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SubjectRe: [PATCH] Remove redundant cleanup in ipmi_register_smi
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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
ipmi_unregister_smi().

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.

-corey

>
> Cc: Corey Minyard <minyard@acm.org>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Jeremy Kerr <jk@ozlabs.org>
> Cc: openipmi-developer@lists.sourceforge.net
> Cc: linux-kernel@vger.kernel.org
> Cc: Russ Anderson <russ.anderson@hpe.com>
> Acked-by: Andrew Banman <abanman@hpe.com>
> Signed-off-by: Justin Ernst <justin.ernst@hpe.com>
> ---
> 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,
>
> out:
> 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.
> + */
> mutex_unlock(&ipmi_interfaces_mutex);
> - 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


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