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Date:   Wed, 14 Mar 2018 07:09:57 +1100
From:   "Tobin C. Harding" <me@tobin.cc>
To:     Larry Finger <Larry.Finger@lwfinger.net>
Cc:     Kalle Valo <kvalo@codeaurora.org>,
        kernel-hardening@lists.openwall.com, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, linux-wireless@vger.kernel.org,
        Tycho Andersen <tycho@tycho.ws>,
        Kees Cook <keescook@chromium.org>
Subject: Re: [RESEND PATCH] rsi: Remove stack VLA usage
Message-ID: <20180313200957.GJ8631@eros>
References: <1520819022-15238-1-git-send-email-me@tobin.cc>
 <ff9309bf-4c3d-b0f9-cdd0-429dacd3177b@lwfinger.net>
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On Sun, Mar 11, 2018 at 09:06:10PM -0500, Larry Finger wrote:
> On 03/11/2018 08:43 PM, Tobin C. Harding wrote:
> >The kernel would like to have all stack VLA usage removed[1].  rsi uses
> >a VLA based on 'blksize'.  Elsewhere in the SDIO code maximum block size
> >is defined using a magic number.  We can use a pre-processor defined
> >constant and declare the array to maximum size.  We add a check before
> >accessing the array in case of programmer error.
> >
> >[1]: https://lkml.org/lkml/2018/3/7/621
> >
> >Signed-off-by: Tobin C. Harding <me@tobin.cc>
> >---
> >
> >RESEND: add wireless mailing list to CC's (requested by Kalle)
> >
> >  drivers/net/wireless/rsi/rsi_91x_hal.c  | 13 +++++++------
> >  drivers/net/wireless/rsi/rsi_91x_sdio.c |  9 +++++++--
> >  2 files changed, 14 insertions(+), 8 deletions(-)
> >
> >diff --git a/drivers/net/wireless/rsi/rsi_91x_hal.c b/drivers/net/wireless/rsi/rsi_91x_hal.c
> >index 1176de646942..839ebdd602df 100644
> >--- a/drivers/net/wireless/rsi/rsi_91x_hal.c
> >+++ b/drivers/net/wireless/rsi/rsi_91x_hal.c
> >@@ -641,7 +641,7 @@ static int ping_pong_write(struct rsi_hw *adapter, u8 cmd, u8 *addr, u32 size)
> >  	u32 cmd_addr;
> >  	u16 cmd_resp, cmd_req;
> >  	u8 *str;
> >-	int status;
> >+	int status, ret;
> >  	if (cmd == PING_WRITE) {
> >  		cmd_addr = PING_BUFFER_ADDRESS;
> >@@ -655,12 +655,13 @@ static int ping_pong_write(struct rsi_hw *adapter, u8 cmd, u8 *addr, u32 size)
> >  		str = "PONG_VALID";
> >  	}
> >-	status = hif_ops->load_data_master_write(adapter, cmd_addr, size,
> >+	ret = hif_ops->load_data_master_write(adapter, cmd_addr, size,
> >  					    block_size, addr);
> >-	if (status) {
> >-		rsi_dbg(ERR_ZONE, "%s: Unable to write blk at addr %0x\n",
> >-			__func__, *addr);
> >-		return status;
> >+	if (ret) {
> >+		if (ret != -EINVAL)
> >+			rsi_dbg(ERR_ZONE, "%s: Unable to write blk at addr %0x\n",
> >+				__func__, *addr);
> >+		return ret;
> >  	}
> >  	status = bl_cmd(adapter, cmd_req, cmd_resp, str);
> >diff --git a/drivers/net/wireless/rsi/rsi_91x_sdio.c b/drivers/net/wireless/rsi/rsi_91x_sdio.c
> >index b0cf41195051..b766578b591a 100644
> >--- a/drivers/net/wireless/rsi/rsi_91x_sdio.c
> >+++ b/drivers/net/wireless/rsi/rsi_91x_sdio.c
> >@@ -20,6 +20,8 @@
> >  #include "rsi_common.h"
> >  #include "rsi_hal.h"
> >+#define RSI_MAX_BLOCK_SIZE 256
> >+
> >  /**
> >   * rsi_sdio_set_cmd52_arg() - This function prepares cmd 52 read/write arg.
> >   * @rw: Read/write
> >@@ -362,7 +364,7 @@ static int rsi_setblocklength(struct rsi_hw *adapter, u32 length)
> >  	rsi_dbg(INIT_ZONE, "%s: Setting the block length\n", __func__);
> >  	status = sdio_set_block_size(dev->pfunction, length);
> >-	dev->pfunction->max_blksize = 256;
> >+	dev->pfunction->max_blksize = RSI_MAX_BLOCK_SIZE;
> >  	adapter->block_size = dev->pfunction->max_blksize;
> >  	rsi_dbg(INFO_ZONE,
> >@@ -567,9 +569,12 @@ 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[RSI_MAX_BLOCK_SIZE];
> >  	int status;
> >+	if (block_size > RSI_MAX_BLOCK_SIZE)
> >+		return -EINVAL;
> >+
> >  	num_blocks = instructions_sz / block_size;
> >  	msb_address = base_address >> 16;
> 
> I am not giving this patch a negative review, but my solution to the same
> problem has been to change the on-stack array into a u8 pointer, use
> kmalloc() to assign the space, and then free that space at the end. That way
> large stack allocations are avoided, with a minimum of changes.

Your idea is better Larry, have you got a patch done already or do you
want me to knock one up?

thanks,
Tobin.