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 -EIO;
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 lock_buffer(*bh);
89 ret = ext4_read_bh(*bh, REQ_META | REQ_PRIO, NULL);
90 if (ret)
91 goto warn_exit;
92
93 mmp = (struct mmp_struct *)((*bh)->b_data);
94 if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC) {
95 ret = -EFSCORRUPTED;
96 goto warn_exit;
97 }
98 if (!ext4_mmp_csum_verify(sb, mmp)) {
99 ret = -EFSBADCRC;
100 goto warn_exit;
101 }
102 return 0;
103 warn_exit:
104 brelse(*bh);
105 *bh = NULL;
106 ext4_warning(sb, "Error %d while reading MMP block %llu",
107 ret, mmp_block);
108 return ret;
109 }
110
111 /*
112 * Dump as much information as possible to help the admin.
113 */
__dump_mmp_msg(struct super_block * sb,struct mmp_struct * mmp,const char * function,unsigned int line,const char * msg)114 void __dump_mmp_msg(struct super_block *sb, struct mmp_struct *mmp,
115 const char *function, unsigned int line, const char *msg)
116 {
117 __ext4_warning(sb, function, line, "%s", msg);
118 __ext4_warning(sb, function, line,
119 "MMP failure info: last update time: %llu, last update node: %.*s, last update device: %.*s",
120 (unsigned long long)le64_to_cpu(mmp->mmp_time),
121 (int)sizeof(mmp->mmp_nodename), mmp->mmp_nodename,
122 (int)sizeof(mmp->mmp_bdevname), mmp->mmp_bdevname);
123 }
124
125 /*
126 * kmmpd will update the MMP sequence every s_mmp_update_interval seconds
127 */
kmmpd(void * data)128 static int kmmpd(void *data)
129 {
130 struct super_block *sb = (struct super_block *) data;
131 struct ext4_super_block *es = EXT4_SB(sb)->s_es;
132 struct buffer_head *bh = EXT4_SB(sb)->s_mmp_bh;
133 struct mmp_struct *mmp;
134 ext4_fsblk_t mmp_block;
135 u32 seq = 0;
136 unsigned long failed_writes = 0;
137 int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval);
138 unsigned mmp_check_interval;
139 unsigned long last_update_time;
140 unsigned long diff;
141 int retval = 0;
142
143 mmp_block = le64_to_cpu(es->s_mmp_block);
144 mmp = (struct mmp_struct *)(bh->b_data);
145 mmp->mmp_time = cpu_to_le64(ktime_get_real_seconds());
146 /*
147 * Start with the higher mmp_check_interval and reduce it if
148 * the MMP block is being updated on time.
149 */
150 mmp_check_interval = max(EXT4_MMP_CHECK_MULT * mmp_update_interval,
151 EXT4_MMP_MIN_CHECK_INTERVAL);
152 mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
153 BUILD_BUG_ON(sizeof(mmp->mmp_bdevname) < BDEVNAME_SIZE);
154 bdevname(bh->b_bdev, mmp->mmp_bdevname);
155
156 memcpy(mmp->mmp_nodename, init_utsname()->nodename,
157 sizeof(mmp->mmp_nodename));
158
159 while (!kthread_should_stop() && !sb_rdonly(sb)) {
160 if (!ext4_has_feature_mmp(sb)) {
161 ext4_warning(sb, "kmmpd being stopped since MMP feature"
162 " has been disabled.");
163 goto wait_to_exit;
164 }
165 if (++seq > EXT4_MMP_SEQ_MAX)
166 seq = 1;
167
168 mmp->mmp_seq = cpu_to_le32(seq);
169 mmp->mmp_time = cpu_to_le64(ktime_get_real_seconds());
170 last_update_time = jiffies;
171
172 retval = write_mmp_block(sb, bh);
173 /*
174 * Don't spew too many error messages. Print one every
175 * (s_mmp_update_interval * 60) seconds.
176 */
177 if (retval) {
178 if ((failed_writes % 60) == 0) {
179 ext4_error_err(sb, -retval,
180 "Error writing to MMP block");
181 }
182 failed_writes++;
183 }
184
185 diff = jiffies - last_update_time;
186 if (diff < mmp_update_interval * HZ)
187 schedule_timeout_interruptible(mmp_update_interval *
188 HZ - diff);
189
190 /*
191 * We need to make sure that more than mmp_check_interval
192 * seconds have not passed since writing. If that has happened
193 * we need to check if the MMP block is as we left it.
194 */
195 diff = jiffies - last_update_time;
196 if (diff > mmp_check_interval * HZ) {
197 struct buffer_head *bh_check = NULL;
198 struct mmp_struct *mmp_check;
199
200 retval = read_mmp_block(sb, &bh_check, mmp_block);
201 if (retval) {
202 ext4_error_err(sb, -retval,
203 "error reading MMP data: %d",
204 retval);
205 goto wait_to_exit;
206 }
207
208 mmp_check = (struct mmp_struct *)(bh_check->b_data);
209 if (mmp->mmp_seq != mmp_check->mmp_seq ||
210 memcmp(mmp->mmp_nodename, mmp_check->mmp_nodename,
211 sizeof(mmp->mmp_nodename))) {
212 dump_mmp_msg(sb, mmp_check,
213 "Error while updating MMP info. "
214 "The filesystem seems to have been"
215 " multiply mounted.");
216 ext4_error_err(sb, EBUSY, "abort");
217 put_bh(bh_check);
218 retval = -EBUSY;
219 goto wait_to_exit;
220 }
221 put_bh(bh_check);
222 }
223
224 /*
225 * Adjust the mmp_check_interval depending on how much time
226 * it took for the MMP block to be written.
227 */
228 mmp_check_interval = max(min(EXT4_MMP_CHECK_MULT * diff / HZ,
229 EXT4_MMP_MAX_CHECK_INTERVAL),
230 EXT4_MMP_MIN_CHECK_INTERVAL);
231 mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
232 }
233
234 /*
235 * Unmount seems to be clean.
236 */
237 mmp->mmp_seq = cpu_to_le32(EXT4_MMP_SEQ_CLEAN);
238 mmp->mmp_time = cpu_to_le64(ktime_get_real_seconds());
239
240 retval = write_mmp_block(sb, bh);
241
242 wait_to_exit:
243 while (!kthread_should_stop()) {
244 set_current_state(TASK_INTERRUPTIBLE);
245 if (!kthread_should_stop())
246 schedule();
247 }
248 set_current_state(TASK_RUNNING);
249 return retval;
250 }
251
ext4_stop_mmpd(struct ext4_sb_info * sbi)252 void ext4_stop_mmpd(struct ext4_sb_info *sbi)
253 {
254 if (sbi->s_mmp_tsk) {
255 kthread_stop(sbi->s_mmp_tsk);
256 brelse(sbi->s_mmp_bh);
257 sbi->s_mmp_tsk = NULL;
258 }
259 }
260
261 /*
262 * Get a random new sequence number but make sure it is not greater than
263 * EXT4_MMP_SEQ_MAX.
264 */
mmp_new_seq(void)265 static unsigned int mmp_new_seq(void)
266 {
267 u32 new_seq;
268
269 do {
270 new_seq = prandom_u32();
271 } while (new_seq > EXT4_MMP_SEQ_MAX);
272
273 return new_seq;
274 }
275
276 /*
277 * Protect the filesystem from being mounted more than once.
278 */
ext4_multi_mount_protect(struct super_block * sb,ext4_fsblk_t mmp_block)279 int 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 goto failed;
294 }
295
296 retval = read_mmp_block(sb, &bh, mmp_block);
297 if (retval)
298 goto failed;
299
300 mmp = (struct mmp_struct *)(bh->b_data);
301
302 if (mmp_check_interval < EXT4_MMP_MIN_CHECK_INTERVAL)
303 mmp_check_interval = EXT4_MMP_MIN_CHECK_INTERVAL;
304
305 /*
306 * If check_interval in MMP block is larger, use that instead of
307 * update_interval from the superblock.
308 */
309 if (le16_to_cpu(mmp->mmp_check_interval) > mmp_check_interval)
310 mmp_check_interval = le16_to_cpu(mmp->mmp_check_interval);
311
312 seq = le32_to_cpu(mmp->mmp_seq);
313 if (seq == EXT4_MMP_SEQ_CLEAN)
314 goto skip;
315
316 if (seq == EXT4_MMP_SEQ_FSCK) {
317 dump_mmp_msg(sb, mmp, "fsck is running on the filesystem");
318 goto failed;
319 }
320
321 wait_time = min(mmp_check_interval * 2 + 1,
322 mmp_check_interval + 60);
323
324 /* Print MMP interval if more than 20 secs. */
325 if (wait_time > EXT4_MMP_MIN_CHECK_INTERVAL * 4)
326 ext4_warning(sb, "MMP interval %u higher than expected, please"
327 " wait.\n", wait_time * 2);
328
329 if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
330 ext4_warning(sb, "MMP startup interrupted, failing mount\n");
331 goto failed;
332 }
333
334 retval = read_mmp_block(sb, &bh, mmp_block);
335 if (retval)
336 goto failed;
337 mmp = (struct mmp_struct *)(bh->b_data);
338 if (seq != le32_to_cpu(mmp->mmp_seq)) {
339 dump_mmp_msg(sb, mmp,
340 "Device is already active on another node.");
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 retval = write_mmp_block(sb, bh);
352 if (retval)
353 goto failed;
354
355 /*
356 * wait for MMP interval and check mmp_seq.
357 */
358 if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
359 ext4_warning(sb, "MMP startup interrupted, failing mount");
360 goto failed;
361 }
362
363 retval = read_mmp_block(sb, &bh, mmp_block);
364 if (retval)
365 goto failed;
366 mmp = (struct mmp_struct *)(bh->b_data);
367 if (seq != le32_to_cpu(mmp->mmp_seq)) {
368 dump_mmp_msg(sb, mmp,
369 "Device is already active on another node.");
370 goto failed;
371 }
372
373 EXT4_SB(sb)->s_mmp_bh = bh;
374
375 /*
376 * Start a kernel thread to update the MMP block periodically.
377 */
378 EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, sb, "kmmpd-%.*s",
379 (int)sizeof(mmp->mmp_bdevname),
380 bdevname(bh->b_bdev,
381 mmp->mmp_bdevname));
382 if (IS_ERR(EXT4_SB(sb)->s_mmp_tsk)) {
383 EXT4_SB(sb)->s_mmp_tsk = NULL;
384 ext4_warning(sb, "Unable to create kmmpd thread for %s.",
385 sb->s_id);
386 goto failed;
387 }
388
389 return 0;
390
391 failed:
392 brelse(bh);
393 return 1;
394 }
395