Re: [PATCH] ALSA: wavefront: Fix integer overflow in sample size validation

[Takashi Iwai <tiwai@suse.de>]

On Tue, 04 Nov 2025 15:10:18 +0100,
moonafterrain@outlook.com wrote:
> 
> From: Junrui Luo <moonafterrain@outlook.com>
> 
> The wavefront_send_sample() function has an integer overflow issue
> when validating sample size. The header->size field is u32 but gets
> cast to int for comparison with dev->freemem
> 
> Fix by using unsigned comparison to avoid integer overflow.

This is not really a right fix, unfortunately.
wavefront_freemem() itself can return a negative value, and the cast
would ignore it.

A better alternative could be something like:
	if (dev->freemem < 0 || dev->freemem < header->size) {
so that the cast can be dropped to be compared as unsigned
implicitly.

Not sure whether this still triggers some warnings in the recent
compilers, though.  Need testing.


thanks,

Takashi

> 
> Reported-by: Yuhao Jiang <danisjiang@gmail.com>
> Reported-by: Junrui Luo <moonafterrain@outlook.com>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Cc: stable@vger.kernel.org
> Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
> ---
>  sound/isa/wavefront/wavefront_synth.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/isa/wavefront/wavefront_synth.c b/sound/isa/wavefront/wavefront_synth.c
> index cd5c177943aa..4a8c507eae71 100644
> --- a/sound/isa/wavefront/wavefront_synth.c
> +++ b/sound/isa/wavefront/wavefront_synth.c
> @@ -950,9 +950,9 @@ wavefront_send_sample (snd_wavefront_t *dev,
>  	if (header->size) {
>  		dev->freemem = wavefront_freemem (dev);
>  
> -		if (dev->freemem < (int)header->size) {
> +		if ((unsigned int)dev->freemem < header->size) {
>  			dev_err(dev->card->dev,
> -				"insufficient memory to load %d byte sample.\n",
> +				"insufficient memory to load %u byte sample.\n",
>  				header->size);
>  			return -ENOMEM;
>  		}
> -- 
> 2.51.1.dirty
>