[PATCH] blk-mq: don't free tags if the tag_set is used by other device in queue initialztion

Our test report a UAF on v5.10:

[ 1446.674930] ==================================================================
[ 1446.675970] BUG: KASAN: use-after-free in blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.676902] Read of size 8 at addr ffff8880185afd10 by task kworker/1:2/12348
[ 1446.677851]
[ 1446.678073] CPU: 1 PID: 12348 Comm: kworker/1:2 Not tainted 5.10.0-10177-gc9c81b1e346a #2
[ 1446.679168] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[ 1446.680692] Workqueue: kthrotld blk_throtl_dispatch_work_fn
[ 1446.681448] Call Trace:
[ 1446.681800]  dump_stack+0x9b/0xce
[ 1446.682259]  ? blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.682916]  print_address_description.constprop.6+0x3e/0x60
[ 1446.683688]  ? __cpuidle_text_end+0x5/0x5
[ 1446.684239]  ? vprintk_func+0x6b/0x120
[ 1446.684748]  ? blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.685373]  ? blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.685999]  kasan_report.cold.9+0x22/0x3a
[ 1446.686559]  ? blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.687186]  blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.687785]  blk_mq_dispatch_rq_list+0x21a/0x1d40
[ 1446.688427]  ? __sbitmap_get_word+0xc3/0xe0
[ 1446.688992]  ? blk_mq_dequeue_from_ctx+0x960/0x960
[ 1446.689641]  ? _raw_spin_lock+0x7a/0xd0
[ 1446.690164]  ? _raw_spin_lock_irq+0xd0/0xd0
[ 1446.690727]  ? sbitmap_get_shallow+0x3c9/0x4e0
[ 1446.691329]  ? sbitmap_any_bit_set+0x128/0x190
[ 1446.691928]  ? kyber_completed_request+0x290/0x290
[ 1446.692576]  __blk_mq_do_dispatch_sched+0x394/0x830
[ 1446.693237]  ? blk_mq_sched_request_inserted+0x100/0x100
[ 1446.693948]  ? __blk_queue_split+0x31d/0x1380
[ 1446.694540]  ? blk_integrity_merge_bio+0xc1/0x370
[ 1446.695182]  ? ll_back_merge_fn+0x694/0x1490
[ 1446.695758]  __blk_mq_sched_dispatch_requests+0x398/0x4f0
[ 1446.696484]  ? bio_attempt_back_merge+0x1cc/0x340
[ 1446.697121]  ? blk_mq_do_dispatch_ctx+0x570/0x570
[ 1446.697756]  ? _raw_spin_lock+0x7a/0xd0
[ 1446.698279]  blk_mq_sched_dispatch_requests+0xdf/0x140
[ 1446.698967]  __blk_mq_run_hw_queue+0xc0/0x270
[ 1446.699561]  __blk_mq_delay_run_hw_queue+0x4cc/0x550
[ 1446.700231]  ? kyber_has_work+0x9a/0x140
[ 1446.700760]  ? kyber_completed_request+0x290/0x290
[ 1446.701407]  blk_mq_run_hw_queue+0x13b/0x2b0
[ 1446.701982]  ? kyber_has_work+0x140/0x140
[ 1446.702593]  blk_mq_sched_insert_requests+0x1de/0x390
[ 1446.703309]  blk_mq_flush_plug_list+0x4b4/0x760
[ 1446.703946]  ? blk_mq_insert_requests+0x4b0/0x4b0
[ 1446.704644]  ? __bpf_trace_block_bio_complete+0x30/0x30
[ 1446.705408]  blk_flush_plug_list+0x2c5/0x480
[ 1446.706026]  ? blk_insert_cloned_request+0x460/0x460
[ 1446.706717]  ? _raw_spin_lock_irq+0x7b/0xd0
[ 1446.707292]  ? _raw_spin_lock_irqsave+0xe0/0xe0
[ 1446.707901]  ? set_next_entity+0x235/0x2210
[ 1446.708471]  blk_finish_plug+0x55/0xa0
[ 1446.708980]  blk_throtl_dispatch_work_fn+0x23b/0x2e0
[ 1446.709653]  ? tg_prfill_limit+0x8a0/0x8a0
[ 1446.710216]  ? read_word_at_a_time+0xe/0x20
[ 1446.710780]  ? strscpy+0x9a/0x320
[ 1446.711236]  process_one_work+0x6d4/0xfe0
[ 1446.711778]  worker_thread+0x91/0xc80
[ 1446.712281]  ? __kthread_parkme+0xb0/0x110
[ 1446.712834]  ? process_one_work+0xfe0/0xfe0
[ 1446.713400]  kthread+0x32d/0x3f0
[ 1446.713840]  ? kthread_park+0x170/0x170
[ 1446.714362]  ret_from_fork+0x1f/0x30
[ 1446.714846]
[ 1446.715062] Allocated by task 1:
[ 1446.715509]  kasan_save_stack+0x19/0x40
[ 1446.716026]  __kasan_kmalloc.constprop.1+0xc1/0xd0
[ 1446.716673]  blk_mq_init_tags+0x6d/0x330
[ 1446.717207]  blk_mq_alloc_rq_map+0x50/0x1c0
[ 1446.717769]  __blk_mq_alloc_map_and_request+0xe5/0x320
[ 1446.718459]  blk_mq_alloc_tag_set+0x679/0xdc0
[ 1446.719050]  scsi_add_host_with_dma.cold.3+0xa0/0x5db
[ 1446.719736]  virtscsi_probe+0x7bf/0xbd0
[ 1446.720265]  virtio_dev_probe+0x402/0x6c0
[ 1446.720808]  really_probe+0x276/0xde0
[ 1446.721320]  driver_probe_device+0x267/0x3d0
[ 1446.721892]  device_driver_attach+0xfe/0x140
[ 1446.722491]  __driver_attach+0x13a/0x2c0
[ 1446.723037]  bus_for_each_dev+0x146/0x1c0
[ 1446.723603]  bus_add_driver+0x3fc/0x680
[ 1446.724145]  driver_register+0x1c0/0x400
[ 1446.724693]  init+0xa2/0xe8
[ 1446.725091]  do_one_initcall+0x9e/0x310
[ 1446.725626]  kernel_init_freeable+0xc56/0xcb9
[ 1446.726231]  kernel_init+0x11/0x198
[ 1446.726714]  ret_from_fork+0x1f/0x30
[ 1446.727212]
[ 1446.727433] Freed by task 26992:
[ 1446.727882]  kasan_save_stack+0x19/0x40
[ 1446.728420]  kasan_set_track+0x1c/0x30
[ 1446.728943]  kasan_set_free_info+0x1b/0x30
[ 1446.729517]  __kasan_slab_free+0x111/0x160
[ 1446.730084]  kfree+0xb8/0x520
[ 1446.730507]  blk_mq_free_map_and_requests+0x10b/0x1b0
[ 1446.731206]  blk_mq_realloc_hw_ctxs+0x8cb/0x15b0
[ 1446.731844]  blk_mq_init_allocated_queue+0x374/0x1380
[ 1446.732540]  blk_mq_init_queue_data+0x7f/0xd0
[ 1446.733155]  scsi_mq_alloc_queue+0x45/0x170
[ 1446.733730]  scsi_alloc_sdev+0x73c/0xb20
[ 1446.734281]  scsi_probe_and_add_lun+0x9a6/0x2d90
[ 1446.734916]  __scsi_scan_target+0x208/0xc50
[ 1446.735500]  scsi_scan_channel.part.3+0x113/0x170
[ 1446.736149]  scsi_scan_host_selected+0x25a/0x360
[ 1446.736783]  store_scan+0x290/0x2d0
[ 1446.737275]  dev_attr_store+0x55/0x80
[ 1446.737782]  sysfs_kf_write+0x132/0x190
[ 1446.738313]  kernfs_fop_write_iter+0x319/0x4b0
[ 1446.738921]  new_sync_write+0x40e/0x5c0
[ 1446.739429]  vfs_write+0x519/0x720
[ 1446.739877]  ksys_write+0xf8/0x1f0
[ 1446.740332]  do_syscall_64+0x2d/0x40
[ 1446.740802]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 1446.741462]
[ 1446.741670] The buggy address belongs to the object at ffff8880185afd00
[ 1446.741670]  which belongs to the cache kmalloc-256 of size 256
[ 1446.743276] The buggy address is located 16 bytes inside of
[ 1446.743276]  256-byte region [ffff8880185afd00, ffff8880185afe00)
[ 1446.744765] The buggy address belongs to the page:
[ 1446.745416] page:ffffea0000616b00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x185ac
[ 1446.746694] head:ffffea0000616b00 order:2 compound_mapcount:0 compound_pincount:0
[ 1446.747719] flags: 0x1fffff80010200(slab|head)
[ 1446.748337] raw: 001fffff80010200 ffffea00006a3208 ffffea000061bf08 ffff88801004f240
[ 1446.749404] raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
[ 1446.750455] page dumped because: kasan: bad access detected
[ 1446.751227]
[ 1446.751445] Memory state around the buggy address:
[ 1446.752102]  ffff8880185afc00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 1446.753090]  ffff8880185afc80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 1446.754079] >ffff8880185afd00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 1446.755065]                          ^
[ 1446.755589]  ffff8880185afd80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 1446.756574]  ffff8880185afe00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 1446.757566] ==================================================================

Flag 'BLK_MQ_F_TAG_QUEUE_SHARED' will be set if the second device on the
same host initializes it's queue successfully. However, if the second
device failed to allocate memory in blk_mq_alloc_and_init_hctx() from
blk_mq_realloc_hw_ctxs() from blk_mq_init_allocated_queue(),
__blk_mq_free_map_and_rqs() will be called on error path, and if
'BLK_MQ_TAG_HCTX_SHARED' is not set, 'tag_set->tags' will be freed
while it's still used by the first device.

Fix the problem by checking if 'tag_set->tag_list' is emptly before
freeing 'tag_set->tag' during queue initialization.

Fixes: 868f2f0b7206 ("blk-mq: dynamic h/w context count")
Signed-off-by: Yu Kuai <redacted>
---
 block/blk-mq.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 3527ee251a85..529ad8c47377 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c

@@ -3571,7 +3571,7 @@ static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx(
 }
 
 static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
-						struct request_queue *q)
+				   struct request_queue *q)
 {
 	int i, j, end;
 	struct blk_mq_hw_ctx **hctxs = q->queue_hw_ctx;

@@ -3636,9 +3636,17 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
 
 	for (; j < end; j++) {
 		struct blk_mq_hw_ctx *hctx = hctxs[j];
+		bool free_tags = !blk_mq_is_shared_tags(set->flags) &&
+			!q->nr_hw_queues && list_empty(&set->tag_list);
 
 		if (hctx) {
-			__blk_mq_free_map_and_rqs(set, j);
+			/*
+			 * tags should not be freed if other device is using the
+			 * tagset. q->nr_hw_queues is zero means current
+			 * function is called from queue initialization.
+			 */
+			if (free_tags)
+				__blk_mq_free_map_and_rqs(set, j);
 			blk_mq_exit_hctx(q, set, hctx, j);
 			hctxs[j] = NULL;
 		}

-- 
2.31.1

On Sat, Nov 06, 2021 at 05:23:31PM +0800, Yu Kuai wrote:

__blk_mq_free_map_and_rqs() isn't supposed to call in
blk_mq_realloc_hw_ctxs(), so why can't we simply remove it here?


Thanks,
Ming

On 2021/11/8 9:31, Ming Lei wrote:

On Sat, Nov 06, 2021 at 05:23:31PM +0800, Yu Kuai wrote:

quoted

Our test report a UAF on v5.10:

[ 1446.674930] ==================================================================
[ 1446.675970] BUG: KASAN: use-after-free in blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.676902] Read of size 8 at addr ffff8880185afd10 by task kworker/1:2/12348
[ 1446.677851]
[ 1446.678073] CPU: 1 PID: 12348 Comm: kworker/1:2 Not tainted 5.10.0-10177-gc9c81b1e346a #2
[ 1446.679168] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[ 1446.680692] Workqueue: kthrotld blk_throtl_dispatch_work_fn
[ 1446.681448] Call Trace:
[ 1446.681800]  dump_stack+0x9b/0xce
[ 1446.682259]  ? blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.682916]  print_address_description.constprop.6+0x3e/0x60
[ 1446.683688]  ? __cpuidle_text_end+0x5/0x5
[ 1446.684239]  ? vprintk_func+0x6b/0x120
[ 1446.684748]  ? blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.685373]  ? blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.685999]  kasan_report.cold.9+0x22/0x3a
[ 1446.686559]  ? blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.687186]  blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.687785]  blk_mq_dispatch_rq_list+0x21a/0x1d40
[ 1446.688427]  ? __sbitmap_get_word+0xc3/0xe0
[ 1446.688992]  ? blk_mq_dequeue_from_ctx+0x960/0x960
[ 1446.689641]  ? _raw_spin_lock+0x7a/0xd0
[ 1446.690164]  ? _raw_spin_lock_irq+0xd0/0xd0
[ 1446.690727]  ? sbitmap_get_shallow+0x3c9/0x4e0
[ 1446.691329]  ? sbitmap_any_bit_set+0x128/0x190
[ 1446.691928]  ? kyber_completed_request+0x290/0x290
[ 1446.692576]  __blk_mq_do_dispatch_sched+0x394/0x830
[ 1446.693237]  ? blk_mq_sched_request_inserted+0x100/0x100
[ 1446.693948]  ? __blk_queue_split+0x31d/0x1380
[ 1446.694540]  ? blk_integrity_merge_bio+0xc1/0x370
[ 1446.695182]  ? ll_back_merge_fn+0x694/0x1490
[ 1446.695758]  __blk_mq_sched_dispatch_requests+0x398/0x4f0
[ 1446.696484]  ? bio_attempt_back_merge+0x1cc/0x340
[ 1446.697121]  ? blk_mq_do_dispatch_ctx+0x570/0x570
[ 1446.697756]  ? _raw_spin_lock+0x7a/0xd0
[ 1446.698279]  blk_mq_sched_dispatch_requests+0xdf/0x140
[ 1446.698967]  __blk_mq_run_hw_queue+0xc0/0x270
[ 1446.699561]  __blk_mq_delay_run_hw_queue+0x4cc/0x550
[ 1446.700231]  ? kyber_has_work+0x9a/0x140
[ 1446.700760]  ? kyber_completed_request+0x290/0x290
[ 1446.701407]  blk_mq_run_hw_queue+0x13b/0x2b0
[ 1446.701982]  ? kyber_has_work+0x140/0x140
[ 1446.702593]  blk_mq_sched_insert_requests+0x1de/0x390
[ 1446.703309]  blk_mq_flush_plug_list+0x4b4/0x760
[ 1446.703946]  ? blk_mq_insert_requests+0x4b0/0x4b0
[ 1446.704644]  ? __bpf_trace_block_bio_complete+0x30/0x30
[ 1446.705408]  blk_flush_plug_list+0x2c5/0x480
[ 1446.706026]  ? blk_insert_cloned_request+0x460/0x460
[ 1446.706717]  ? _raw_spin_lock_irq+0x7b/0xd0
[ 1446.707292]  ? _raw_spin_lock_irqsave+0xe0/0xe0
[ 1446.707901]  ? set_next_entity+0x235/0x2210
[ 1446.708471]  blk_finish_plug+0x55/0xa0
[ 1446.708980]  blk_throtl_dispatch_work_fn+0x23b/0x2e0
[ 1446.709653]  ? tg_prfill_limit+0x8a0/0x8a0
[ 1446.710216]  ? read_word_at_a_time+0xe/0x20
[ 1446.710780]  ? strscpy+0x9a/0x320
[ 1446.711236]  process_one_work+0x6d4/0xfe0
[ 1446.711778]  worker_thread+0x91/0xc80
[ 1446.712281]  ? __kthread_parkme+0xb0/0x110
[ 1446.712834]  ? process_one_work+0xfe0/0xfe0
[ 1446.713400]  kthread+0x32d/0x3f0
[ 1446.713840]  ? kthread_park+0x170/0x170
[ 1446.714362]  ret_from_fork+0x1f/0x30
[ 1446.714846]
[ 1446.715062] Allocated by task 1:
[ 1446.715509]  kasan_save_stack+0x19/0x40
[ 1446.716026]  __kasan_kmalloc.constprop.1+0xc1/0xd0
[ 1446.716673]  blk_mq_init_tags+0x6d/0x330
[ 1446.717207]  blk_mq_alloc_rq_map+0x50/0x1c0
[ 1446.717769]  __blk_mq_alloc_map_and_request+0xe5/0x320
[ 1446.718459]  blk_mq_alloc_tag_set+0x679/0xdc0
[ 1446.719050]  scsi_add_host_with_dma.cold.3+0xa0/0x5db
[ 1446.719736]  virtscsi_probe+0x7bf/0xbd0
[ 1446.720265]  virtio_dev_probe+0x402/0x6c0
[ 1446.720808]  really_probe+0x276/0xde0
[ 1446.721320]  driver_probe_device+0x267/0x3d0
[ 1446.721892]  device_driver_attach+0xfe/0x140
[ 1446.722491]  __driver_attach+0x13a/0x2c0
[ 1446.723037]  bus_for_each_dev+0x146/0x1c0
[ 1446.723603]  bus_add_driver+0x3fc/0x680
[ 1446.724145]  driver_register+0x1c0/0x400
[ 1446.724693]  init+0xa2/0xe8
[ 1446.725091]  do_one_initcall+0x9e/0x310
[ 1446.725626]  kernel_init_freeable+0xc56/0xcb9
[ 1446.726231]  kernel_init+0x11/0x198
[ 1446.726714]  ret_from_fork+0x1f/0x30
[ 1446.727212]
[ 1446.727433] Freed by task 26992:
[ 1446.727882]  kasan_save_stack+0x19/0x40
[ 1446.728420]  kasan_set_track+0x1c/0x30
[ 1446.728943]  kasan_set_free_info+0x1b/0x30
[ 1446.729517]  __kasan_slab_free+0x111/0x160
[ 1446.730084]  kfree+0xb8/0x520
[ 1446.730507]  blk_mq_free_map_and_requests+0x10b/0x1b0
[ 1446.731206]  blk_mq_realloc_hw_ctxs+0x8cb/0x15b0
[ 1446.731844]  blk_mq_init_allocated_queue+0x374/0x1380
[ 1446.732540]  blk_mq_init_queue_data+0x7f/0xd0
[ 1446.733155]  scsi_mq_alloc_queue+0x45/0x170
[ 1446.733730]  scsi_alloc_sdev+0x73c/0xb20
[ 1446.734281]  scsi_probe_and_add_lun+0x9a6/0x2d90
[ 1446.734916]  __scsi_scan_target+0x208/0xc50
[ 1446.735500]  scsi_scan_channel.part.3+0x113/0x170
[ 1446.736149]  scsi_scan_host_selected+0x25a/0x360
[ 1446.736783]  store_scan+0x290/0x2d0
[ 1446.737275]  dev_attr_store+0x55/0x80
[ 1446.737782]  sysfs_kf_write+0x132/0x190
[ 1446.738313]  kernfs_fop_write_iter+0x319/0x4b0
[ 1446.738921]  new_sync_write+0x40e/0x5c0
[ 1446.739429]  vfs_write+0x519/0x720
[ 1446.739877]  ksys_write+0xf8/0x1f0
[ 1446.740332]  do_syscall_64+0x2d/0x40
[ 1446.740802]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 1446.741462]
[ 1446.741670] The buggy address belongs to the object at ffff8880185afd00
[ 1446.741670]  which belongs to the cache kmalloc-256 of size 256
[ 1446.743276] The buggy address is located 16 bytes inside of
[ 1446.743276]  256-byte region [ffff8880185afd00, ffff8880185afe00)
[ 1446.744765] The buggy address belongs to the page:
[ 1446.745416] page:ffffea0000616b00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x185ac
[ 1446.746694] head:ffffea0000616b00 order:2 compound_mapcount:0 compound_pincount:0
[ 1446.747719] flags: 0x1fffff80010200(slab|head)
[ 1446.748337] raw: 001fffff80010200 ffffea00006a3208 ffffea000061bf08 ffff88801004f240
[ 1446.749404] raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
[ 1446.750455] page dumped because: kasan: bad access detected
[ 1446.751227]
[ 1446.751445] Memory state around the buggy address:
[ 1446.752102]  ffff8880185afc00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 1446.753090]  ffff8880185afc80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 1446.754079] >ffff8880185afd00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 1446.755065]                          ^
[ 1446.755589]  ffff8880185afd80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 1446.756574]  ffff8880185afe00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 1446.757566] ==================================================================

Flag 'BLK_MQ_F_TAG_QUEUE_SHARED' will be set if the second device on the
same host initializes it's queue successfully. However, if the second
device failed to allocate memory in blk_mq_alloc_and_init_hctx() from
blk_mq_realloc_hw_ctxs() from blk_mq_init_allocated_queue(),
__blk_mq_free_map_and_rqs() will be called on error path, and if
'BLK_MQ_TAG_HCTX_SHARED' is not set, 'tag_set->tags' will be freed
while it's still used by the first device.

Fix the problem by checking if 'tag_set->tag_list' is emptly before
freeing 'tag_set->tag' during queue initialization.

Fixes: 868f2f0b7206 ("blk-mq: dynamic h/w context count")
Signed-off-by: Yu Kuai <redacted>
---
  block/blk-mq.c | 12 ++++++++++--
  1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 3527ee251a85..529ad8c47377 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c

@@ -3571,7 +3571,7 @@ static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx(
  }
  
  static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
-						struct request_queue *q)
+				   struct request_queue *q)
  {
  	int i, j, end;
  	struct blk_mq_hw_ctx **hctxs = q->queue_hw_ctx;

@@ -3636,9 +3636,17 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
  
  	for (; j < end; j++) {
  		struct blk_mq_hw_ctx *hctx = hctxs[j];
+		bool free_tags = !blk_mq_is_shared_tags(set->flags) &&
+			!q->nr_hw_queues && list_empty(&set->tag_list);
  
  		if (hctx) {
-			__blk_mq_free_map_and_rqs(set, j);
+			/*
+			 * tags should not be freed if other device is using the
+			 * tagset. q->nr_hw_queues is zero means current
+			 * function is called from queue initialization.
+			 */
+			if (free_tags)
+				__blk_mq_free_map_and_rqs(set, j);
  			blk_mq_exit_hctx(q, set, hctx, j);
  			hctxs[j] = NULL;

__blk_mq_free_map_and_rqs() isn't supposed to call in
blk_mq_realloc_hw_ctxs(), so why can't we simply remove it here?

__blk_mq_update_nr_hw_queues
     blk_mq_realloc_hw_ctxs
         if (q->nr_hw_queues != set->nr_hw_queues)
             set->nr_hw_queues = prev_nr_hw_queues;
If 'tag_set' expansion failed, 'set->nr_hw_queues' will fallback 
previous  value. So If we don't
call '__blk_mq_free_map_and_rqs' to release the newly allocated hardware 
context will lead to
memory leak.

Thanks,
Ming

.

On Mon, Nov 08, 2021 at 10:08:52AM +0800, yebin wrote:

On 2021/11/8 9:31, Ming Lei wrote:

quoted

On Sat, Nov 06, 2021 at 05:23:31PM +0800, Yu Kuai wrote:

quoted

Our test report a UAF on v5.10:

[ 1446.674930] ==================================================================
[ 1446.675970] BUG: KASAN: use-after-free in blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.676902] Read of size 8 at addr ffff8880185afd10 by task kworker/1:2/12348
[ 1446.677851]
[ 1446.678073] CPU: 1 PID: 12348 Comm: kworker/1:2 Not tainted 5.10.0-10177-gc9c81b1e346a #2
[ 1446.679168] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[ 1446.680692] Workqueue: kthrotld blk_throtl_dispatch_work_fn
[ 1446.681448] Call Trace:
[ 1446.681800]  dump_stack+0x9b/0xce
[ 1446.682259]  ? blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.682916]  print_address_description.constprop.6+0x3e/0x60
[ 1446.683688]  ? __cpuidle_text_end+0x5/0x5
[ 1446.684239]  ? vprintk_func+0x6b/0x120
[ 1446.684748]  ? blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.685373]  ? blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.685999]  kasan_report.cold.9+0x22/0x3a
[ 1446.686559]  ? blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.687186]  blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.687785]  blk_mq_dispatch_rq_list+0x21a/0x1d40
[ 1446.688427]  ? __sbitmap_get_word+0xc3/0xe0
[ 1446.688992]  ? blk_mq_dequeue_from_ctx+0x960/0x960
[ 1446.689641]  ? _raw_spin_lock+0x7a/0xd0
[ 1446.690164]  ? _raw_spin_lock_irq+0xd0/0xd0
[ 1446.690727]  ? sbitmap_get_shallow+0x3c9/0x4e0
[ 1446.691329]  ? sbitmap_any_bit_set+0x128/0x190
[ 1446.691928]  ? kyber_completed_request+0x290/0x290
[ 1446.692576]  __blk_mq_do_dispatch_sched+0x394/0x830
[ 1446.693237]  ? blk_mq_sched_request_inserted+0x100/0x100
[ 1446.693948]  ? __blk_queue_split+0x31d/0x1380
[ 1446.694540]  ? blk_integrity_merge_bio+0xc1/0x370
[ 1446.695182]  ? ll_back_merge_fn+0x694/0x1490
[ 1446.695758]  __blk_mq_sched_dispatch_requests+0x398/0x4f0
[ 1446.696484]  ? bio_attempt_back_merge+0x1cc/0x340
[ 1446.697121]  ? blk_mq_do_dispatch_ctx+0x570/0x570
[ 1446.697756]  ? _raw_spin_lock+0x7a/0xd0
[ 1446.698279]  blk_mq_sched_dispatch_requests+0xdf/0x140
[ 1446.698967]  __blk_mq_run_hw_queue+0xc0/0x270
[ 1446.699561]  __blk_mq_delay_run_hw_queue+0x4cc/0x550
[ 1446.700231]  ? kyber_has_work+0x9a/0x140
[ 1446.700760]  ? kyber_completed_request+0x290/0x290
[ 1446.701407]  blk_mq_run_hw_queue+0x13b/0x2b0
[ 1446.701982]  ? kyber_has_work+0x140/0x140
[ 1446.702593]  blk_mq_sched_insert_requests+0x1de/0x390
[ 1446.703309]  blk_mq_flush_plug_list+0x4b4/0x760
[ 1446.703946]  ? blk_mq_insert_requests+0x4b0/0x4b0
[ 1446.704644]  ? __bpf_trace_block_bio_complete+0x30/0x30
[ 1446.705408]  blk_flush_plug_list+0x2c5/0x480
[ 1446.706026]  ? blk_insert_cloned_request+0x460/0x460
[ 1446.706717]  ? _raw_spin_lock_irq+0x7b/0xd0
[ 1446.707292]  ? _raw_spin_lock_irqsave+0xe0/0xe0
[ 1446.707901]  ? set_next_entity+0x235/0x2210
[ 1446.708471]  blk_finish_plug+0x55/0xa0
[ 1446.708980]  blk_throtl_dispatch_work_fn+0x23b/0x2e0
[ 1446.709653]  ? tg_prfill_limit+0x8a0/0x8a0
[ 1446.710216]  ? read_word_at_a_time+0xe/0x20
[ 1446.710780]  ? strscpy+0x9a/0x320
[ 1446.711236]  process_one_work+0x6d4/0xfe0
[ 1446.711778]  worker_thread+0x91/0xc80
[ 1446.712281]  ? __kthread_parkme+0xb0/0x110
[ 1446.712834]  ? process_one_work+0xfe0/0xfe0
[ 1446.713400]  kthread+0x32d/0x3f0
[ 1446.713840]  ? kthread_park+0x170/0x170
[ 1446.714362]  ret_from_fork+0x1f/0x30
[ 1446.714846]
[ 1446.715062] Allocated by task 1:
[ 1446.715509]  kasan_save_stack+0x19/0x40
[ 1446.716026]  __kasan_kmalloc.constprop.1+0xc1/0xd0
[ 1446.716673]  blk_mq_init_tags+0x6d/0x330
[ 1446.717207]  blk_mq_alloc_rq_map+0x50/0x1c0
[ 1446.717769]  __blk_mq_alloc_map_and_request+0xe5/0x320
[ 1446.718459]  blk_mq_alloc_tag_set+0x679/0xdc0
[ 1446.719050]  scsi_add_host_with_dma.cold.3+0xa0/0x5db
[ 1446.719736]  virtscsi_probe+0x7bf/0xbd0
[ 1446.720265]  virtio_dev_probe+0x402/0x6c0
[ 1446.720808]  really_probe+0x276/0xde0
[ 1446.721320]  driver_probe_device+0x267/0x3d0
[ 1446.721892]  device_driver_attach+0xfe/0x140
[ 1446.722491]  __driver_attach+0x13a/0x2c0
[ 1446.723037]  bus_for_each_dev+0x146/0x1c0
[ 1446.723603]  bus_add_driver+0x3fc/0x680
[ 1446.724145]  driver_register+0x1c0/0x400
[ 1446.724693]  init+0xa2/0xe8
[ 1446.725091]  do_one_initcall+0x9e/0x310
[ 1446.725626]  kernel_init_freeable+0xc56/0xcb9
[ 1446.726231]  kernel_init+0x11/0x198
[ 1446.726714]  ret_from_fork+0x1f/0x30
[ 1446.727212]
[ 1446.727433] Freed by task 26992:
[ 1446.727882]  kasan_save_stack+0x19/0x40
[ 1446.728420]  kasan_set_track+0x1c/0x30
[ 1446.728943]  kasan_set_free_info+0x1b/0x30
[ 1446.729517]  __kasan_slab_free+0x111/0x160
[ 1446.730084]  kfree+0xb8/0x520
[ 1446.730507]  blk_mq_free_map_and_requests+0x10b/0x1b0
[ 1446.731206]  blk_mq_realloc_hw_ctxs+0x8cb/0x15b0
[ 1446.731844]  blk_mq_init_allocated_queue+0x374/0x1380
[ 1446.732540]  blk_mq_init_queue_data+0x7f/0xd0
[ 1446.733155]  scsi_mq_alloc_queue+0x45/0x170
[ 1446.733730]  scsi_alloc_sdev+0x73c/0xb20
[ 1446.734281]  scsi_probe_and_add_lun+0x9a6/0x2d90
[ 1446.734916]  __scsi_scan_target+0x208/0xc50
[ 1446.735500]  scsi_scan_channel.part.3+0x113/0x170
[ 1446.736149]  scsi_scan_host_selected+0x25a/0x360
[ 1446.736783]  store_scan+0x290/0x2d0
[ 1446.737275]  dev_attr_store+0x55/0x80
[ 1446.737782]  sysfs_kf_write+0x132/0x190
[ 1446.738313]  kernfs_fop_write_iter+0x319/0x4b0
[ 1446.738921]  new_sync_write+0x40e/0x5c0
[ 1446.739429]  vfs_write+0x519/0x720
[ 1446.739877]  ksys_write+0xf8/0x1f0
[ 1446.740332]  do_syscall_64+0x2d/0x40
[ 1446.740802]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 1446.741462]
[ 1446.741670] The buggy address belongs to the object at ffff8880185afd00
[ 1446.741670]  which belongs to the cache kmalloc-256 of size 256
[ 1446.743276] The buggy address is located 16 bytes inside of
[ 1446.743276]  256-byte region [ffff8880185afd00, ffff8880185afe00)
[ 1446.744765] The buggy address belongs to the page:
[ 1446.745416] page:ffffea0000616b00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x185ac
[ 1446.746694] head:ffffea0000616b00 order:2 compound_mapcount:0 compound_pincount:0
[ 1446.747719] flags: 0x1fffff80010200(slab|head)
[ 1446.748337] raw: 001fffff80010200 ffffea00006a3208 ffffea000061bf08 ffff88801004f240
[ 1446.749404] raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
[ 1446.750455] page dumped because: kasan: bad access detected
[ 1446.751227]
[ 1446.751445] Memory state around the buggy address:
[ 1446.752102]  ffff8880185afc00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 1446.753090]  ffff8880185afc80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 1446.754079] >ffff8880185afd00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 1446.755065]                          ^
[ 1446.755589]  ffff8880185afd80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 1446.756574]  ffff8880185afe00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 1446.757566] ==================================================================

Flag 'BLK_MQ_F_TAG_QUEUE_SHARED' will be set if the second device on the
same host initializes it's queue successfully. However, if the second
device failed to allocate memory in blk_mq_alloc_and_init_hctx() from
blk_mq_realloc_hw_ctxs() from blk_mq_init_allocated_queue(),
__blk_mq_free_map_and_rqs() will be called on error path, and if
'BLK_MQ_TAG_HCTX_SHARED' is not set, 'tag_set->tags' will be freed
while it's still used by the first device.

Fix the problem by checking if 'tag_set->tag_list' is emptly before
freeing 'tag_set->tag' during queue initialization.

Fixes: 868f2f0b7206 ("blk-mq: dynamic h/w context count")
Signed-off-by: Yu Kuai <redacted>
---
  block/blk-mq.c | 12 ++++++++++--
  1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 3527ee251a85..529ad8c47377 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c

@@ -3571,7 +3571,7 @@ static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx(
  }
  static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
-						struct request_queue *q)
+				   struct request_queue *q)
  {
  	int i, j, end;
  	struct blk_mq_hw_ctx **hctxs = q->queue_hw_ctx;

@@ -3636,9 +3636,17 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
  	for (; j < end; j++) {
  		struct blk_mq_hw_ctx *hctx = hctxs[j];
+		bool free_tags = !blk_mq_is_shared_tags(set->flags) &&
+			!q->nr_hw_queues && list_empty(&set->tag_list);
  		if (hctx) {
-			__blk_mq_free_map_and_rqs(set, j);
+			/*
+			 * tags should not be freed if other device is using the
+			 * tagset. q->nr_hw_queues is zero means current
+			 * function is called from queue initialization.
+			 */
+			if (free_tags)
+				__blk_mq_free_map_and_rqs(set, j);
  			blk_mq_exit_hctx(q, set, hctx, j);
  			hctxs[j] = NULL;

__blk_mq_free_map_and_rqs() isn't supposed to call in
blk_mq_realloc_hw_ctxs(), so why can't we simply remove it here?

__blk_mq_update_nr_hw_queues
    blk_mq_realloc_hw_ctxs
        if (q->nr_hw_queues != set->nr_hw_queues)
            set->nr_hw_queues = prev_nr_hw_queues;
If 'tag_set' expansion failed, 'set->nr_hw_queues' will fallback previous
value. So If we don't
call '__blk_mq_free_map_and_rqs' to release the newly allocated hardware
context will lead to
memory leak.

Then the correct way is to move the freeing of extra map_and_tags into
__blk_mq_update_nr_hw_queues() where it is safe and supposed to do such
thing.


Thanks,
Ming

On 2021/11/8 10:16, Ming Lei wrote:

On Mon, Nov 08, 2021 at 10:08:52AM +0800, yebin wrote:

quoted

On 2021/11/8 9:31, Ming Lei wrote:

quoted

On Sat, Nov 06, 2021 at 05:23:31PM +0800, Yu Kuai wrote:

quoted

Our test report a UAF on v5.10:

[ 1446.674930] ==================================================================
[ 1446.675970] BUG: KASAN: use-after-free in blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.676902] Read of size 8 at addr ffff8880185afd10 by task kworker/1:2/12348
[ 1446.677851]
[ 1446.678073] CPU: 1 PID: 12348 Comm: kworker/1:2 Not tainted 5.10.0-10177-gc9c81b1e346a #2
[ 1446.679168] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[ 1446.680692] Workqueue: kthrotld blk_throtl_dispatch_work_fn
[ 1446.681448] Call Trace:
[ 1446.681800]  dump_stack+0x9b/0xce
[ 1446.682259]  ? blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.682916]  print_address_description.constprop.6+0x3e/0x60
[ 1446.683688]  ? __cpuidle_text_end+0x5/0x5
[ 1446.684239]  ? vprintk_func+0x6b/0x120
[ 1446.684748]  ? blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.685373]  ? blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.685999]  kasan_report.cold.9+0x22/0x3a
[ 1446.686559]  ? blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.687186]  blk_mq_get_driver_tag+0x9a4/0xa90
[ 1446.687785]  blk_mq_dispatch_rq_list+0x21a/0x1d40
[ 1446.688427]  ? __sbitmap_get_word+0xc3/0xe0
[ 1446.688992]  ? blk_mq_dequeue_from_ctx+0x960/0x960
[ 1446.689641]  ? _raw_spin_lock+0x7a/0xd0
[ 1446.690164]  ? _raw_spin_lock_irq+0xd0/0xd0
[ 1446.690727]  ? sbitmap_get_shallow+0x3c9/0x4e0
[ 1446.691329]  ? sbitmap_any_bit_set+0x128/0x190
[ 1446.691928]  ? kyber_completed_request+0x290/0x290
[ 1446.692576]  __blk_mq_do_dispatch_sched+0x394/0x830
[ 1446.693237]  ? blk_mq_sched_request_inserted+0x100/0x100
[ 1446.693948]  ? __blk_queue_split+0x31d/0x1380
[ 1446.694540]  ? blk_integrity_merge_bio+0xc1/0x370
[ 1446.695182]  ? ll_back_merge_fn+0x694/0x1490
[ 1446.695758]  __blk_mq_sched_dispatch_requests+0x398/0x4f0
[ 1446.696484]  ? bio_attempt_back_merge+0x1cc/0x340
[ 1446.697121]  ? blk_mq_do_dispatch_ctx+0x570/0x570
[ 1446.697756]  ? _raw_spin_lock+0x7a/0xd0
[ 1446.698279]  blk_mq_sched_dispatch_requests+0xdf/0x140
[ 1446.698967]  __blk_mq_run_hw_queue+0xc0/0x270
[ 1446.699561]  __blk_mq_delay_run_hw_queue+0x4cc/0x550
[ 1446.700231]  ? kyber_has_work+0x9a/0x140
[ 1446.700760]  ? kyber_completed_request+0x290/0x290
[ 1446.701407]  blk_mq_run_hw_queue+0x13b/0x2b0
[ 1446.701982]  ? kyber_has_work+0x140/0x140
[ 1446.702593]  blk_mq_sched_insert_requests+0x1de/0x390
[ 1446.703309]  blk_mq_flush_plug_list+0x4b4/0x760
[ 1446.703946]  ? blk_mq_insert_requests+0x4b0/0x4b0
[ 1446.704644]  ? __bpf_trace_block_bio_complete+0x30/0x30
[ 1446.705408]  blk_flush_plug_list+0x2c5/0x480
[ 1446.706026]  ? blk_insert_cloned_request+0x460/0x460
[ 1446.706717]  ? _raw_spin_lock_irq+0x7b/0xd0
[ 1446.707292]  ? _raw_spin_lock_irqsave+0xe0/0xe0
[ 1446.707901]  ? set_next_entity+0x235/0x2210
[ 1446.708471]  blk_finish_plug+0x55/0xa0
[ 1446.708980]  blk_throtl_dispatch_work_fn+0x23b/0x2e0
[ 1446.709653]  ? tg_prfill_limit+0x8a0/0x8a0
[ 1446.710216]  ? read_word_at_a_time+0xe/0x20
[ 1446.710780]  ? strscpy+0x9a/0x320
[ 1446.711236]  process_one_work+0x6d4/0xfe0
[ 1446.711778]  worker_thread+0x91/0xc80
[ 1446.712281]  ? __kthread_parkme+0xb0/0x110
[ 1446.712834]  ? process_one_work+0xfe0/0xfe0
[ 1446.713400]  kthread+0x32d/0x3f0
[ 1446.713840]  ? kthread_park+0x170/0x170
[ 1446.714362]  ret_from_fork+0x1f/0x30
[ 1446.714846]
[ 1446.715062] Allocated by task 1:
[ 1446.715509]  kasan_save_stack+0x19/0x40
[ 1446.716026]  __kasan_kmalloc.constprop.1+0xc1/0xd0
[ 1446.716673]  blk_mq_init_tags+0x6d/0x330
[ 1446.717207]  blk_mq_alloc_rq_map+0x50/0x1c0
[ 1446.717769]  __blk_mq_alloc_map_and_request+0xe5/0x320
[ 1446.718459]  blk_mq_alloc_tag_set+0x679/0xdc0
[ 1446.719050]  scsi_add_host_with_dma.cold.3+0xa0/0x5db
[ 1446.719736]  virtscsi_probe+0x7bf/0xbd0
[ 1446.720265]  virtio_dev_probe+0x402/0x6c0
[ 1446.720808]  really_probe+0x276/0xde0
[ 1446.721320]  driver_probe_device+0x267/0x3d0
[ 1446.721892]  device_driver_attach+0xfe/0x140
[ 1446.722491]  __driver_attach+0x13a/0x2c0
[ 1446.723037]  bus_for_each_dev+0x146/0x1c0
[ 1446.723603]  bus_add_driver+0x3fc/0x680
[ 1446.724145]  driver_register+0x1c0/0x400
[ 1446.724693]  init+0xa2/0xe8
[ 1446.725091]  do_one_initcall+0x9e/0x310
[ 1446.725626]  kernel_init_freeable+0xc56/0xcb9
[ 1446.726231]  kernel_init+0x11/0x198
[ 1446.726714]  ret_from_fork+0x1f/0x30
[ 1446.727212]
[ 1446.727433] Freed by task 26992:
[ 1446.727882]  kasan_save_stack+0x19/0x40
[ 1446.728420]  kasan_set_track+0x1c/0x30
[ 1446.728943]  kasan_set_free_info+0x1b/0x30
[ 1446.729517]  __kasan_slab_free+0x111/0x160
[ 1446.730084]  kfree+0xb8/0x520
[ 1446.730507]  blk_mq_free_map_and_requests+0x10b/0x1b0
[ 1446.731206]  blk_mq_realloc_hw_ctxs+0x8cb/0x15b0
[ 1446.731844]  blk_mq_init_allocated_queue+0x374/0x1380
[ 1446.732540]  blk_mq_init_queue_data+0x7f/0xd0
[ 1446.733155]  scsi_mq_alloc_queue+0x45/0x170
[ 1446.733730]  scsi_alloc_sdev+0x73c/0xb20
[ 1446.734281]  scsi_probe_and_add_lun+0x9a6/0x2d90
[ 1446.734916]  __scsi_scan_target+0x208/0xc50
[ 1446.735500]  scsi_scan_channel.part.3+0x113/0x170
[ 1446.736149]  scsi_scan_host_selected+0x25a/0x360
[ 1446.736783]  store_scan+0x290/0x2d0
[ 1446.737275]  dev_attr_store+0x55/0x80
[ 1446.737782]  sysfs_kf_write+0x132/0x190
[ 1446.738313]  kernfs_fop_write_iter+0x319/0x4b0
[ 1446.738921]  new_sync_write+0x40e/0x5c0
[ 1446.739429]  vfs_write+0x519/0x720
[ 1446.739877]  ksys_write+0xf8/0x1f0
[ 1446.740332]  do_syscall_64+0x2d/0x40
[ 1446.740802]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 1446.741462]
[ 1446.741670] The buggy address belongs to the object at ffff8880185afd00
[ 1446.741670]  which belongs to the cache kmalloc-256 of size 256
[ 1446.743276] The buggy address is located 16 bytes inside of
[ 1446.743276]  256-byte region [ffff8880185afd00, ffff8880185afe00)
[ 1446.744765] The buggy address belongs to the page:
[ 1446.745416] page:ffffea0000616b00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x185ac
[ 1446.746694] head:ffffea0000616b00 order:2 compound_mapcount:0 compound_pincount:0
[ 1446.747719] flags: 0x1fffff80010200(slab|head)
[ 1446.748337] raw: 001fffff80010200 ffffea00006a3208 ffffea000061bf08 ffff88801004f240
[ 1446.749404] raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
[ 1446.750455] page dumped because: kasan: bad access detected
[ 1446.751227]
[ 1446.751445] Memory state around the buggy address:
[ 1446.752102]  ffff8880185afc00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 1446.753090]  ffff8880185afc80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 1446.754079] >ffff8880185afd00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 1446.755065]                          ^
[ 1446.755589]  ffff8880185afd80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 1446.756574]  ffff8880185afe00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 1446.757566] ==================================================================

Flag 'BLK_MQ_F_TAG_QUEUE_SHARED' will be set if the second device on the
same host initializes it's queue successfully. However, if the second
device failed to allocate memory in blk_mq_alloc_and_init_hctx() from
blk_mq_realloc_hw_ctxs() from blk_mq_init_allocated_queue(),
__blk_mq_free_map_and_rqs() will be called on error path, and if
'BLK_MQ_TAG_HCTX_SHARED' is not set, 'tag_set->tags' will be freed
while it's still used by the first device.

Fix the problem by checking if 'tag_set->tag_list' is emptly before
freeing 'tag_set->tag' during queue initialization.

Fixes: 868f2f0b7206 ("blk-mq: dynamic h/w context count")
Signed-off-by: Yu Kuai <redacted>
---
   block/blk-mq.c | 12 ++++++++++--
   1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 3527ee251a85..529ad8c47377 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c

@@ -3571,7 +3571,7 @@ static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx(
   }
   static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
-						struct request_queue *q)
+				   struct request_queue *q)
   {
   	int i, j, end;
   	struct blk_mq_hw_ctx **hctxs = q->queue_hw_ctx;

@@ -3636,9 +3636,17 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
   	for (; j < end; j++) {
   		struct blk_mq_hw_ctx *hctx = hctxs[j];
+		bool free_tags = !blk_mq_is_shared_tags(set->flags) &&
+			!q->nr_hw_queues && list_empty(&set->tag_list);
   		if (hctx) {
-			__blk_mq_free_map_and_rqs(set, j);
+			/*
+			 * tags should not be freed if other device is using the
+			 * tagset. q->nr_hw_queues is zero means current
+			 * function is called from queue initialization.
+			 */
+			if (free_tags)
+				__blk_mq_free_map_and_rqs(set, j);
   			blk_mq_exit_hctx(q, set, hctx, j);
   			hctxs[j] = NULL;

__blk_mq_free_map_and_rqs() isn't supposed to call in
blk_mq_realloc_hw_ctxs(), so why can't we simply remove it here?

__blk_mq_update_nr_hw_queues
     blk_mq_realloc_hw_ctxs
         if (q->nr_hw_queues != set->nr_hw_queues)
             set->nr_hw_queues = prev_nr_hw_queues;
If 'tag_set' expansion failed, 'set->nr_hw_queues' will fallback previous
value. So If we don't
call '__blk_mq_free_map_and_rqs' to release the newly allocated hardware
context will lead to
memory leak.

Then the correct way is to move the freeing of extra map_and_tags into
__blk_mq_update_nr_hw_queues() where it is safe and supposed to do such
thing.


Thanks,
Ming

.

Good idea, i will send V2 according to your  suggestion.
(Yu Kuai entrusted me to deal with this issue.)