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 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. > >  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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