rsi: Remove stack VLA usage

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>

diff --git a/drivers/net/wireless/rsi/rsi_91x_sdio.c b/drivers/net/wireless/rsi/rsi_91x_sdio.c
index 98c7d1dae18e12d65b8e4095dce4bdbda4f1611e..13705fca59dd071cf4af071f5919db1e7ebf48fa 100644 (file)
--- 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