMP_SEQ_MAX)
172 seq = 1;
173
174 mmp->mmp_seq = cpu_to_le32(seq);
175 mmp->mmp_time = cpu_to_le64(ktime_get_real_seconds());
176 last_update_time = jiffies;
177
178 retval = write_mmp_block(sb, bh);
179 /*
180 * Don't spew too many error messages. Print one every
181 * (s_mmp_update_interval * 60) seconds.
182 */
183 if (retval) {
184 if ((failed_writes % 60) == 0) {
185 ext4_error_err(sb, -retval,
186 "Error writing to MMP block");
187 }
188 failed_writes++;
189 }
190
191 diff = jiffies - last_update_time;
192 if (diff < mmp_update_interval * HZ)
193 schedule_timeout_interruptible(timeout: mmp_update_interval *
194 HZ - diff);
195
196 /*
197 * We need to make sure that more than mmp_check_interval
198 * seconds have not passed since writing. If that has happened
199 * we need to check if the MMP block is as we left it.
200 */
201 diff = jiffies - last_update_time;
202 if (diff > mmp_check_interval * HZ) {
203 struct buffer_head *bh_check = NULL;
204 struct mmp_struct *mmp_check;
205
206 retval = read_mmp_block(sb, bh: &bh_check, mmp_block);
207 if (retval) {
208 ext4_error_err(sb, -retval,
209 "error reading MMP data: %d",
210 retval);
211 goto wait_to_exit;
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_err(sb, EBUSY, "abort");
223 put_bh(bh: bh_check);
224 retval = -EBUSY;
225 goto wait_to_exit;
226 }
227 put_bh(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 = clamp(EXT4_MMP_CHECK_MULT * diff / HZ,
235 EXT4_MMP_MIN_CHECK_INTERVAL,
236 EXT4_MMP_MAX_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
248wait_to_exit:
249 while (!kthread_should_stop()) {
250 set_current_state(TASK_INTERRUPTIBLE);
251 if (!kthread_should_stop())
252 schedule();
253 }
254 set_current_state(TASK_RUNNING);
255 return retval;
256}
257
258void ext4_stop_mmpd(struct ext4_sb_info *sbi)
259{
260 if (sbi->s_mmp_tsk) {
261 kthread_stop(k: sbi->s_mmp_tsk);
262 brelse(bh: sbi->s_mmp_bh);
263 sbi->s_mmp_tsk = NULL;
264 }
265}
266
267/*
268 * Get a random new sequence number but make sure it is not greater than
269 * EXT4_MMP_SEQ_MAX.
270 */
271static unsigned int mmp_new_seq(void)
272{
273 return get_random_u32_below(EXT4_MMP_SEQ_MAX + 1);
274}
275
276/*
277 * Protect the filesystem from being mounted more than once.
278 */
279int ext4_multi_mount_protect(struct super_block *sb,
280 ext4_fsblk_t mmp_block)
281{
282 struct ext4_super_block *es = EXT4_SB(sb)->s_es;
283 struct buffer_head *bh = NULL;
284 struct mmp_struct *mmp = NULL;
285 u32 seq;
286 unsigned int mmp_check_interval = le16_to_cpu(es->s_mmp_update_interval);
287 unsigned int wait_time = 0;
288 int retval;
289
290 if (mmp_block < le32_to_cpu(es->s_first_data_block) ||
291 mmp_block >= ext4_blocks_count(es)) {
292 ext4_warning(sb, "Invalid MMP block in superblock");
293 retval = -EINVAL;
294 goto failed;
295 }
296
297 retval = read_mmp_block(sb, bh: &bh, mmp_block);
298 if (retval)
299 goto failed;
300
301 mmp = (struct mmp_struct *)(bh->b_data);
302
303 if (mmp_check_interval < EXT4_MMP_MIN_CHECK_INTERVAL)
304 mmp_check_interval = EXT4_MMP_MIN_CHECK_INTERVAL;
305
306 /*
307 * If check_interval in MMP block is larger, use that instead of
308 * update_interval from the superblock.
309 */
310 if (le16_to_cpu(mmp->mmp_check_interval) > mmp_check_interval)
311 mmp_check_interval = le16_to_cpu(mmp->mmp_check_interval);
312
313 seq = le32_to_cpu(mmp->mmp_seq);
314 if (seq == EXT4_MMP_SEQ_CLEAN)
315 goto skip;
316
317 if (seq == EXT4_MMP_SEQ_FSCK) {
318 dump_mmp_msg(sb, mmp, "fsck is running on the filesystem");
319 retval = -EBUSY;
320 goto failed;
321 }
322
323 wait_time = min(mmp_check_interval * 2 + 1,
324 mmp_check_interval + 60);
325
326 /* Print MMP interval if more than 20 secs. */
327 if (wait_time > EXT4_MMP_MIN_CHECK_INTERVAL * 4)
328 ext4_warning(sb, "MMP interval %u higher than expected, please"
329 " wait.\n", wait_time * 2);
330
331 if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
332 ext4_warning(sb, "MMP startup interrupted, failing mount\n");
333 retval = -ETIMEDOUT;
334 goto failed;
335 }
336
337 retval = read_mmp_block(sb, bh: &bh, mmp_block);
338 if (retval)
339 goto failed;
340 mmp = (struct mmp_struct *)(bh->b_data);
341 if (seq != le32_to_cpu(mmp->mmp_seq)) {
342 dump_mmp_msg(sb, mmp,
343 "Device is already active on another node.");
344 retval = -EBUSY;
345 goto failed;
346 }
347
348skip:
349 /*
350 * write a new random sequence number.
351 */
352 seq = mmp_new_seq();
353 mmp->mmp_seq = cpu_to_le32(seq);
354
355 /*
356 * On mount / remount we are protected against fs freezing (by s_umount
357 * semaphore) and grabbing freeze protection upsets lockdep
358 */
359 retval = write_mmp_block_thawed(sb, bh);
360 if (retval)
361 goto failed;
362
363 /*
364 * wait for MMP interval and check mmp_seq.
365 */
366 if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
367 ext4_warning(sb, "MMP startup interrupted, failing mount");
368 retval = -ETIMEDOUT;
369 goto failed;
370 }
371
372 retval = read_mmp_block(sb, bh: &bh, mmp_block);
373 if (retval)
374 goto failed;
375 mmp = (struct mmp_struct *)(bh->b_data);
376 if (seq != le32_to_cpu(mmp->mmp_seq)) {
377 dump_mmp_msg(sb, mmp,
378 "Device is already active on another node.");
379 retval = -EBUSY;
380 goto failed;
381 }
382
383 EXT4_SB(sb)->s_mmp_bh = bh;
384
385 BUILD_BUG_ON(sizeof(mmp->mmp_bdevname) < BDEVNAME_SIZE);
386 snprintf(buf: mmp->mmp_bdevname, size: sizeof(mmp->mmp_bdevname),
387 fmt: "%pg", bh->b_bdev);
388
389 /*
390 * Start a kernel thread to update the MMP block periodically.
391 */
392 EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, sb, "kmmpd-%.*s",
393 (int)sizeof(mmp->mmp_bdevname),
394 mmp->mmp_bdevname);
395 if (IS_ERR(ptr: EXT4_SB(sb)->s_mmp_tsk)) {
396 EXT4_SB(sb)->s_mmp_tsk = NULL;
397 ext4_warning(sb, "Unable to create kmmpd thread for %s.",
398 sb->s_id);
399 retval = -ENOMEM;
400 goto failed;
401 }
402
403 return 0;
404
405failed:
406 brelse(bh);
407 return retval;
408}
409