Re: [RFC PATCH v1.2] mm/damon/core: validate ranges in damon_set_regions()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Flawed Validation Logic for Empty and Inverted Regions
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commit 663c371bd35c3a6e3044a1a0a7c4a31852e3924f
Author: SJ Park <sj@kernel.org>

mm/damon/core: validate ranges in damon_set_regions()

This commit adds validation logic to damon_set_regions() to ensure that 
empty monitoring target regions are rejected. This prevents division-by-zero 
errors and sanity check warnings within the DAMON core logic.

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -358,6 +358,12 @@ int damon_set_regions(struct damon_target *t, struct damon_addr_range *ranges,
>  	unsigned int i;
>  	int err;
>  
> +	for (i = 0; i < nr_ranges; i++) {
> +		if (ALIGN_DOWN(ranges[i].start, min_region_sz) >=
> +				ALIGN(ranges[i].end, min_region_sz))
> +			return -EINVAL;
> +	}
> +

[Severity: Medium]
Does this validation logic correctly reject unaligned empty or inverted
ranges?

It looks like the alignment macros are applied before evaluating the bounds.
If a caller provides an unaligned empty range like [4097, 4097], ALIGN_DOWN 
makes the start 4096, and ALIGN makes the end 8192. This evaluates to 
4096 >= 8192, which is false, allowing the empty range to bypass the check 
and silently expand into a valid monitoring region.

Conversely, a page-aligned empty range like [4096, 4096] evaluates as 
4096 >= 4096 and is correctly rejected. Similarly, an inverted range like 
[4000, 3000] would align to [0, 4096) and be accepted.

Should the raw input bounds (ranges[i].start >= ranges[i].end) be validated
prior to applying the alignment macros?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260628165447.86217-1-sj@kernel.org?part=1