Re: [RFC PATCH 6.18.y 3/5] mm/damon/sysfs-schemes: read sysfs_filter->sz_range only once

[sashiko-bot@kernel.org]

> DAMON sysfs interface reads the user-provided size range arguments for
> hugepage_size type DAMOS filter twice.  Once for validation, and once
> again for assignments to the variable that will be passed to the core
> layer.  If the user updates the arguments in parallel, an invalid size
> range could be passed to the core layer.  Avoid it by doing the
> assignments first, and then validating the assigned variables before
> passing those to the core layer.
> 
> User impact of the bug should be trivial.  From the core layer's
> perspective, the invalid size range is not really invalid.  It just works
> as having a weird size range.  No critical issues such as a crash or a
> leak could happen.  And sane users ain't do such parallel arguments update
> anyway.  If they do, such racy behavior is arguably somewhat expected and
> deserved.  That said, there is no reason to keep such races.
> 
> Link: https://lore.kernel.org/20260914142327.92510-3-sj@kernel.org
> Fixes: ea1f204ba29a ("mm/damon/sysfs-schemes: add files for setting damos_filter->sz_range")
> Signed-off-by: SJ Park <sj@kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Cc: Brendan Higgins <brendan.higgins@linux.dev>
> Cc: David Gow <davidgow@davidgow.net>
> Cc: Usama Arif <usamaarif642@gmail.com>
> Cc: <stable@vger.kernel.org>
> (cherry picked from commit af19aff38d6faea35b10f26cca32d0e54f8aea5e)
> Signed-off-by: SJ Park <sj@kernel.org>

Sashiko has reviewed this patch and found no issues.

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