Re: [PATCH 04/12] mtd: rawnand: brcmnand: Fix potential out-of-bounds access in oob write

[Miquel Raynal]

Hi William,

william.zhang@xxxxxxxxxxxx wrote on Tue,  6 Jun 2023 16:12:44 -0700:

> When the oob buffer length is not in multiple of words, the oob write
> function does out-of-bounds read on the oob source buffer at the last
> iteration. Fix that by always checking length limit on the oob buffer
> read and fill with 0xff when reaching the end of the buffer to the oob
> registers.
> 
> Fixes: 27c5b17cd1b1 ("mtd: nand: add NAND driver "library" for Broadcom STB NAND controller")
> Signed-off-by: William Zhang <william.zhang@xxxxxxxxxxxx>
> Reviewed-by: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx>
> ---
> 
>  drivers/mtd/nand/raw/brcmnand/brcmnand.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mtd/nand/raw/brcmnand/brcmnand.c b/drivers/mtd/nand/raw/brcmnand/brcmnand.c
> index 20832857c4aa..d920e88c7f5b 100644
> --- a/drivers/mtd/nand/raw/brcmnand/brcmnand.c
> +++ b/drivers/mtd/nand/raw/brcmnand/brcmnand.c
> @@ -1486,10 +1486,10 @@ static int write_oob_to_regs(struct brcmnand_controller *ctrl, int i,
>  
>  	for (j = 0; j < tbytes; j += 4)
>  		oob_reg_write(ctrl, j,
> -				(oob[j + 0] << 24) |
> -				(oob[j + 1] << 16) |
> -				(oob[j + 2] <<  8) |
> -				(oob[j + 3] <<  0));
> +				(((j < tbytes) ? oob[j] : 0xff) << 24) |
> +				(((j + 1 < tbytes) ? oob[j + 1] : 0xff) << 16) |
> +				(((j + 2 < tbytes) ? oob[j + 2] : 0xff) << 8) |
> +				((j + 3 < tbytes) ? oob[j + 3] : 0xff));

This is a lot of additional operations which most of the time are not
relevant. I would instead got for one less iteration in the for loop
when there is unaligned data, and then dedicated if/else to fill the
missing bytes.

>  	return tbytes;
>  }
>  


Thanks,
Miquèl