linux-kernel - Re: [PATCH v2] ipmi: Prevent use-after-free in deliver

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Message-ID: <3f6be669-0a5f-5b82-aa68-14c97c7df52a@acm.org>
Date:   Sat, 19 Jan 2019 19:30:59 -0600
From:   Corey Minyard <minyard@....org>
To:     Fred Klassen <fklassen@...neta.com>,
        "Arnd Bergmann (supporter:CHAR and MISC DRIVERS)" <arnd@...db.de>,
        "Greg Kroah-Hartman (supporter:CHAR and MISC DRIVERS)" 
        <gregkh@...uxfoundation.org>,
        "moderated list:IPMI SUBSYSTEM" 
        <openipmi-developer@...ts.sourceforge.net>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] ipmi: Prevent use-after-free in deliver_response

On 1/19/19 4:28 PM, Fred Klassen wrote:
> Some IPMI modules (e.g. ibmpex_msg_handler()) will have ipmi_usr_hdlr
> handlers that call ipmi_free_recv_msg() directly. This will essentially
> kfree(msg), leading to use-after-free.
>
> This does not happen in the ipmi_devintf module, which will queue the
> message and run ipmi_free_recv_msg() later.

Yeah, this is better style, if nothing else.

I assume you want this for 5.0., right?

-corey

> BUG: KASAN: use-after-free in deliver_response+0x12f/0x1b0
> Read of size 8 at addr ffff888a7bf20018 by task ksoftirqd/3/27
> CPU: 3 PID: 27 Comm: ksoftirqd/3 Tainted: G           O      4.19.11-amd64-ani99-debug #12.0.1.601133+pv
> Hardware name: AppNeta r1000/X11SPW-TF, BIOS 2.1a-AP 09/17/2018
> Call Trace:
> dump_stack+0x92/0xeb
> print_address_description+0x73/0x290
> kasan_report+0x258/0x380
> deliver_response+0x12f/0x1b0
> ? ipmi_free_recv_msg+0x50/0x50
> deliver_local_response+0xe/0x50
> handle_one_recv_msg+0x37a/0x21d0
> handle_new_recv_msgs+0x1ce/0x440
> ...
>
> Allocated by task 9885:
> kasan_kmalloc+0xa0/0xd0
> kmem_cache_alloc_trace+0x116/0x290
> ipmi_alloc_recv_msg+0x28/0x70
> i_ipmi_request+0xb4a/0x1640
> ipmi_request_settime+0x1b8/0x1e0
> ...
>
> Freed by task 27:
> __kasan_slab_free+0x12e/0x180
> kfree+0xe9/0x280
> deliver_response+0x122/0x1b0
> deliver_local_response+0xe/0x50
> handle_one_recv_msg+0x37a/0x21d0
> handle_new_recv_msgs+0x1ce/0x440
> tasklet_action_common.isra.19+0xc4/0x250
> __do_softirq+0x11f/0x51f
>
> Fixes: e86ee2d44b44 ("ipmi: Rework locking and shutdown for hot remove")
> Cc: stable@...r.kernel.org
> Signed-off-by: Fred Klassen <fklassen@...neta.com>
> ---
> drivers/char/ipmi/ipmi_msghandler.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
> index 7fc9612070a1..fbf93c2d6c05 100644
> --- a/drivers/char/ipmi/ipmi_msghandler.c
> +++ b/drivers/char/ipmi/ipmi_msghandler.c
> @@ -883,7 +883,7 @@ static int deliver_response(struct ipmi_smi *intf, struct ipmi_recv_msg *msg)
>
> 		if (user) {
> 			user->handler->ipmi_recv_hndl(msg, user->handler_data);
> -			release_ipmi_user(msg->user, index);
> +			release_ipmi_user(user, index);
> 		} else {
> 			/* User went away, give up. */
> 			ipmi_free_recv_msg(msg);