[PATCH 3.10 090/103] dm crypt: fix cpu hotplug crash by removing per-cpu structure

Greg Kroah-Hartman
2014-06-04T23:25:53Z

From: Mikulas Patocka <mpatocka@redhat.com>

commit 610f2de3559c383caf8fbbf91e9968102dff7ca0 upstream.

The DM crypt target used per-cpu structures to hold pointers to a
ablkcipher_request structure. The code assumed that the work item keeps
executing on a single CPU, so it didn't use synchronization when
accessing this structure.

If a CPU is disabled by writing 0 to /sys/devices/system/cpu/cpu*/online,
the work item could be moved to another CPU. This causes dm-crypt
crashes, like the following, because the code starts using an incorrect
ablkcipher_request:

smpboot: CPU 7 is now offline
BUG: unable to handle kernel NULL pointer dereference at 0000000000000130
IP: [<ffffffffa1862b3d>] crypt_convert+0x12d/0x3c0 [dm_crypt]
...
Call Trace:
[<ffffffffa1864415>] ? kcryptd_crypt+0x305/0x470 [dm_crypt]
[<ffffffff81062060>] ? finish_task_switch+0x40/0xc0
[<ffffffff81052a28>] ? process_one_work+0x168/0x470
[<ffffffff8105366b>] ? worker_thread+0x10b/0x390
[<ffffffff81053560>] ? manage_workers.isra.26+0x290/0x290
[<ffffffff81058d9f>] ? kthread+0xaf/0xc0
[<ffffffff81058cf0>] ? kthread_create_on_node+0x120/0x120
[<ffffffff813464ac>] ? ret_from_fork+0x7c/0xb0
[<ffffffff81058cf0>] ? kthread_create_on_node+0x120/0x120

Fix this bug by removing the per-cpu definition. The structure
ablkcipher_request is accessed via a pointer from convert_context.
Consequently, if the work item is rescheduled to a different CPU, the
thread still uses the same ablkcipher_request.

This change may undermine performance improvements intended by commit
c0297721 ("dm crypt: scale to multiple cpus") on select hardware. In
practice no performance difference was observed on recent hardware. But
regardless, correctness is more important than performance.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/md/dm-crypt.c | 61 +++++++++-----------------------------------------
1 file changed, 12 insertions(+), 49 deletions(-)

--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -18,7 +18,6 @@
#include <linux/crypto.h>
#include <linux/workqueue.h>
#include <linux/backing-dev.h>
-#include <linux/percpu.h>
#include <linux/atomic.h>
#include <linux/scatterlist.h>
#include <asm/page.h>
@@ -44,6 +43,7 @@ struct convert_context {
unsigned int idx_out;
sector_t cc_sector;
atomic_t cc_pending;
+ struct ablkcipher_request *req;
};

/*
@@ -105,15 +105,7 @@ struct iv_lmk_private {
enum flags { DM_CRYPT_SUSPENDED, DM_CRYPT_KEY_VALID };

/*
- * Duplicated per-CPU state for cipher.
- */
-struct crypt_cpu {
- struct ablkcipher_request *req;
-};
-
-/*
- * The fields in here must be read only after initialization,
- * changing state should be in crypt_cpu.
+ * The fields in here must be read only after initialization.
*/
struct crypt_config {
struct dm_dev *dev;
@@ -143,12 +135,6 @@ struct crypt_config {
sector_t iv_offset;
unsigned int iv_size;

- /*
- * Duplicated per cpu state. Access through
- * per_cpu_ptr() only.
- */
- struct crypt_cpu __percpu *cpu;
-
/* ESSIV: struct crypto_cipher *essiv_tfm */
void *iv_private;
struct crypto_ablkcipher **tfms;
@@ -184,11 +170,6 @@ static void clone_init(struct dm_crypt_i
static void kcryptd_queue_crypt(struct dm_crypt_io *io);
static u8 *iv_of_dmreq(struct crypt_config *cc, struct dm_crypt_request *dmreq);

-static struct crypt_cpu *this_crypt_config(struct crypt_config *cc)
-{
- return this_cpu_ptr(cc->cpu);
-}
-
/*
* Use this to access cipher attributes that are the same for each CPU.
*/
@@ -738,16 +719,15 @@ static void kcryptd_async_done(struct cr
static void crypt_alloc_req(struct crypt_config *cc,
struct convert_context *ctx)
{
- struct crypt_cpu *this_cc = this_crypt_config(cc);
unsigned key_index = ctx->cc_sector & (cc->tfms_count - 1);

- if (!this_cc->req)
- this_cc->req = mempool_alloc(cc->req_pool, GFP_NOIO);
+ if (!ctx->req)
+ ctx->req = mempool_alloc(cc->req_pool, GFP_NOIO);

- ablkcipher_request_set_tfm(this_cc->req, cc->tfms[key_index]);
- ablkcipher_request_set_callback(this_cc->req,
+ ablkcipher_request_set_tfm(ctx->req, cc->tfms[key_index]);
+ ablkcipher_request_set_callback(ctx->req,
CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
- kcryptd_async_done, dmreq_of_req(cc, this_cc->req));
+ kcryptd_async_done, dmreq_of_req(cc, ctx->req));
}

/*
@@ -756,7 +736,6 @@ static void crypt_alloc_req(struct crypt
static int crypt_convert(struct crypt_config *cc,
struct convert_context *ctx)
{
- struct crypt_cpu *this_cc = this_crypt_config(cc);
int r;

atomic_set(&ctx->cc_pending, 1);
@@ -768,7 +747,7 @@ static int crypt_convert(struct crypt_co

atomic_inc(&ctx->cc_pending);

- r = crypt_convert_block(cc, ctx, this_cc->req);
+ r = crypt_convert_block(cc, ctx, ctx->req);

switch (r) {
/* async */
@@ -777,7 +756,7 @@ static int crypt_convert(struct crypt_co
INIT_COMPLETION(ctx->restart);
/* fall through*/
case -EINPROGRESS:
- this_cc->req = NULL;
+ ctx->req = NULL;
ctx->cc_sector++;
continue;

@@ -876,6 +855,7 @@ static struct dm_crypt_io *crypt_io_allo
io->sector = sector;
io->error = 0;
io->base_io = NULL;
+ io->ctx.req = NULL;
atomic_set(&io->io_pending, 0);

return io;
@@ -901,6 +881,8 @@ static void crypt_dec_pending(struct dm_
if (!atomic_dec_and_test(&io->io_pending))
return;

+ if (io->ctx.req)
+ mempool_free(io->ctx.req, cc->req_pool);
mempool_free(io, cc->io_pool);

if (likely(!base_io))
@@ -1326,8 +1308,6 @@ static int crypt_wipe_key(struct crypt_c
static void crypt_dtr(struct dm_target *ti)
{
struct crypt_config *cc = ti->private;
- struct crypt_cpu *cpu_cc;
- int cpu;

ti->private = NULL;

@@ -1339,13 +1319,6 @@ static void crypt_dtr(struct dm_target *
if (cc->crypt_queue)
destroy_workqueue(cc->crypt_queue);

- if (cc->cpu)
- for_each_possible_cpu(cpu) {
- cpu_cc = per_cpu_ptr(cc->cpu, cpu);
- if (cpu_cc->req)
- mempool_free(cpu_cc->req, cc->req_pool);
- }
-
crypt_free_tfms(cc);

if (cc->bs)
@@ -1364,9 +1337,6 @@ static void crypt_dtr(struct dm_target *
if (cc->dev)
dm_put_device(ti, cc->dev);

- if (cc->cpu)
- free_percpu(cc->cpu);
-
kzfree(cc->cipher);
kzfree(cc->cipher_string);

@@ -1421,13 +1391,6 @@ static int crypt_ctr_cipher(struct dm_ta
if (tmp)
DMWARN("Ignoring unexpected additional cipher options");

- cc->cpu = __alloc_percpu(sizeof(*(cc->cpu)),
- __alignof__(struct crypt_cpu));
- if (!cc->cpu) {
- ti->error = "Cannot allocate per cpu state";
- goto bad_mem;
- }
-
/*
* For compatibility with the original dm-crypt mapping format, if
* only the cipher name is supplied, use cbc-plain.