From 2f4cc18b716acd6f00f029f2c03fb8cd8357796a Mon Sep 17 00:00:00 2001 From: SeongJae Park Date: Wed, 26 Feb 2025 22:49:14 +0900 Subject: [PATCH] mm/damon/core: avoid overflow in damon_feed_loop_next_input() BugLink: https://bugs.launchpad.net/bugs/2100292 commit 4401e9d10ab0281a520b9f8c220f30f60b5c248f upstream. damon_feed_loop_next_input() is inefficient and fragile to overflows. Specifically, 'score_goal_diff_bp' calculation can overflow when 'score' is high. The calculation is actually unnecessary at all because 'goal' is a constant of value 10,000. Calculation of 'compensation' is again fragile to overflow. Final calculation of return value for under-achiving case is again fragile to overflow when the current score is under-achieving the target. Add two corner cases handling at the beginning of the function to make the body easier to read, and rewrite the body of the function to avoid overflows and the unnecessary bp value calcuation. Link: https://lkml.kernel.org/r/20241031161203.47751-1-sj@kernel.org Fixes: 9294a037c015 ("mm/damon/core: implement goal-oriented feedback-driven quota auto-tuning") Signed-off-by: SeongJae Park Reported-by: Guenter Roeck Closes: https://lore.kernel.org/944f3d5b-9177-48e7-8ec9-7f1331a3fea3@roeck-us.net Tested-by: Guenter Roeck Cc: [6.8.x] Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman CVE-2024-50270 Signed-off-by: Koichiro Den Signed-off-by: Stefan Bader --- mm/damon/core.c | 28 +++++++++++++++++++++------- 1 file changed, 21 insertions(+), 7 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index 6612d1318901..bce6582f0647 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -1070,17 +1070,31 @@ static unsigned long damon_feed_loop_next_input(unsigned long last_input, unsigned long score) { const unsigned long goal = 10000; - unsigned long score_goal_diff = max(goal, score) - min(goal, score); - unsigned long score_goal_diff_bp = score_goal_diff * 10000 / goal; - unsigned long compensation = last_input * score_goal_diff_bp / 10000; /* Set minimum input as 10000 to avoid compensation be zero */ const unsigned long min_input = 10000; + unsigned long score_goal_diff, compensation; + bool over_achieving = score > goal; - if (goal > score) + if (score == goal) + return last_input; + if (score >= goal * 2) + return min_input; + + if (over_achieving) + score_goal_diff = score - goal; + else + score_goal_diff = goal - score; + + if (last_input < ULONG_MAX / score_goal_diff) + compensation = last_input * score_goal_diff / goal; + else + compensation = last_input / goal * score_goal_diff; + + if (over_achieving) + return max(last_input - compensation, min_input); + if (last_input < ULONG_MAX - compensation) return last_input + compensation; - if (last_input > compensation + min_input) - return last_input - compensation; - return min_input; + return ULONG_MAX; } /* Shouldn't be called if quota->ms, quota->sz, and quota->get_score unset */