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->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_feature_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_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 */
write_mmp_block_thawed(struct super_block * sb,struct buffer_head * bh)42 static 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
write_mmp_block(struct super_block * sb,struct buffer_head * bh)58 static int write_mmp_block(struct super_block *sb, struct buffer_head *bh)
59 {
60 /*
61 * We protect against freezing so that we don't create dirty buffers
62 * on frozen filesystem.
63 */
64 scoped_guard(super_write, sb)
65 return write_mmp_block_thawed(sb, bh);
66 }
67
68 /*
69 * Read the MMP block. It _must_ be read from disk and hence we clear the
70 * uptodate flag on the buffer.
71 */
read_mmp_block(struct super_block * sb,struct buffer_head ** bh,ext4_fsblk_t mmp_block)72 static int read_mmp_block(struct super_block *sb, struct buffer_head **bh,
73 ext4_fsblk_t mmp_block)
74 {
75 struct mmp_struct *mmp;
76 int ret;
77
78 if (*bh)
79 clear_buffer_uptodate(*bh);
80
81 /* This would be sb_bread(sb, mmp_block), except we need to be sure
82 * that the MD RAID device cache has been bypassed, and that the read
83 * is not blocked in the elevator. */
84 if (!*bh) {
85 *bh = sb_getblk(sb, mmp_block);
86 if (!*bh) {
87 ret = -ENOMEM;
88 goto warn_exit;
89 }
90 }
91
92 lock_buffer(*bh);
93 ret = ext4_read_bh(*bh, REQ_META | REQ_PRIO, NULL, false);
94 if (ret)
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 = data;
135 struct ext4_super_block *es = EXT4_SB(sb)->s_es;
136 struct buffer_head *bh = EXT4_SB(sb)->s_mmp_bh;
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 = 0;
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
158 memcpy(mmp->mmp_nodename, init_utsname()->nodename,
159 sizeof(mmp->mmp_nodename));
160
161 while (!kthread_should_stop() && !ext4_emergency_state(sb)) {
162 if (!ext4_has_feature_mmp(sb)) {
163 ext4_warning(sb, "kmmpd being stopped since MMP feature"
164 " has been disabled.");
165 goto wait_to_exit;
166 }
167 if (++seq > EXT4_MMP_SEQ_MAX)
168 seq = 1;
169
170 mmp->mmp_seq = cpu_to_le32(seq);
171 mmp->mmp_time = cpu_to_le64(ktime_get_real_seconds());
172 last_update_time = jiffies;
173
174 retval = write_mmp_block(sb, bh);
175 /*
176 * Don't spew too many error messages. Print one every
177 * (s_mmp_update_interval * 60) seconds.
178 */
179 if (retval) {
180 if ((failed_writes % 60) == 0) {
181 ext4_error_err(sb, -retval,
182 "Error writing to MMP block");
183 }
184 failed_writes++;
185 }
186
187 diff = jiffies - last_update_time;
188 if (diff < mmp_update_interval * HZ)
189 schedule_timeout_interruptible(mmp_update_interval *
190 HZ - diff);
191
192 /*
193 * We need to make sure that more than mmp_check_interval
194 * seconds have not passed since writing. If that has happened
195 * we need to check if the MMP block is as we left it.
196 */
197 diff = jiffies - last_update_time;
198 if (diff > mmp_check_interval * HZ) {
199 struct buffer_head *bh_check = NULL;
200 struct mmp_struct *mmp_check;
201
202 retval = read_mmp_block(sb, &bh_check, mmp_block);
203 if (retval) {
204 ext4_error_err(sb, -retval,
205 "error reading MMP data: %d",
206 retval);
207 goto wait_to_exit;
208 }
209
210 mmp_check = (struct mmp_struct *)(bh_check->b_data);
211 if (mmp->mmp_seq != mmp_check->mmp_seq ||
212 memcmp(mmp->mmp_nodename, mmp_check->mmp_nodename,
213 sizeof(mmp->mmp_nodename))) {
214 dump_mmp_msg(sb, mmp_check,
215 "Error while updating MMP info. "
216 "The filesystem seems to have been"
217 " multiply mounted.");
218 ext4_error_err(sb, EBUSY, "abort");
219 put_bh(bh_check);
220 retval = -EBUSY;
221 goto wait_to_exit;
222 }
223 put_bh(bh_check);
224 }
225
226 /*
227 * Adjust the mmp_check_interval depending on how much time
228 * it took for the MMP block to be written.
229 */
230 mmp_check_interval = clamp(EXT4_MMP_CHECK_MULT * diff / HZ,
231 EXT4_MMP_MIN_CHECK_INTERVAL,
232 EXT4_MMP_MAX_CHECK_INTERVAL);
233 mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
234 }
235
236 /*
237 * Unmount seems to be clean.
238 */
239 mmp->mmp_seq = cpu_to_le32(EXT4_MMP_SEQ_CLEAN);
240 mmp->mmp_time = cpu_to_le64(ktime_get_real_seconds());
241
242 retval = write_mmp_block(sb, bh);
243
244 wait_to_exit:
245 while (!kthread_should_stop()) {
246 set_current_state(TASK_INTERRUPTIBLE);
247 if (!kthread_should_stop())
248 schedule();
249 }
250 set_current_state(TASK_RUNNING);
251 return retval;
252 }
253
ext4_stop_mmpd(struct ext4_sb_info * sbi)254 void ext4_stop_mmpd(struct ext4_sb_info *sbi)
255 {
256 if (sbi->s_mmp_tsk) {
257 kthread_stop(sbi->s_mmp_tsk);
258 brelse(sbi->s_mmp_bh);
259 sbi->s_mmp_tsk = NULL;
260 }
261 }
262
263 /*
264 * Get a random new sequence number but make sure it is not greater than
265 * EXT4_MMP_SEQ_MAX.
266 */
mmp_new_seq(void)267 static unsigned int mmp_new_seq(void)
268 {
269 return get_random_u32_below(EXT4_MMP_SEQ_MAX + 1);
270 }
271
272 /*
273 * Protect the filesystem from being mounted more than once.
274 */
ext4_multi_mount_protect(struct super_block * sb,ext4_fsblk_t mmp_block)275 int ext4_multi_mount_protect(struct super_block *sb,
276 ext4_fsblk_t mmp_block)
277 {
278 struct ext4_super_block *es = EXT4_SB(sb)->s_es;
279 struct buffer_head *bh = NULL;
280 struct mmp_struct *mmp = NULL;
281 u32 seq;
282 unsigned int mmp_check_interval = le16_to_cpu(es->s_mmp_update_interval);
283 unsigned int wait_time = 0;
284 int retval;
285
286 if (mmp_block < le32_to_cpu(es->s_first_data_block) ||
287 mmp_block >= ext4_blocks_count(es)) {
288 ext4_warning(sb, "Invalid MMP block in superblock");
289 retval = -EINVAL;
290 goto failed;
291 }
292
293 retval = read_mmp_block(sb, &bh, mmp_block);
294 if (retval)
295 goto failed;
296
297 mmp = (struct mmp_struct *)(bh->b_data);
298
299 if (mmp_check_interval < EXT4_MMP_MIN_CHECK_INTERVAL)
300 mmp_check_interval = EXT4_MMP_MIN_CHECK_INTERVAL;
301
302 /*
303 * If check_interval in MMP block is larger, use that instead of
304 * update_interval from the superblock.
305 */
306 if (le16_to_cpu(mmp->mmp_check_interval) > mmp_check_interval)
307 mmp_check_interval = le16_to_cpu(mmp->mmp_check_interval);
308
309 seq = le32_to_cpu(mmp->mmp_seq);
310 if (seq == EXT4_MMP_SEQ_CLEAN)
311 goto skip;
312
313 if (seq == EXT4_MMP_SEQ_FSCK) {
314 dump_mmp_msg(sb, mmp, "fsck is running on the filesystem");
315 retval = -EBUSY;
316 goto failed;
317 }
318
319 wait_time = min(mmp_check_interval * 2 + 1,
320 mmp_check_interval + 60);
321
322 /* Print MMP interval if more than 20 secs. */
323 if (wait_time > EXT4_MMP_MIN_CHECK_INTERVAL * 4)
324 ext4_warning(sb, "MMP interval %u higher than expected, please"
325 " wait.\n", wait_time * 2);
326
327 if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
328 ext4_warning(sb, "MMP startup interrupted, failing mount\n");
329 retval = -ETIMEDOUT;
330 goto failed;
331 }
332
333 retval = read_mmp_block(sb, &bh, mmp_block);
334 if (retval)
335 goto failed;
336 mmp = (struct mmp_struct *)(bh->b_data);
337 if (seq != le32_to_cpu(mmp->mmp_seq)) {
338 dump_mmp_msg(sb, mmp,
339 "Device is already active on another node.");
340 retval = -EBUSY;
341 goto failed;
342 }
343
344 skip:
345 /*
346 * write a new random sequence number.
347 */
348 seq = mmp_new_seq();
349 mmp->mmp_seq = cpu_to_le32(seq);
350
351 /*
352 * On mount / remount we are protected against fs freezing (by s_umount
353 * semaphore) and grabbing freeze protection upsets lockdep
354 */
355 retval = write_mmp_block_thawed(sb, bh);
356 if (retval)
357 goto failed;
358
359 /*
360 * wait for MMP interval and check mmp_seq.
361 */
362 if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
363 ext4_warning(sb, "MMP startup interrupted, failing mount");
364 retval = -ETIMEDOUT;
365 goto failed;
366 }
367
368 retval = read_mmp_block(sb, &bh, mmp_block);
369 if (retval)
370 goto failed;
371 mmp = (struct mmp_struct *)(bh->b_data);
372 if (seq != le32_to_cpu(mmp->mmp_seq)) {
373 dump_mmp_msg(sb, mmp,
374 "Device is already active on another node.");
375 retval = -EBUSY;
376 goto failed;
377 }
378
379 EXT4_SB(sb)->s_mmp_bh = bh;
380
381 BUILD_BUG_ON(sizeof(mmp->mmp_bdevname) < BDEVNAME_SIZE);
382 snprintf(mmp->mmp_bdevname, sizeof(mmp->mmp_bdevname),
383 "%pg", bh->b_bdev);
384
385 /*
386 * Start a kernel thread to update the MMP block periodically.
387 */
388 EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, sb, "kmmpd-%.*s",
389 (int)sizeof(mmp->mmp_bdevname),
390 mmp->mmp_bdevname);
391 if (IS_ERR(EXT4_SB(sb)->s_mmp_tsk)) {
392 EXT4_SB(sb)->s_mmp_tsk = NULL;
393 ext4_warning(sb, "Unable to create kmmpd thread for %s.",
394 sb->s_id);
395 retval = -ENOMEM;
396 goto failed;
397 }
398
399 return 0;
400
401 failed:
402 brelse(bh);
403 return retval;
404 }
405