1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
|
===========================================
Fault injection capabilities infrastructure
===========================================
See also drivers/md/md-faulty.c and "every_nth" module option for scsi_debug.
Available fault injection capabilities
--------------------------------------
- failslab
injects slab allocation failures. (kmalloc(), kmem_cache_alloc(), ...)
- fail_page_alloc
injects page allocation failures. (alloc_pages(), get_free_pages(), ...)
- fail_usercopy
injects failures in user memory access functions. (copy_from_user(), get_user(), ...)
- fail_futex
injects futex deadlock and uaddr fault errors.
- fail_sunrpc
injects kernel RPC client and server failures.
- fail_make_request
injects disk IO errors on devices permitted by setting
/sys/block/<device>/make-it-fail or
/sys/block/<device>/<partition>/make-it-fail. (submit_bio_noacct())
- fail_mmc_request
injects MMC data errors on devices permitted by setting
debugfs entries under /sys/kernel/debug/mmc0/fail_mmc_request
- fail_function
injects error return on specific functions, which are marked by
ALLOW_ERROR_INJECTION() macro, by setting debugfs entries
under /sys/kernel/debug/fail_function. No boot option supported.
- fail_skb_realloc
inject skb (socket buffer) reallocation events into the network path. The
primary goal is to identify and prevent issues related to pointer
mismanagement in the network subsystem. By forcing skb reallocation at
strategic points, this feature creates scenarios where existing pointers to
skb headers become invalid.
When the fault is injected and the reallocation is triggered, cached pointers
to skb headers and data no longer reference valid memory locations. This
deliberate invalidation helps expose code paths where proper pointer updating
is neglected after a reallocation event.
By creating these controlled fault scenarios, the system can catch instances
where stale pointers are used, potentially leading to memory corruption or
system instability.
To select the interface to act on, write the network name to
/sys/kernel/debug/fail_skb_realloc/devname.
If this field is left empty (which is the default value), skb reallocation
will be forced on all network interfaces.
The effectiveness of this fault detection is enhanced when KASAN is
enabled, as it helps identify invalid memory references and use-after-free
(UAF) issues.
- NVMe fault injection
inject NVMe status code and retry flag on devices permitted by setting
debugfs entries under /sys/kernel/debug/nvme*/fault_inject. The default
status code is NVME_SC_INVALID_OPCODE with no retry. The status code and
retry flag can be set via the debugfs.
- Null test block driver fault injection
inject IO timeouts by setting config items under
/sys/kernel/config/nullb/<disk>/timeout_inject,
inject requeue requests by setting config items under
/sys/kernel/config/nullb/<disk>/requeue_inject, and
inject init_hctx() errors by setting config items under
/sys/kernel/config/nullb/<disk>/init_hctx_fault_inject.
Configure fault-injection capabilities behavior
-----------------------------------------------
debugfs entries
^^^^^^^^^^^^^^^
fault-inject-debugfs kernel module provides some debugfs entries for runtime
configuration of fault-injection capabilities.
- /sys/kernel/debug/fail*/probability:
likelihood of failure injection, in percent.
Format: <percent>
Note that one-failure-per-hundred is a very high error rate
for some testcases. Consider setting probability=100 and configure
/sys/kernel/debug/fail*/interval for such testcases.
- /sys/kernel/debug/fail*/interval:
specifies the interval between failures, for calls to
should_fail() that pass all the other tests.
Note that if you enable this, by setting interval>1, you will
probably want to set probability=100.
- /sys/kernel/debug/fail*/times:
specifies how many times failures may happen at most. A value of -1
means "no limit".
- /sys/kernel/debug/fail*/space:
specifies an initial resource "budget", decremented by "size"
on each call to should_fail(,size). Failure injection is
suppressed until "space" reaches zero.
- /sys/kernel/debug/fail*/verbose
Format: { 0 | 1 | 2 }
specifies the verbosity of the messages when failure is
injected. '0' means no messages; '1' will print only a single
log line per failure; '2' will print a call trace too -- useful
to debug the problems revealed by fault injection.
- /sys/kernel/debug/fail*/task-filter:
Format: { 'Y' | 'N' }
A value of 'N' disables filtering by process (default).
Any positive value limits failures to only processes indicated by
/proc/<pid>/make-it-fail==1.
- /sys/kernel/debug/fail*/require-start,
/sys/kernel/debug/fail*/require-end,
/sys/kernel/debug/fail*/reject-start,
/sys/kernel/debug/fail*/reject-end:
specifies the range of virtual addresses tested during
stacktrace walking. Failure is injected only if some caller
in the walked stacktrace lies within the required range, and
none lies within the rejected range.
Default required range is [0,ULONG_MAX) (whole of virtual address space).
Default rejected range is [0,0).
- /sys/kernel/debug/fail*/stacktrace-depth:
specifies the maximum stacktrace depth walked during search
for a caller within [require-start,require-end) OR
[reject-start,reject-end).
- /sys/kernel/debug/fail_page_alloc/ignore-gfp-highmem:
Format: { 'Y' | 'N' }
default is 'Y', setting it to 'N' will also inject failures into
highmem/user allocations (__GFP_HIGHMEM allocations).
- /sys/kernel/debug/failslab/cache-filter
Format: { 'Y' | 'N' }
default is 'N', setting it to 'Y' will only inject failures when
objects are requests from certain caches.
Select the cache by writing '1' to /sys/kernel/slab/<cache>/failslab:
- /sys/kernel/debug/failslab/ignore-gfp-wait:
- /sys/kernel/debug/fail_page_alloc/ignore-gfp-wait:
Format: { 'Y' | 'N' }
default is 'Y', setting it to 'N' will also inject failures
into allocations that can sleep (__GFP_DIRECT_RECLAIM allocations).
- /sys/kernel/debug/fail_page_alloc/min-order:
specifies the minimum page allocation order to be injected
failures.
- /sys/kernel/debug/fail_futex/ignore-private:
Format: { 'Y' | 'N' }
default is 'N', setting it to 'Y' will disable failure injections
when dealing with private (address space) futexes.
- /sys/kernel/debug/fail_sunrpc/ignore-client-disconnect:
Format: { 'Y' | 'N' }
default is 'N', setting it to 'Y' will disable disconnect
injection on the RPC client.
- /sys/kernel/debug/fail_sunrpc/ignore-server-disconnect:
Format: { 'Y' | 'N' }
default is 'N', setting it to 'Y' will disable disconnect
injection on the RPC server.
- /sys/kernel/debug/fail_sunrpc/ignore-cache-wait:
Format: { 'Y' | 'N' }
default is 'N', setting it to 'Y' will disable cache wait
injection on the RPC server.
- /sys/kernel/debug/fail_function/inject:
Format: { 'function-name' | '!function-name' | '' }
specifies the target function of error injection by name.
If the function name leads '!' prefix, given function is
removed from injection list. If nothing specified ('')
injection list is cleared.
- /sys/kernel/debug/fail_function/injectable:
(read only) shows error injectable functions and what type of
error values can be specified. The error type will be one of
below;
- NULL: retval must be 0.
- ERRNO: retval must be -1 to -MAX_ERRNO (-4096).
- ERR_NULL: retval must be 0 or -1 to -MAX_ERRNO (-4096).
- /sys/kernel/debug/fail_function/<function-name>/retval:
specifies the "error" return value to inject to the given function.
This will be created when the user specifies a new injection entry.
Note that this file only accepts unsigned values. So, if you want to
use a negative errno, you better use 'printf' instead of 'echo', e.g.:
$ printf %#x -12 > retval
- /sys/kernel/debug/fail_skb_realloc/devname:
Specifies the network interface on which to force SKB reallocation. If
left empty, SKB reallocation will be applied to all network interfaces.
Example usage::
# Force skb reallocation on eth0
echo "eth0" > /sys/kernel/debug/fail_skb_realloc/devname
# Clear the selection and force skb reallocation on all interfaces
echo "" > /sys/kernel/debug/fail_skb_realloc/devname
Boot option
^^^^^^^^^^^
In order to inject faults while debugfs is not available (early boot time),
use the boot option::
failslab=
fail_page_alloc=
fail_usercopy=
fail_make_request=
fail_futex=
fail_skb_realloc=
mmc_core.fail_request=<interval>,<probability>,<space>,<times>
proc entries
^^^^^^^^^^^^
- /proc/<pid>/fail-nth,
/proc/self/task/<tid>/fail-nth:
Write to this file of integer N makes N-th call in the task fail.
Read from this file returns a integer value. A value of '0' indicates
that the fault setup with a previous write to this file was injected.
A positive integer N indicates that the fault wasn't yet injected.
Note that this file enables all types of faults (slab, futex, etc).
This setting takes precedence over all other generic debugfs settings
like probability, interval, times, etc. But per-capability settings
(e.g. fail_futex/ignore-private) take precedence over it.
This feature is intended for systematic testing of faults in a single
system call. See an example below.
Error Injectable Functions
--------------------------
This part is for the kernel developers considering to add a function to
ALLOW_ERROR_INJECTION() macro.
Requirements for the Error Injectable Functions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Since the function-level error injection forcibly changes the code path
and returns an error even if the input and conditions are proper, this can
cause unexpected kernel crash if you allow error injection on the function
which is NOT error injectable. Thus, you (and reviewers) must ensure;
- The function returns an error code if it fails, and the callers must check
it correctly (need to recover from it).
- The function does not execute any code which can change any state before
the first error return. The state includes global or local, or input
variable. For example, clear output address storage (e.g. `*ret = NULL`),
increments/decrements counter, set a flag, preempt/irq disable or get
a lock (if those are recovered before returning error, that will be OK.)
The first requirement is important, and it will result in that the release
(free objects) functions are usually harder to inject errors than allocate
functions. If errors of such release functions are not correctly handled
it will cause a memory leak easily (the caller will confuse that the object
has been released or corrupted.)
The second one is for the caller which expects the function should always
does something. Thus if the function error injection skips whole of the
function, the expectation is betrayed and causes an unexpected error.
Type of the Error Injectable Functions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Each error injectable functions will have the error type specified by the
ALLOW_ERROR_INJECTION() macro. You have to choose it carefully if you add
a new error injectable function. If the wrong error type is chosen, the
kernel may crash because it may not be able to handle the error.
There are 4 types of errors defined in include/asm-generic/error-injection.h
EI_ETYPE_NULL
This function will return `NULL` if it fails. e.g. return an allocated
object address.
EI_ETYPE_ERRNO
This function will return an `-errno` error code if it fails. e.g. return
-EINVAL if the input is wrong. This will include the functions which will
return an address which encodes `-errno` by ERR_PTR() macro.
EI_ETYPE_ERRNO_NULL
This function will return an `-errno` or `NULL` if it fails. If the caller
of this function checks the return value with IS_ERR_OR_NULL() macro, this
type will be appropriate.
EI_ETYPE_TRUE
This function will return `true` (non-zero positive value) if it fails.
If you specifies a wrong type, for example, EI_TYPE_ERRNO for the function
which returns an allocated object, it may cause a problem because the returned
value is not an object address and the caller can not access to the address.
How to add new fault injection capability
-----------------------------------------
- #include <linux/fault-inject.h>
- define the fault attributes
DECLARE_FAULT_ATTR(name);
Please see the definition of struct fault_attr in fault-inject.h
for details.
- provide a way to configure fault attributes
- boot option
If you need to enable the fault injection capability from boot time, you can
provide boot option to configure it. There is a helper function for it:
setup_fault_attr(attr, str);
- debugfs entries
failslab, fail_page_alloc, fail_usercopy, and fail_make_request use this way.
Helper functions:
fault_create_debugfs_attr(name, parent, attr);
- module parameters
If the scope of the fault injection capability is limited to a
single kernel module, it is better to provide module parameters to
configure the fault attributes.
- add a hook to insert failures
Upon should_fail() returning true, client code should inject a failure:
should_fail(attr, size);
Application Examples
--------------------
- Inject slab allocation failures into module init/exit code::
#!/bin/bash
FAILTYPE=failslab
echo Y > /sys/kernel/debug/$FAILTYPE/task-filter
echo 10 > /sys/kernel/debug/$FAILTYPE/probability
echo 100 > /sys/kernel/debug/$FAILTYPE/interval
echo -1 > /sys/kernel/debug/$FAILTYPE/times
echo 0 > /sys/kernel/debug/$FAILTYPE/space
echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
echo Y > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
faulty_system()
{
bash -c "echo 1 > /proc/self/make-it-fail && exec $*"
}
if [ $# -eq 0 ]
then
echo "Usage: $0 modulename [ modulename ... ]"
exit 1
fi
for m in $*
do
echo inserting $m...
faulty_system modprobe $m
echo removing $m...
faulty_system modprobe -r $m
done
------------------------------------------------------------------------------
- Inject page allocation failures only for a specific module::
#!/bin/bash
FAILTYPE=fail_page_alloc
module=$1
if [ -z $module ]
then
echo "Usage: $0 <modulename>"
exit 1
fi
modprobe $module
if [ ! -d /sys/module/$module/sections ]
then
echo Module $module is not loaded
exit 1
fi
cat /sys/module/$module/sections/.text > /sys/kernel/debug/$FAILTYPE/require-start
cat /sys/module/$module/sections/.data > /sys/kernel/debug/$FAILTYPE/require-end
echo N > /sys/kernel/debug/$FAILTYPE/task-filter
echo 10 > /sys/kernel/debug/$FAILTYPE/probability
echo 100 > /sys/kernel/debug/$FAILTYPE/interval
echo -1 > /sys/kernel/debug/$FAILTYPE/times
echo 0 > /sys/kernel/debug/$FAILTYPE/space
echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
echo Y > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
echo Y > /sys/kernel/debug/$FAILTYPE/ignore-gfp-highmem
echo 10 > /sys/kernel/debug/$FAILTYPE/stacktrace-depth
trap "echo 0 > /sys/kernel/debug/$FAILTYPE/probability" SIGINT SIGTERM EXIT
echo "Injecting errors into the module $module... (interrupt to stop)"
sleep 1000000
------------------------------------------------------------------------------
- Inject open_ctree error while btrfs mount::
#!/bin/bash
rm -f testfile.img
dd if=/dev/zero of=testfile.img bs=1M seek=1000 count=1
DEVICE=$(losetup --show -f testfile.img)
mkfs.btrfs -f $DEVICE
mkdir -p tmpmnt
FAILTYPE=fail_function
FAILFUNC=open_ctree
echo $FAILFUNC > /sys/kernel/debug/$FAILTYPE/inject
printf %#x -12 > /sys/kernel/debug/$FAILTYPE/$FAILFUNC/retval
echo N > /sys/kernel/debug/$FAILTYPE/task-filter
echo 100 > /sys/kernel/debug/$FAILTYPE/probability
echo 0 > /sys/kernel/debug/$FAILTYPE/interval
echo -1 > /sys/kernel/debug/$FAILTYPE/times
echo 0 > /sys/kernel/debug/$FAILTYPE/space
echo 1 > /sys/kernel/debug/$FAILTYPE/verbose
mount -t btrfs $DEVICE tmpmnt
if [ $? -ne 0 ]
then
echo "SUCCESS!"
else
echo "FAILED!"
umount tmpmnt
fi
echo > /sys/kernel/debug/$FAILTYPE/inject
rmdir tmpmnt
losetup -d $DEVICE
rm testfile.img
------------------------------------------------------------------------------
- Inject only skbuff allocation failures ::
# mark skbuff_head_cache as faulty
echo 1 > /sys/kernel/slab/skbuff_head_cache/failslab
# Turn on cache filter (off by default)
echo 1 > /sys/kernel/debug/failslab/cache-filter
# Turn on fault injection
echo 1 > /sys/kernel/debug/failslab/times
echo 1 > /sys/kernel/debug/failslab/probability
Tool to run command with failslab or fail_page_alloc
----------------------------------------------------
In order to make it easier to accomplish the tasks mentioned above, we can use
tools/testing/fault-injection/failcmd.sh. Please run a command
"./tools/testing/fault-injection/failcmd.sh --help" for more information and
see the following examples.
Examples:
Run a command "make -C tools/testing/selftests/ run_tests" with injecting slab
allocation failure::
# ./tools/testing/fault-injection/failcmd.sh \
-- make -C tools/testing/selftests/ run_tests
Same as above except to specify 100 times failures at most instead of one time
at most by default::
# ./tools/testing/fault-injection/failcmd.sh --times=100 \
-- make -C tools/testing/selftests/ run_tests
Same as above except to inject page allocation failure instead of slab
allocation failure::
# env FAILCMD_TYPE=fail_page_alloc \
./tools/testing/fault-injection/failcmd.sh --times=100 \
-- make -C tools/testing/selftests/ run_tests
Systematic faults using fail-nth
---------------------------------
The following code systematically faults 0-th, 1-st, 2-nd and so on
capabilities in the socketpair() system call::
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/syscall.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
int main()
{
int i, err, res, fail_nth, fds[2];
char buf[128];
system("echo N > /sys/kernel/debug/failslab/ignore-gfp-wait");
sprintf(buf, "/proc/self/task/%ld/fail-nth", syscall(SYS_gettid));
fail_nth = open(buf, O_RDWR);
for (i = 1;; i++) {
sprintf(buf, "%d", i);
write(fail_nth, buf, strlen(buf));
res = socketpair(AF_LOCAL, SOCK_STREAM, 0, fds);
err = errno;
pread(fail_nth, buf, sizeof(buf), 0);
if (res == 0) {
close(fds[0]);
close(fds[1]);
}
printf("%d-th fault %c: res=%d/%d\n", i, atoi(buf) ? 'N' : 'Y',
res, err);
if (atoi(buf))
break;
}
return 0;
}
An example output::
1-th fault Y: res=-1/23
2-th fault Y: res=-1/23
3-th fault Y: res=-1/12
4-th fault Y: res=-1/12
5-th fault Y: res=-1/23
6-th fault Y: res=-1/23
7-th fault Y: res=-1/23
8-th fault Y: res=-1/12
9-th fault Y: res=-1/12
10-th fault Y: res=-1/12
11-th fault Y: res=-1/12
12-th fault Y: res=-1/12
13-th fault Y: res=-1/12
14-th fault Y: res=-1/12
15-th fault Y: res=-1/12
16-th fault N: res=0/12
|