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Subject[PATCH v2] rsi: Remove stack VLA usage
Date
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(-)

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
--
2.7.4
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