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dm crypt: fix cpu hotplug crash by removing per-cpu structure

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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>
Cc: stable@vger.kernel.org
This commit is contained in:
Mikulas Patocka 2014-02-20 18:01:01 -05:00 committed by Mike Snitzer
parent d6d211db37
commit 610f2de355
1 changed files with 12 additions and 49 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

61
drivers/md/dm-crypt.c
View File

@ -19,7 +19,6 @@
#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>
@ -43,6 +42,7 @@ struct convert_context {
struct bvec_iter iter_out;
sector_t cc_sector;
atomic_t cc_pending;
struct ablkcipher_request *req;
};
/*
@ -111,15 +111,7 @@ struct iv_tcw_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;
@ -150,12 +142,6 @@ 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;
@ -192,11 +178,6 @@ static void clone_init(struct dm_crypt_io *, struct bio *);
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.
*/
@ -903,16 +884,15 @@ static void kcryptd_async_done(struct crypto_async_request *async_req,
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));
}
/*
@ -921,7 +901,6 @@ static void crypt_alloc_req(struct crypt_config *cc,
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);
@ -932,7 +911,7 @@ static int crypt_convert(struct crypt_config *cc,
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 */
@ -941,7 +920,7 @@ static int crypt_convert(struct crypt_config *cc,
reinit_completion(&ctx->restart);
/* fall through*/
case -EINPROGRESS:
this_cc->req = NULL;
ctx->req = NULL;
ctx->cc_sector++;
continue;
@ -1040,6 +1019,7 @@ static struct dm_crypt_io *crypt_io_alloc(struct crypt_config *cc,
io->sector = sector;
io->error = 0;
io->base_io = NULL;
io->ctx.req = NULL;
atomic_set(&io->io_pending, 0);
return io;
@ -1065,6 +1045,8 @@ static void crypt_dec_pending(struct dm_crypt_io *io)
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))
@ -1492,8 +1474,6 @@ static int crypt_wipe_key(struct crypt_config *cc)
static void crypt_dtr(struct dm_target *ti)
{
struct crypt_config *cc = ti->private;
struct crypt_cpu *cpu_cc;
int cpu;
ti->private = NULL;
@ -1505,13 +1485,6 @@ static void crypt_dtr(struct dm_target *ti)
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)
@ -1530,9 +1503,6 @@ static void crypt_dtr(struct dm_target *ti)
if (cc->dev)
dm_put_device(ti, cc->dev);
if (cc->cpu)
free_percpu(cc->cpu);
kzfree(cc->cipher);
kzfree(cc->cipher_string);
@ -1588,13 +1558,6 @@ static int crypt_ctr_cipher(struct dm_target *ti,
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.