Re: [PATCH] mm/gup_test: reject wrapped user ranges

["David Hildenbrand (Arm)" <david@kernel.org>]

On 6/9/26 02:48, Samuel Moelius wrote:
> gup_test accepts an address and size from the debugfs ioctl and
> repeatedly compares against addr + size. If that addition wraps, the
> loop can be skipped and the ioctl returns success with size rewritten to
> zero.

Yeah, it's only used for testing and (a) not expected to be included in
production kernels or of so (b) only accessible to root.

So we didn't particularly care about making this interface watertight.

> 
> Compute the end address once with overflow checking and use that checked
> end for the loop bounds.
> 
> Assisted-by: Codex:gpt-5.5-cyber-preview
> Signed-off-by: Samuel Moelius <sam.moelius@trailofbits.com>
> ---
>  mm/gup_test.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/gup_test.c b/mm/gup_test.c
> index 9dd48db897b9..eb4c9cda16ed 100644
> --- a/mm/gup_test.c
> +++ b/mm/gup_test.c
> @@ -105,11 +105,15 @@ static int __gup_test_ioctl(unsigned int cmd,
>  	unsigned long i, nr_pages, addr, next;
>  	long nr;
>  	struct page **pages;
> +	unsigned long end;
>  	int ret = 0;
>  	bool needs_mmap_lock =
>  		cmd != GUP_FAST_BENCHMARK && cmd != PIN_FAST_BENCHMARK;
>  
> -	if (gup->size > ULONG_MAX)
> +	if (gup->addr > ULONG_MAX || gup->size > ULONG_MAX)
> +		return -EINVAL;
> +	if (check_add_overflow((unsigned long)gup->addr,
> +			       (unsigned long)gup->size, &end))
>  		return -EINVAL;
>  
>  	nr_pages = gup->size / PAGE_SIZE;
> @@ -125,13 +129,13 @@ static int __gup_test_ioctl(unsigned int cmd,
>  	i = 0;
>  	nr = gup->nr_pages_per_call;
>  	start_time = ktime_get();
> -	for (addr = gup->addr; addr < gup->addr + gup->size; addr = next) {
> +	for (addr = gup->addr; addr < end; addr = next) {
>  		if (nr != gup->nr_pages_per_call)
>  			break;
>  
>  		next = addr + nr * PAGE_SIZE;
> -		if (next > gup->addr + gup->size) {
> -			next = gup->addr + gup->size;
> +		if (next > end) {
> +			next = end;
>  			nr = (next - addr) / PAGE_SIZE;
>  		}
>  

LGTM

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David