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Date: Tue, 27 Mar 2018 08:04:53 +0000 (UTC)
From: Kalle Valo <kvalo@...eaurora.org>
To: "Tobin C. Harding" <me@...in.cc>
Cc: "Tobin C. Harding" <me@...in.cc>, kernel-hardening@...ts.openwall.com,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
linux-wireless@...r.kernel.org, Tycho Andersen <tycho@...ho.ws>,
Kees Cook <keescook@...omium.org>, Larry Finger <Larry.Finger@...inger.net>
Subject: Re: [v2] rsi: Remove stack VLA usage
"Tobin C. Harding" <me@...in.cc> wrote:
> The use of stack Variable Length Arrays needs to be avoided, as they
> can be a vector for stack exhaustion, which can be both a runtime bug
> (kernel Oops) or a security flaw (overwriting memory beyond the
> stack). Also, in general, as code evolves it is easy to lose track of
> how big a VLA can get. Thus, we can end up having runtime failures
> that are hard to debug. As part of the directive[1] to remove all VLAs
> from the kernel, and build with -Wvla.
>
> Currently rsi code uses a VLA based on a function argument to
> `rsi_sdio_load_data_master_write()`. The function call chain is
>
> Both these functions
>
> rsi_sdio_reinit_device()
> rsi_probe()
>
> start the call chain:
>
> rsi_hal_device_init()
> rsi_load_fw()
> auto_fw_upgrade()
> ping_pong_write()
> rsi_sdio_load_data_master_write()
>
> [Without familiarity with the code] it appears that none of the 4 locks
>
> mutex
> rx_mutex
> tx_mutex
> tx_bus_mutex
>
> are held when `rsi_sdio_load_data_master_write()` is called. It is therefore
> safe to use kmalloc with GFP_KERNEL.
>
> We can avoid using the VLA by using `kmalloc()` and free'ing the memory on all
> exit paths.
>
> Change buffer from 'u8 array' to 'u8 *'. Call `kmalloc()` to allocate memory for
> the buffer. Using goto statement to call `kfree()` on all return paths.
>
> It can be expected that this patch will result in a small increase in overhead
> due to the use of `kmalloc()` however this code is only called on initialization
> (and re-initialization) so this overhead should not degrade performance.
>
> [1] https://lkml.org/lkml/2018/3/7/621
>
> Signed-off-by: Tobin C. Harding <me@...in.cc>
Patch applied to wireless-drivers-next.git, thanks.
44f98a9332e4 rsi: Remove stack VLA usage
--
https://patchwork.kernel.org/patch/10283841/
https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
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