linux-kernel - Re: [PATCH 3.2 31/34] rtl8192ce: Fix null dereference in watchdog

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Date:	Fri, 16 May 2014 09:20:25 -0500
From:	Larry Finger <Larry.Finger@...inger.net>
To:	Ben Hutchings <ben@...adent.org.uk>, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	Chaoming Li <chaoming_li@...lsil.com.cn>,
	Dmitry Semyonov <linulin@...il.com>
Subject: Re: [PATCH 3.2 31/34] rtl8192ce: Fix null dereference in watchdog

On 05/16/2014 07:47 AM, Ben Hutchings wrote:
> 3.2.59-rc1 review patch.  If anyone has any objections, please let me know.
>
> ------------------
>
> From: Ben Hutchings <ben@...adent.org.uk>
>
> Dmitry Semyonov reported that after upgrading from 3.2.54 to
> 3.2.57 the rtl8192ce driver will crash when its interface is brought
> up.  The oops message shows:
>
> [ 1833.611397] BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
> [ 1833.611455] IP: [<ffffffffa0410c6a>] rtl92ce_update_hal_rate_tbl+0x29/0x4db [rtl8192ce]
> ...
> [ 1833.613326] Call Trace:
> [ 1833.613346]  [<ffffffffa02ad9c6>] ? rtl92c_dm_watchdog+0xd0b/0xec9 [rtl8192c_common]
> [ 1833.613391]  [<ffffffff8105b5cf>] ? process_one_work+0x161/0x269
> [ 1833.613425]  [<ffffffff8105c598>] ? worker_thread+0xc2/0x145
> [ 1833.613458]  [<ffffffff8105c4d6>] ? manage_workers.isra.25+0x15b/0x15b
> [ 1833.613496]  [<ffffffff8105f6d9>] ? kthread+0x76/0x7e
> [ 1833.613527]  [<ffffffff81356b74>] ? kernel_thread_helper+0x4/0x10
> [ 1833.613563]  [<ffffffff8105f663>] ? kthread_worker_fn+0x139/0x139
> [ 1833.613598]  [<ffffffff81356b70>] ? gs_change+0x13/0x13
>
> Disassembly of rtl92ce_update_hal_rate_tbl() shows that the 'sta'
> parameter was null.  None of the changes to the rtlwifi family between
> 3.2.54 and 3.2.57 seem to directly cause this, and reverting commit
> f78bccd79ba3 ('rtlwifi: rtl8192ce: Fix too long disable of IRQs')
> doesn't fix it.
>
> rtl92c_dm_watchdog() calls rtl92ce_update_hal_rate_tbl() via
> rtl92c_dm_refresh_rate_adaptive_mask(), which does not appear in the
> call trace as it was inlined.  That function has been completely
> removed upstream which may explain why this crash wasn't seen there.
>
> I'm not sure that it is sensible to completely remove
> rtl92c_dm_refresh_rate_adaptive_mask() without making other
> compensating changes elsewhere, so try to work around this for 3.2 by
> checking for a null pointer in rtl92c_dm_refresh_rate_adaptive_mask()
> and then skipping the call to rtl92ce_update_hal_rate_tbl().
>
> References: https://bugs.debian.org/745137
> References: https://bugs.debian.org/745462
> Reported-by: Dmitry Semyonov <linulin@...il.com>
> Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
> Cc: Larry Finger <Larry.Finger@...inger.net>
> Cc: Chaoming Li <chaoming_li@...lsil.com.cn>
> ---

Ben,

Your fix is a reasonable workaround. I have no explanation for this NULL pointer 
dereference to suddenly appear; however, the pointer should have been checked 
from the start.

Thanks,

Larry

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