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

[SJ Park <sj@kernel.org>]

On Sun, 28 Jun 2026 17:09:21 +0000 sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] Flawed Validation Logic for Empty and Inverted Regions
> --
> 
> 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?

Sashiko's behavior expectation is correct.  And that could be not really good
user experience.  But I think that's what we could improve in future unless it
introduces too much complexity, rather than somewhat need to be implemented
right now blocking this fix.

So, no blocker.  I will consider improving the user experience as a future
work.


Thanks,
SJ

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