From 7e2ed8a29427af534bf2cb9b8bc51762b8b6e654 Mon Sep 17 00:00:00 2001 From: SeongJae Park Date: Thu, 28 May 2026 17:01:02 -0700 Subject: [PATCH] mm/damon/reclaim: handle ctx allocation failure Patch series "mm/damon/{reclaim,lru_sort}: handle ctx allocation failures". DAMON_RECLAIM and DAMON_LRU_SORT could dereference NULL pointers if their damon_ctx object allocations fail. The bugs are expected to happen infrequently because the allocations are arguably too small to fail on common setups. But theoretically they are possible and the consequences are bad. Fix those. The issues were discovered [1] by Sashiko. This patch (of 2): DAMON_RECLAIM allocates the damon_ctx object for its kdamond in its init function. damon_reclaim_enabled_store() wrongly assumes the allocation will always succeed once tried. If the damon_ctx allocation was failed, therefore, code execution reaches to damon_commit_ctx() while 'ctx' is NULL. As a result, it dereferences the NULL 'ctx' pointer. Avoid the NULL dereference by returning -ENOMEM if 'ctx' is NULL. Link: https://lore.kernel.org/20260529000104.7006-2-sj@kernel.org Link: https://lore.kernel.org/20260419014800.877-1-sj@kernel.org [1] Fixes: 3f7a914ab9a5 ("mm/damon/reclaim: use damon_initialized()") Signed-off-by: SeongJae Park Cc: # 6.18.x Signed-off-by: Andrew Morton --- mm/damon/reclaim.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/damon/reclaim.c b/mm/damon/reclaim.c index fe7fce26cf6c..96f6dfc28eae 100644 --- a/mm/damon/reclaim.c +++ b/mm/damon/reclaim.c @@ -339,6 +339,10 @@ static int damon_reclaim_enabled_store(const char *val, if (!damon_initialized()) return 0; + /* damon_modules_new_paddr_ctx_target() in the init function failed. */ + if (!ctx) + return -ENOMEM; + return damon_reclaim_turn(enabled); }