Re: [RFC PATCH 3/8] mm/damon/sysfs: remove duplicated commit input validity check

[SJ Park <sj@kernel.org>]

On Wed, 01 Jul 2026 15:29:02 +0000 sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] Removing the explicit `test_ctx` parameter validation in `damon_sysfs_commit_input` exposes an underlying flaw in `damon_commit_ctx`, allowing invalid sysfs inputs to corrupt the running context and terminate the background kdamond thread.
> --
> 
> Note: Due to system limitations regarding exact code recitation, this report
> uses a free-form summary of the issue rather than inline patch quoting.
> 
> commit bec0828fbe945683bcef8cfdb56247414f2510d8
> Author: SJ Park <sj@kernel.org>
> Subject: mm/damon/sysfs: remove duplicated commit input validity check
> 
> This commit removes the explicit test_ctx validation inside
> damon_sysfs_commit_input(), assuming the same validation logic is safely
> embedded inside damon_commit_ctx().
> 
> [Severity: High]
> Does removing the sysfs-level test_ctx wrapper expose the running context to
> corruption from invalid user inputs?
> 
> In mm/damon/core.c:damon_commit_ctx(), it appears the underlying validation
> logic tests 'dst' against the temporary 'test_ctx' instead of testing the
> new 'src' parameters:
> 
> damon_commit_ctx()
>    err = __damon_commit_ctx(test_ctx, dst);
>    if (err)
>        goto out;
>    err = __damon_commit_ctx(dst, src);
> 
> Because damon_sysfs_commit_input() now relies entirely on damon_commit_ctx()
> for validation, what happens if invalid configuration parameters (such as a
> min_region_sz that is not a power of 2) are passed via the sysfs interface?
> 
> It looks like __damon_commit_ctx(dst, src) will fail halfway through, returning
> -EINVAL but leaving the running context with maybe_corrupted = true. Can this
> cause the background kdamond_fn thread to silently abort without recovering,
> effectively resulting in a denial of service for the monitoring session?

Correct.  I will fix damon_commit_ctx() side validation in the next revision.


Thanks,
SJ

[...]