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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@tobin.cc> Signed-off-by: Kalle Valo <kvalo@codeaurora.org> |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.