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

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

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 784695d..53b2132 100644 (file)
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -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.