Re: [PATCH v2] of: fdt: fix possible overflow during parsing of fdt

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Abdelrahman,

Thanks for your patch.

On 12.11.24 20:10, 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@gmail.com>
> ---

Changelog would've been nice. This also should have been v3 not v2.

>  drivers/of/fdt.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index 2c3ea31394..d8d8a4922c 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 +210,11 @@ 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) {
> +				ret = -ESPIPE;
> +				goto err;
> +			}
> +
>  			len = strnlen(name, maxlen + 1);

Hmm is this + 1 correct? I am wondering if we should be dropping
the + 1 here and make it maxlen <= 0 above.

What do you think?

Cheers,
Ahmad

>  			if (len > maxlen) {>  				ret = -ESPIPE;


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