Re: [PATCH] scsi: target: fix NULL dereference on XCOPY completion

[michael.christie@oracle.com]

On 7/20/21 5:55 PM, David Disseldorp wrote:
> CPU affinity control added with 39ae3edda325 makes target_complete_cmd()
> queue work on a CPU based on se_tpg->se_tpg_wwn->cmd_compl_affinity
> state.
> 
> LIO's EXTENDED COPY worker is a special case in that read/write cmds
> are dispatched using the global xcopy_pt_tpg, which carries a NULL
> se_tpg_wwn pointer following initialization in target_xcopy_setup_pt().
> 
> The NULL xcopy_pt_tpg->se_tpg_wwn pointer is dereferenced on completion
> of any EXTENDED COPY initiated read/write cmds. E.g using the libiscsi
> SCSI.ExtendedCopy.Simple test:
>   BUG: kernel NULL pointer dereference, address: 00000000000001a8
>   RIP: 0010:target_complete_cmd+0x9d/0x130 [target_core_mod]
>   Call Trace:
>    fd_execute_rw+0x148/0x42a [target_core_file]
>    ? __dynamic_pr_debug+0xa7/0xe0
>    ? target_check_reservation+0x5b/0x940 [target_core_mod]
>    __target_execute_cmd+0x1e/0x90 [target_core_mod]
>    transport_generic_new_cmd+0x17c/0x330 [target_core_mod]
>    target_xcopy_issue_pt_cmd+0x9/0x60 [target_core_mod]
>    target_xcopy_read_source.isra.7+0x10b/0x1b0 [target_core_mod]
>    ? target_check_fua+0x40/0x40 [target_core_mod]
>    ? transport_complete_task_attr+0x130/0x130 [target_core_mod]
>    target_xcopy_do_work+0x61f/0xc00 [target_core_mod]
> 
> This fix makes target_complete_cmd() queue work on se_cmd->cpuid if
> se_tpg_wwn is NULL.
> 
> Fixes: 39ae3edda325 ("scsi: target: core: Make completion affinity configurable")
> Signed-off-by: David Disseldorp <ddiss@suse.de>
> Cc: Lee Duncan <lduncan@suse.com>
> Cc: Mike Christie <michael.christie@oracle.com>
> ---
>  drivers/target/target_core_transport.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
> index 7e35eddd9eb7..26ceabe34de5 100644
> --- a/drivers/target/target_core_transport.c
> +++ b/drivers/target/target_core_transport.c
> @@ -886,7 +886,7 @@ void target_complete_cmd(struct se_cmd *cmd, u8 scsi_status)
>  	INIT_WORK(&cmd->work, success ? target_complete_ok_work :
>  		  target_complete_failure_work);
>  
> -	if (wwn->cmd_compl_affinity == SE_COMPL_AFFINITY_CPUID)
> +	if (!wwn || wwn->cmd_compl_affinity == SE_COMPL_AFFINITY_CPUID)
>  		cpu = cmd->cpuid;
>  	else
>  		cpu = wwn->cmd_compl_affinity;
> 

Reviewed-by: Mike Christie <michael.christie@oracle.com>