[PATCH v2] ipmi: si: Fix NULL pointer dereference after failed registration

[Seiji Nishikawa]

try_smi_init() allocates new_smi->si_sm and later calls
ipmi_register_smi_mod(), which maps to ipmi_add_smi().

During ipmi_add_smi(), the upper IPMI message handler obtains the
initial BMC device information through __bmc_get_device_id(). This can
fail if the BMC does not return a successful response to the Get Device
ID command.

When the BMC returns a nonzero completion code, the device-id helper
retries the command and eventually returns -EIO if the device ID still
cannot be fetched.

On this failure path, ipmi_add_smi() logs "Unable to get the device id"
and goes to out_err_started, where it invokes the lower driver's
shutdown callback. try_smi_init() then logs the returned registration
failure:

 ipmi_si IPI0001:00: IPMI message handler: Unable to get the device id: -5
 ipmi_si IPI0001:00: Unable to register device: error -5

For ipmi_si, the shutdown callback is shutdown_smi(), which cleans up
the SI state machine data, frees smi_info->si_sm, and sets
smi_info->si_sm and smi_info->intf to NULL.

However, intf->in_shutdown is not set on this failed-registration
rollback path. Therefore, the asynchronous redo_bmc_reg work item can
still retry BMC device-id probing after the lower driver has already
cleared its SI state machine data. In the observed case, that retry path
reached start_next_msg(), which passed the NULL smi_info->si_sm pointer
to the selected KCS state machine handler:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
Workqueue: events redo_bmc_reg [ipmi_msghandler]
RIP: start_kcs_transaction+0x2c/0x190 [ipmi_si]
Call Trace:
 start_next_msg+0x50/0x80 [ipmi_si]
 check_start_timer_thread.part.9+0x3b/0x50 [ipmi_si]
 sender+0x69/0x80 [ipmi_si]
 i_ipmi_request+0x2ac/0x9d0 [ipmi_msghandler]
 __get_device_id.isra.29+0xaa/0x180 [ipmi_msghandler]
 __bmc_get_device_id+0xef/0x950 [ipmi_msghandler]
 redo_bmc_reg+0x52/0x60 [ipmi_msghandler]
 process_one_work+0x1a7/0x360

Set intf->in_shutdown on the out_err_started path before invoking the
lower driver's shutdown callback. This prevents later redo_bmc_reg
retries from using an interface whose lower driver state has been
cleaned up, and applies the same shutdown state to other IPMI interfaces
as well.

Signed-off-by: Seiji Nishikawa <snishika@xxxxxxxxxx>
---
Thanks, I agree. I moved the fix to the ipmi_add_smi() rollback path in v2
and dropped the SI-side NULL checks.

Changes in v2:
- Move the fix to ipmi_add_smi() by setting intf->in_shutdown on the
  out_err_started path, as suggested by Corey.
- Drop the NULL checks in ipmi_si_intf.c.

 drivers/char/ipmi/ipmi_msghandler.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
index ab4c85f3d6fe..8d9f2e647d9b 100644
--- a/drivers/char/ipmi/ipmi_msghandler.c
+++ b/drivers/char/ipmi/ipmi_msghandler.c
@@ -3757,6 +3757,7 @@ int ipmi_add_smi(struct module         *owner,
  out_err_bmc_reg:
 	ipmi_bmc_unregister(intf);
  out_err_started:
+	intf->in_shutdown = true;
 	if (intf->handlers->shutdown)
 		intf->handlers->shutdown(intf->send_info);
  out_err:
-- 
2.54.0