Re: [v2] rsi: Remove stack VLA usage

[Kalle Valo]

"Tobin C. Harding"  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 

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

[PATCH v2] rsi: Remove stack VLA usage

[Tobin C. Harding]

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 
---

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(-)

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 0x0416
-- 
2.7.4