Re: [PATCH v4 4/4] scsi: core: Call blk_mq_free_tag_set() earlier

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On 12/07/2022 23:19, Bart Van Assche wrote:
There are two .exit_cmd_priv implementations. Both implementations use
resources associated with the SCSI host. Make sure that these resources are
still available when .exit_cmd_priv is called by moving the .exit_cmd_priv
calls from scsi_host_dev_release() to scsi_forget_host(). Moving
blk_mq_free_tag_set() from scsi_host_dev_release() to scsi_forget_host() is
safe because scsi_forget_host() waits until all SCSI devices associated

It seems to me that blk_mq_free_tag_set() is called from scsi_remove_host() now, right?

with the host have been removed.

This patch fixes the following use-after-free:

==================================================================
BUG: KASAN: use-after-free in srp_exit_cmd_priv+0x27/0xd0 [ib_srp]
Read of size 8 at addr ffff888100337000 by task multipathd/16727
Call Trace:
  <TASK>
  dump_stack_lvl+0x34/0x44
  print_report.cold+0x5e/0x5db
  kasan_report+0xab/0x120
  srp_exit_cmd_priv+0x27/0xd0 [ib_srp]
  scsi_mq_exit_request+0x4d/0x70
  blk_mq_free_rqs+0x143/0x410
  __blk_mq_free_map_and_rqs+0x6e/0x100
  blk_mq_free_tag_set+0x2b/0x160
  scsi_host_dev_release+0xf3/0x1a0
  device_release+0x54/0xe0
  kobject_put+0xa5/0x120
  device_release+0x54/0xe0
  kobject_put+0xa5/0x120
  scsi_device_dev_release_usercontext+0x4c1/0x4e0
  execute_in_process_context+0x23/0x90
  device_release+0x54/0xe0
  kobject_put+0xa5/0x120
  scsi_disk_release+0x3f/0x50
  device_release+0x54/0xe0
  kobject_put+0xa5/0x120
  disk_release+0x17f/0x1b0
  device_release+0x54/0xe0
  kobject_put+0xa5/0x120
  dm_put_table_device+0xa3/0x160 [dm_mod]
  dm_put_device+0xd0/0x140 [dm_mod]
  free_priority_group+0xd8/0x110 [dm_multipath]
  free_multipath+0x94/0xe0 [dm_multipath]
  dm_table_destroy+0xa2/0x1e0 [dm_mod]
  __dm_destroy+0x196/0x350 [dm_mod]
  dev_remove+0x10c/0x160 [dm_mod]
  ctl_ioctl+0x2c2/0x590 [dm_mod]
  dm_ctl_ioctl+0x5/0x10 [dm_mod]
  __x64_sys_ioctl+0xb4/0xf0
  dm_ctl_ioctl+0x5/0x10 [dm_mod]
  __x64_sys_ioctl+0xb4/0xf0
  do_syscall_64+0x3b/0x90
  entry_SYSCALL_64_after_hwframe+0x46/0xb0

Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Mike Christie <michael.christie@xxxxxxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxx>
Cc: John Garry <john.garry@xxxxxxxxxx>
Cc: Li Zhijian <lizhijian@xxxxxxxxxxx>
Reported-by: Li Zhijian <lizhijian@xxxxxxxxxxx>
Tested-by: Li Zhijian <lizhijian@xxxxxxxxxxx>
Fixes: 65ca846a5314 ("scsi: core: Introduce {init,exit}_cmd_priv()")
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
  drivers/scsi/hosts.c    | 10 +++++-----
  drivers/scsi/scsi_lib.c |  3 +++
  2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index 8fa98c8d0ee0..6c63672971f1 100644
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c
@@ -197,6 +197,8 @@ void scsi_remove_host(struct Scsi_Host *shost)
  	 * the dependent SCSI targets and devices are gone before returning.
  	 */
  	wait_event(shost->targets_wq, atomic_read(&shost->target_count) == 0);
+
+	scsi_mq_destroy_tags(shost);
  }
  EXPORT_SYMBOL(scsi_remove_host);
@@ -302,8 +304,8 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
  	return error;
/*
-	 * Any host allocation in this function will be freed in
-	 * scsi_host_dev_release().
+	 * Any resources associated with the SCSI host in this function except
+	 * the tag set will be freed by scsi_host_dev_release().
  	 */
   out_del_dev:
  	device_del(&shost->shost_dev);
@@ -319,6 +321,7 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
  	pm_runtime_disable(&shost->shost_gendev);
  	pm_runtime_set_suspended(&shost->shost_gendev);
  	pm_runtime_put_noidle(&shost->shost_gendev);
+	scsi_mq_destroy_tags(shost);
   fail:
  	return error;
  }
@@ -352,9 +355,6 @@ static void scsi_host_dev_release(struct device *dev)
  		kfree(dev_name(&shost->shost_dev));
  	}
- if (shost->tag_set.tags)
-		scsi_mq_destroy_tags(shost);
-
  	kfree(shost->shost_data);
ida_free(&host_index_ida, shost->host_no);
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 2aca0a838ca5..295c48fdb650 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1990,7 +1990,10 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
void scsi_mq_destroy_tags(struct Scsi_Host *shost)
  {
+	if (!shost->tag_set.tags)
+		return;
  	blk_mq_free_tag_set(&shost->tag_set);
+	WARN_ON_ONCE(shost->tag_set.tags);

blk_mq_free_tag_set() clears the tagset tags pointer, so I don't know why you don't trust the semantics of that API - this seems like paranoia.

  }
/**
.


Thanks,
john



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