[PATCH 5.11 270/329] kyber: fix out of bounds access when preempted

From: Greg Kroah-Hartman
Date: Mon May 17 2021 - 11:50:02 EST

From: Omar Sandoval <osandov@xxxxxx>

[ Upstream commit efed9a3337e341bd0989161b97453b52567bc59d ]

__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@xxxxxxxxxx>
Signed-off-by: Omar Sandoval <osandov@xxxxxx>
Link: https://lore.kernel.org/r/c7598605401a48d5cfeadebb678abd10af22b83f.1620691329.git.osandov@xxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
block/bfq-iosched.c | 3 +--
block/blk-mq-sched.c | 8 +++++---
block/kyber-iosched.c | 5 +++--
block/mq-deadline.c | 3 +--
include/linux/elevator.h | 2 +-
5 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 5720978e4d09..c91dca641eb4 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2210,10 +2210,9 @@ 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 deff4e826e23..d93b45834776 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -348,14 +348,16 @@ 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) ||
list_empty_careful(&ctx->rq_lists[type]))
diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
index dc89199bc8c6..7f9ef773bf44 100644
--- a/block/kyber-iosched.c
+++ b/block/kyber-iosched.c
@@ -562,11 +562,12 @@ 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 800ac902809b..2b9635d0dcba 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,
return ELEVATOR_NO_MERGE;
}

-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 bacc40a0bdf3..bc26b4e11f62 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 *);
--
2.30.2