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

[sashiko-bot@kernel.org]

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.
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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?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260701144815.113325-1-sj@kernel.org?part=3