[PATCH 2/2] of: fdt: fix possible overflow during parsing of fdt

[Ahmad Fatoum]

Hello Abdelrahman,

Thanks for your patch.

On 12.11.24 17:20, Abdelrahman Youssef wrote:
> While fuzzing, the name marked by FDT_BEGIN_NODE sometimes extends beyond
> the struct block area, Causing a heap-overflow.
> 
> Since `maxlen` is an unsigned integer representing the length of name,
> It can be negative, So it overflows to large numbers, Causing strnlen()
> to overflow.
> 
> So we can just change the type of maxlen to signed and check if it's negative.
> 
> Signed-off-by: Abdelrahman Youssef <abdelrahmanyossef12 at gmail.com>
> ---

Changelog would be nice for future patches.
Also use -v2 instead of -2 as argument to git format-patch / git send-email
(or let b4 handle revision increment).

>  drivers/of/fdt.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index 2c3ea31394..13d0b8be54 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -176,7 +176,7 @@ static struct device_node *__of_unflatten_dtb(const void *infdt, int size,
>  	void *dt_strings;
>  	struct fdt_header f;
>  	int ret;
> -	unsigned int maxlen;
> +	int maxlen;
>  	const struct fdt_header *fdt = infdt;
>  
>  	ret = fdt_parse_header(infdt, size, &f);
> @@ -210,6 +210,12 @@ static struct device_node *__of_unflatten_dtb(const void *infdt, int size,
>  			maxlen = (unsigned long)fdt + f.off_dt_struct +
>  				f.size_dt_struct - (unsigned long)name;
>  
> +			if(maxlen < 0)
> +			{

Kernel coding style is space betewen if and (. Also move brace to same line as
the if statement. See the other if conditions in the file.

Cheers,
Ahmad

> +				ret = -ESPIPE;
> +				goto err;
> +			}
> +
>  			len = strnlen(name, maxlen + 1);
>  			if (len > maxlen) {
>  				ret = -ESPIPE;


-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |