Re: [PATCH] target: Fix kref->refcount underflow in transport_cmd_finish_abort

["Nicholas A. Bellinger" <nab@linux-iscsi.org>]

(Adding Quinn CC')

Reviews please..?

On Sat, 2017-06-03 at 21:09 +0000, Nicholas A. Bellinger wrote:
> From: Nicholas Bellinger <nab@linux-iscsi.org>
> 
> This patch fixes a se_cmd->cmd_kref underflow during CMD_T_ABORTED
> when a fabric driver drops it's second reference from below the
> target_core_tmr.c based callers of transport_cmd_finish_abort().
> 
> Recently with the conversion of kref to refcount_t, this bug was
> manifesting itself as:
> 
> [705519.601034] refcount_t: underflow; use-after-free.
> [705519.604034] INFO: NMI handler (kgdb_nmi_handler) took too long to run: 20116.512 msecs
> [705539.719111] ------------[ cut here ]------------
> [705539.719117] WARNING: CPU: 3 PID: 26510 at lib/refcount.c:184 refcount_sub_and_test+0x33/0x51
> 
> Since the original kref atomic_t based kref_put() didn't check for
> underflow and only invoked the final callback when zero was reached,
> this bug did not manifest in practice since all se_cmd memory is
> using preallocated tags.
> 
> To address this, go ahead and propigate the existing return from
> transport_put_cmd() up via transport_cmd_finish_abort(), and
> change transport_cmd_finish_abort() + core_tmr_handle_tas_abort()
> callers to only do their local target_put_sess_cmd() if necessary.
> 
> Reported-by: Bart Van Assche <bart.vanassche@sandisk.com>
> Cc: Mike Christie <mchristi@redhat.com>
> Cc: Hannes Reinecke <hare@suse.de>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Himanshu Madhani <himanshu.madhani@qlogic.com>
> Cc: Sagi Grimberg <sagig@mellanox.com>
> Cc: stable@vger.kernel.org # 3.14+
> Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
> ---
>  drivers/target/target_core_internal.h  |  2 +-
>  drivers/target/target_core_tmr.c       | 16 ++++++++--------
>  drivers/target/target_core_transport.c |  9 ++++++---
>  3 files changed, 15 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/target/target_core_internal.h b/drivers/target/target_core_internal.h
> index 9ab7090..0912de7 100644
> --- a/drivers/target/target_core_internal.h
> +++ b/drivers/target/target_core_internal.h
> @@ -136,7 +136,7 @@ struct se_node_acl *core_tpg_add_initiator_node_acl(struct se_portal_group *tpg,
>  void	release_se_kmem_caches(void);
>  u32	scsi_get_new_index(scsi_index_t);
>  void	transport_subsystem_check_init(void);
> -void	transport_cmd_finish_abort(struct se_cmd *, int);
> +int	transport_cmd_finish_abort(struct se_cmd *, int);
>  unsigned char *transport_dump_cmd_direction(struct se_cmd *);
>  void	transport_dump_dev_state(struct se_device *, char *, int *);
>  void	transport_dump_dev_info(struct se_device *, struct se_lun *,
> diff --git a/drivers/target/target_core_tmr.c b/drivers/target/target_core_tmr.c
> index dce1e1b..13f47bf 100644
> --- a/drivers/target/target_core_tmr.c
> +++ b/drivers/target/target_core_tmr.c
> @@ -75,7 +75,7 @@ void core_tmr_release_req(struct se_tmr_req *tmr)
>  	kfree(tmr);
>  }
>  
> -static void core_tmr_handle_tas_abort(struct se_cmd *cmd, int tas)
> +static int core_tmr_handle_tas_abort(struct se_cmd *cmd, int tas)
>  {
>  	unsigned long flags;
>  	bool remove = true, send_tas;
> @@ -91,7 +91,7 @@ static void core_tmr_handle_tas_abort(struct se_cmd *cmd, int tas)
>  		transport_send_task_abort(cmd);
>  	}
>  
> -	transport_cmd_finish_abort(cmd, remove);
> +	return transport_cmd_finish_abort(cmd, remove);
>  }
>  
>  static int target_check_cdb_and_preempt(struct list_head *list,
> @@ -184,8 +184,8 @@ void core_tmr_abort_task(
>  		cancel_work_sync(&se_cmd->work);
>  		transport_wait_for_tasks(se_cmd);
>  
> -		transport_cmd_finish_abort(se_cmd, true);
> -		target_put_sess_cmd(se_cmd);
> +		if (!transport_cmd_finish_abort(se_cmd, true))
> +			target_put_sess_cmd(se_cmd);
>  
>  		printk("ABORT_TASK: Sending TMR_FUNCTION_COMPLETE for"
>  				" ref_tag: %llu\n", ref_tag);
> @@ -281,8 +281,8 @@ static void core_tmr_drain_tmr_list(
>  		cancel_work_sync(&cmd->work);
>  		transport_wait_for_tasks(cmd);
>  
> -		transport_cmd_finish_abort(cmd, 1);
> -		target_put_sess_cmd(cmd);
> +		if (!transport_cmd_finish_abort(cmd, 1))
> +			target_put_sess_cmd(cmd);
>  	}
>  }
>  
> @@ -380,8 +380,8 @@ static void core_tmr_drain_state_list(
>  		cancel_work_sync(&cmd->work);
>  		transport_wait_for_tasks(cmd);
>  
> -		core_tmr_handle_tas_abort(cmd, tas);
> -		target_put_sess_cmd(cmd);
> +		if (!core_tmr_handle_tas_abort(cmd, tas))
> +			target_put_sess_cmd(cmd);
>  	}
>  }
>  
> diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
> index 6025935..f1b3a46 100644
> --- a/drivers/target/target_core_transport.c
> +++ b/drivers/target/target_core_transport.c
> @@ -651,9 +651,10 @@ static void transport_lun_remove_cmd(struct se_cmd *cmd)
>  		percpu_ref_put(&lun->lun_ref);
>  }
>  
> -void transport_cmd_finish_abort(struct se_cmd *cmd, int remove)
> +int transport_cmd_finish_abort(struct se_cmd *cmd, int remove)
>  {
>  	bool ack_kref = (cmd->se_cmd_flags & SCF_ACK_KREF);
> +	int ret = 0;
>  
>  	if (cmd->se_cmd_flags & SCF_SE_LUN_CMD)
>  		transport_lun_remove_cmd(cmd);
> @@ -665,9 +666,11 @@ void transport_cmd_finish_abort(struct se_cmd *cmd, int remove)
>  		cmd->se_tfo->aborted_task(cmd);
>  
>  	if (transport_cmd_check_stop_to_fabric(cmd))
> -		return;
> +		return 1;
>  	if (remove && ack_kref)
> -		transport_put_cmd(cmd);
> +		ret = transport_put_cmd(cmd);
> +
> +	return ret;
>  }
>  
>  static void target_complete_failure_work(struct work_struct *work)