[PATCH v1] mmc: fix signed vs unsigned compare in read check in _spl_load()

[Sean Anderson]

Hi Franco,

On 7/30/24 09:30, Franco Venturi wrote:
> Fix signed vs unsigned compare in read check in _spl_load()
> 
> Issue: when info->read() returns a negative value because of an error,
>         the comparison of 'read' (signed) with 'sizeof(*header)'
>         (unsigned silently converts the negative value into a very
>         large unsigned value and the check on the error condition
>         always return false, i.e. the error is not detected
> Symptoms: if spl_load_image_fat() is unable to find the file 'uImage',
>            the SPL phase of the boot process just hangs after displaying
>            the following line:
>            Trying to boot from MMC1
> Fix: first check if 'read' is negative then check its value against
>       'sizeof(*header)'
> Reference: https://stackoverflow.com/questions/17293749/sizeof-operator-in-if-statement
> 
> Signed-off-by: Franco Venturi <fventuri at comcast.net>
> ---
> 
>   include/spl_load.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/spl_load.h b/include/spl_load.h
> index 1c2b296c0a..1e05599d29 100644
> --- a/include/spl_load.h
> +++ b/include/spl_load.h
> @@ -22,7 +22,7 @@ static inline int _spl_load(struct spl_image_info *spl_image,
>   
>   	read = info->read(info, offset, ALIGN(sizeof(*header),
>   					      spl_get_bl_len(info)), header);
> -	if (read < sizeof(*header))
> +	if (read < 0 || read < sizeof(*header))
>   		return -EIO;
>   
>   	if (image_get_magic(header) == FDT_MAGIC) {

Since read and int and sizeof(*header) < INT_MAX, I think the best solution is
to cast the latter to an int.

--Sean