Re: [PATCH] Remove redundant cleanup in ipmi_register_smi

From: Corey Minyard
Date: Wed Aug 22 2018 - 12:27:44 EST

On 08/21/2018 10:25 AM, Justin Ernst wrote:
When ipmi_register_smi fails, it performs a small cleanup routine
before returning its error value. In try_smi_init, on the condition that
ipmi_register_smi fails, ipmi_unregister_smi is called. ipmi_unregister_smi
performs the same cleanup routine as ipmi_register_smi. This results in
a kernel NULL pointer dereference. Removing the cleanup routine in
ipmi_register_smi results in proper cleanup of a ipmi_register_smi failure.

This is almost certainly wrong. If ipmi_register_smi() fails, the calling code shouldn't call

However, I think I know what is going wrong. ipmi_register_smi() can fail after the interface
is initialized, if so the registering code will think it is registered and call ipmi_unregister_smi()
on a failure. I'll send a patch for this.


Cc: Corey Minyard <minyard@xxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Jeremy Kerr <jk@xxxxxxxxxx>
Cc: openipmi-developer@xxxxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Russ Anderson <russ.anderson@xxxxxxx>
Acked-by: Andrew Banman <abanman@xxxxxxx>
Signed-off-by: Justin Ernst <justin.ernst@xxxxxxx>
drivers/char/ipmi/ipmi_msghandler.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
index 51832b8a2c62..3b0b50c4f064 100644
--- a/drivers/char/ipmi/ipmi_msghandler.c
+++ b/drivers/char/ipmi/ipmi_msghandler.c
@@ -3395,12 +3395,12 @@ int ipmi_register_smi(const struct ipmi_smi_handlers *handlers,
if (rv) {
- ipmi_bmc_unregister(intf);
- list_del_rcu(&intf->link);
+ /*
+ * ipmi_unregister_smi must be called to clean up after
+ * failure. We unlock the mutex to allow ipmi_unregister_smi
+ * to lock it and perform cleanup.
+ */
- synchronize_srcu(&ipmi_interfaces_srcu);
- cleanup_srcu_struct(&intf->users_srcu);
- kref_put(&intf->refcount, intf_free);
} else {
* Keep memory order straight for RCU readers. Make