diff options
authorOmar Sandoval <osandov@fb.com>2021-05-10 17:05:35 -0700
committerJens Axboe <axboe@kernel.dk>2021-05-11 08:12:14 -0600
commitefed9a3337e341bd0989161b97453b52567bc59d (patch)
parent63c8af5687f6b1b70e9458cac1ffb25e86db1695 (diff)
kyber: fix out of bounds access when preempted
__blk_mq_sched_bio_merge() gets the ctx and hctx for the current CPU and passes the hctx to ->bio_merge(). kyber_bio_merge() then gets the ctx for the current CPU again and uses that to get the corresponding Kyber context in the passed hctx. However, the thread may be preempted between the two calls to blk_mq_get_ctx(), and the ctx returned the second time may no longer correspond to the passed hctx. This "works" accidentally most of the time, but it can cause us to read garbage if the second ctx came from an hctx with more ctx's than the first one (i.e., if ctx->index_hw[hctx->type] > hctx->nr_ctx). This manifested as this UBSAN array index out of bounds error reported by Jakub: UBSAN: array-index-out-of-bounds in ../kernel/locking/qspinlock.c:130:9 index 13106 is out of range for type 'long unsigned int [128]' Call Trace: dump_stack+0xa4/0xe5 ubsan_epilogue+0x5/0x40 __ubsan_handle_out_of_bounds.cold.13+0x2a/0x34 queued_spin_lock_slowpath+0x476/0x480 do_raw_spin_lock+0x1c2/0x1d0 kyber_bio_merge+0x112/0x180 blk_mq_submit_bio+0x1f5/0x1100 submit_bio_noacct+0x7b0/0x870 submit_bio+0xc2/0x3a0 btrfs_map_bio+0x4f0/0x9d0 btrfs_submit_data_bio+0x24e/0x310 submit_one_bio+0x7f/0xb0 submit_extent_page+0xc4/0x440 __extent_writepage_io+0x2b8/0x5e0 __extent_writepage+0x28d/0x6e0 extent_write_cache_pages+0x4d7/0x7a0 extent_writepages+0xa2/0x110 do_writepages+0x8f/0x180 __writeback_single_inode+0x99/0x7f0 writeback_sb_inodes+0x34e/0x790 __writeback_inodes_wb+0x9e/0x120 wb_writeback+0x4d2/0x660 wb_workfn+0x64d/0xa10 process_one_work+0x53a/0xa80 worker_thread+0x69/0x5b0 kthread+0x20b/0x240 ret_from_fork+0x1f/0x30 Only Kyber uses the hctx, so fix it by passing the request_queue to ->bio_merge() instead. BFQ and mq-deadline just use that, and Kyber can map the queues itself to avoid the mismatch. Fixes: a6088845c2bf ("block: kyber: make kyber more friendly with merging") Reported-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Omar Sandoval <osandov@fb.com> Link: https://lore.kernel.org/r/c7598605401a48d5cfeadebb678abd10af22b83f.1620691329.git.osandov@fb.com Signed-off-by: Jens Axboe <axboe@kernel.dk>
5 files changed, 11 insertions, 10 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 0270cd7ca165..59b2499d3f8b 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2263,10 +2263,9 @@ static void bfq_remove_request(struct request_queue *q,
-static bool bfq_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio,
+static bool bfq_bio_merge(struct request_queue *q, struct bio *bio,
unsigned int nr_segs)
- struct request_queue *q = hctx->queue;
struct bfq_data *bfqd = q->elevator->elevator_data;
struct request *free = NULL;
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 42a365b1b9c0..996a4b2f73aa 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -358,14 +358,16 @@ bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio,
unsigned int nr_segs)
struct elevator_queue *e = q->elevator;
- struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
- struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
+ struct blk_mq_ctx *ctx;
+ struct blk_mq_hw_ctx *hctx;
bool ret = false;
enum hctx_type type;
if (e && e->type->ops.bio_merge)
- return e->type->ops.bio_merge(hctx, bio, nr_segs);
+ return e->type->ops.bio_merge(q, bio, nr_segs);
+ ctx = blk_mq_get_ctx(q);
+ hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
type = hctx->type;
if (!(hctx->flags & BLK_MQ_F_SHOULD_MERGE) ||
diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
index 8969e122f081..81e3279ecd57 100644
--- a/block/kyber-iosched.c
+++ b/block/kyber-iosched.c
@@ -561,11 +561,12 @@ static void kyber_limit_depth(unsigned int op, struct blk_mq_alloc_data *data)
-static bool kyber_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio,
+static bool kyber_bio_merge(struct request_queue *q, struct bio *bio,
unsigned int nr_segs)
+ struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
+ struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
struct kyber_hctx_data *khd = hctx->sched_data;
- struct blk_mq_ctx *ctx = blk_mq_get_ctx(hctx->queue);
struct kyber_ctx_queue *kcq = &khd->kcqs[ctx->index_hw[hctx->type]];
unsigned int sched_domain = kyber_sched_domain(bio->bi_opf);
struct list_head *rq_list = &kcq->rq_list[sched_domain];
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index 04aded71ead2..8eea2cbf2bf4 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -461,10 +461,9 @@ static int dd_request_merge(struct request_queue *q, struct request **rq,
-static bool dd_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio,
+static bool dd_bio_merge(struct request_queue *q, struct bio *bio,
unsigned int nr_segs)
- struct request_queue *q = hctx->queue;
struct deadline_data *dd = q->elevator->elevator_data;
struct request *free = NULL;
bool ret;
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index 1fe8e105b83b..dcb2f9022c1d 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -34,7 +34,7 @@ struct elevator_mq_ops {
void (*depth_updated)(struct blk_mq_hw_ctx *);
bool (*allow_merge)(struct request_queue *, struct request *, struct bio *);
- bool (*bio_merge)(struct blk_mq_hw_ctx *, struct bio *, unsigned int);
+ bool (*bio_merge)(struct request_queue *, struct bio *, unsigned int);
int (*request_merge)(struct request_queue *q, struct request **, struct bio *);
void (*request_merged)(struct request_queue *, struct request *, enum elv_merge);
void (*requests_merged)(struct request_queue *, struct request *, struct request *);

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