[PATCH V2 4/4] pm80xx: make pm8001_mpi_set_nvmd_resp free of race condition

[Viswas G <Viswas.G@microchip.com.com>]

From: yuuzheng <yuuzheng@google.com>

The use-after-free or null-pointer error occurs when the 251-byte
response data are copied from IOMB buffer to response message
buffer in function mp8001_mpi_set_nvmd_resp. pm8001_mpi_set_nvmd_resp
is a function to process the response of command set_nvmd_data_resp.
After sending the command set_nvmd_data, the caller begins to sleep by
calling wait_for_complete() and wait for the wake-up from calling
complete() in pm8001_mpi_set_nvmd_resp. In the current code,
the memcpy for response message buffer occurs after calling complete().
So, it is not protected by the use of wait_for_completion() and
complete().

Due to unexpected events (e.g., interrupt), if response buffer gets
freed before memcpy, the use-after-free error will occur.
To fix it, the complete() should be called after memcpy.

Signed-off-by: yuuzheng <yuuzheng@google.com>
Signed-off-by: Viswas G <Viswas.G@microchip.com>
Signed-off-by: Ruksar Devadi <Ruksar.devadi@microchip.com>
Signed-off-by: Radha Ramachandran <radha@google.com>
---
 drivers/scsi/pm8001/pm8001_hwi.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/pm8001/pm8001_hwi.c b/drivers/scsi/pm8001/pm8001_hwi.c
index 9e9a546da959..2054c2b03d92 100644
--- a/drivers/scsi/pm8001/pm8001_hwi.c
+++ b/drivers/scsi/pm8001/pm8001_hwi.c
@@ -3279,10 +3279,15 @@ pm8001_mpi_get_nvmd_resp(struct pm8001_hba_info *pm8001_ha, void *piomb)
 		pm8001_ha->memoryMap.region[NVMD].virt_ptr,
 		fw_control_context->len);
 	kfree(ccb->fw_control_context);
+	/* To avoid race condition, complete should be
+	 * called after the message is copied to
+	 * fw_control_context->usrAddr
+	 */
+	complete(pm8001_ha->nvmd_completion);
+	PM8001_MSG_DBG(pm8001_ha, pm8001_printk("Set nvm data complete!\n"));
 	ccb->task = NULL;
 	ccb->ccb_tag = 0xFFFFFFFF;
 	pm8001_tag_free(pm8001_ha, tag);
-	complete(pm8001_ha->nvmd_completion);
 }
 
 int pm8001_mpi_local_phy_ctl(struct pm8001_hba_info *pm8001_ha, void *piomb)
-- 
2.16.3