[PATCH 2/2] xen/scsiback: free the command tag on the TMR submit-failure path

[Michael Bommarito <michael.bommarito@gmail.com>]

scsiback_device_action() obtains a command tag in
scsiback_get_pend_req() and submits a task-management request with
target_submit_tmr(). When target_submit_tmr() fails it returns < 0
and scsiback jumps to the err: label, which sends a response but
frees nothing, leaking the tag.

Impact: a pvSCSI guest can leak the command tags of a LUN's
session, stopping the LUN, by issuing VSCSIIF_ACT_SCSI_ABORT or
RESET requests whenever target_submit_tmr() fails.

transport_generic_free_cmd() cannot be used here. By the time
target_submit_tmr() returns an error it has already run
__target_init_cmd() (so se_cmd->cmd_kref is one, not zero), and on
its target_get_sess_cmd() error path it has freed se_cmd->se_tmr_req
via core_tmr_release_req() while leaving SCF_SCSI_TMR_CDB set and
the pointer dangling. Letting the command release run
target_free_cmd_mem() would then double-free se_tmr_req.

Use the same helper, which returns just the tag, on this path too.

Fixes: 2dbcdf33dbf6 ("xen-scsiback: Convert to percpu_ida tag allocation")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
---
 drivers/xen/xen-scsiback.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/xen/xen-scsiback.c b/drivers/xen/xen-scsiback.c
index f324732eba7f8..c7036e0e41bda 100644
--- a/drivers/xen/xen-scsiback.c
+++ b/drivers/xen/xen-scsiback.c
@@ -658,7 +658,7 @@ static void scsiback_device_action(struct vscsibk_pend *pending_req,
 	return;
 
 err:
-	scsiback_do_resp_with_sense(NULL, err, 0, pending_req);
+	scsiback_resp_and_free(pending_req, err);
 }
 
 /*
-- 
2.53.0