| Message ID | 1521081085-16404-1-git-send-email-me@tobin.cc (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 44f98a9332e4b97b0215a1c38e647bc0cd8e5a5f |
| Delegated to: | Kalle Valo |
| Headers | show |
"Tobin C. Harding" <me@tobin.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@tobin.cc> Patch applied to wireless-drivers-next.git, thanks. 44f98a9332e4 rsi: Remove stack VLA usage
diff --git a/drivers/net/wireless/rsi/rsi_91x_sdio.c b/drivers/net/wireless/rsi/rsi_91x_sdio.c index 98c7d1dae18e..13705fca59dd 100644 --- a/drivers/net/wireless/rsi/rsi_91x_sdio.c +++ b/drivers/net/wireless/rsi/rsi_91x_sdio.c @@ -576,7 +576,7 @@ static int rsi_sdio_load_data_master_write(struct rsi_hw *adapter, { u32 num_blocks, offset, i; u16 msb_address, lsb_address; - u8 temp_buf[block_size]; + u8 *temp_buf; int status; num_blocks = instructions_sz / block_size; @@ -585,11 +585,15 @@ static int rsi_sdio_load_data_master_write(struct rsi_hw *adapter, rsi_dbg(INFO_ZONE, "ins_size: %d, num_blocks: %d\n", instructions_sz, num_blocks); + temp_buf = kmalloc(block_size, GFP_KERNEL); + if (!temp_buf) + return -ENOMEM; + /* Loading DM ms word in the sdio slave */ status = rsi_sdio_master_access_msword(adapter, msb_address); if (status < 0) { rsi_dbg(ERR_ZONE, "%s: Unable to set ms word reg\n", __func__); - return status; + goto out_free; } for (offset = 0, i = 0; i < num_blocks; i++, offset += block_size) { @@ -601,7 +605,7 @@ static int rsi_sdio_load_data_master_write(struct rsi_hw *adapter, temp_buf, block_size); if (status < 0) { rsi_dbg(ERR_ZONE, "%s: failed to write\n", __func__); - return status; + goto out_free; } rsi_dbg(INFO_ZONE, "%s: loading block: %d\n", __func__, i); base_address += block_size; @@ -616,7 +620,7 @@ static int rsi_sdio_load_data_master_write(struct rsi_hw *adapter, rsi_dbg(ERR_ZONE, "%s: Unable to set ms word reg\n", __func__); - return status; + goto out_free; } } } @@ -632,12 +636,16 @@ static int rsi_sdio_load_data_master_write(struct rsi_hw *adapter, temp_buf, instructions_sz % block_size); if (status < 0) - return status; + goto out_free; rsi_dbg(INFO_ZONE, "Written Last Block in Address 0x%x Successfully\n", offset | RSI_SD_REQUEST_MASTER); } - return 0; + + status = 0; +out_free: + kfree(temp_buf); + return status; } #define FLASH_SIZE_ADDR 0x04000016
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> --- This applies onto tip of wireless-drivers next, commit (28bf8312a983 mwifiex: get_channel from firmware v2: - Use kmalloc instead of #define (suggested by Larry) - (Apply on top of wireless-drivers-next tree) - (Fix up user name on patchwork.kernel.org) drivers/net/wireless/rsi/rsi_91x_sdio.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-)