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b=QPBqAj1UYUg3nMWYne8Sya+MKgu4V7EeGKLthl0o51iCB0NAPgs7sQgaXh4Xw8fds 2SU98NaNJ6MzubLEcUwGsVNIrEl9fomH6UIR1GjgcAr0qzkjoKQCVU3SbfxYkY2vZ/ uf2IwjhSs2FLSovNyLMfQUDal9VQijGA5yBmyICBzrzdUi/jhDx/WSjrYUnfLhsc3c D0pPtbGN+xU9+tIGrC28zdpiWLbAFzGViZZ1ZbQB7/Z96r9ZVuZAw9JzvYt0FBTEXj 82ykqjvPVIW7xc+YYHt+LiyuD28YP5oqnjg/0115RkfzVYi01+0926YFH+/QpJMhFr WpIlklGViaYsA== From: SeongJae Park To: Andrew Morton Cc: Josh Law , "# 6 . 17 . x" , SeongJae Park , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v3 3/3] mm/damon/sysfs: check contexts->nr in repeat_call_fn Date: Sat, 21 Mar 2026 10:54:26 -0700 Message-ID: <20260321175427.86000-4-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260321175427.86000-1-sj@kernel.org> References: <20260321175427.86000-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 0DD80C0008 X-Stat-Signature: ehr4nwbretjo9fu7id1sxkzn43ju8647 X-Rspam-User: X-HE-Tag: 1774115676-449535 X-HE-Meta: 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 hGzfDWn0 +Av+/ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Josh Law damon_sysfs_repeat_call_fn() calls damon_sysfs_upd_tuned_intervals(), damon_sysfs_upd_schemes_stats(), and damon_sysfs_upd_schemes_effective_quotas() without checking contexts->nr. If nr_contexts is set to 0 via sysfs while DAMON is running, these functions dereference contexts_arr[0] and cause a NULL pointer dereference. Add the missing check. For example, the issue can be reproduced using DAMON sysfs interface and DAMON user-space tool (damo) [1] like below. $ sudo damo start --refresh_interval 1s $ echo 0 | sudo tee \ /sys/kernel/mm/damon/admin/kdamonds/0/contexts/nr_contexts [1] https://github.com/damonitor/damo Link: https://patch.msgid.link/20260320163559.178101-3-objecting@objecting.org Fixes: d809a7c64ba8 ("mm/damon/sysfs: implement refresh_ms file internal work") Cc: # 6.17.x Signed-off-by: Josh Law Reviewed-by: SeongJae Park Signed-off-by: SeongJae Park --- mm/damon/sysfs.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c index ddc30586c0e61..6a44a2f3d8fc9 100644 --- a/mm/damon/sysfs.c +++ b/mm/damon/sysfs.c @@ -1620,9 +1620,12 @@ static int damon_sysfs_repeat_call_fn(void *data) if (!mutex_trylock(&damon_sysfs_lock)) return 0; + if (sysfs_kdamond->contexts->nr != 1) + goto out; damon_sysfs_upd_tuned_intervals(sysfs_kdamond); damon_sysfs_upd_schemes_stats(sysfs_kdamond); damon_sysfs_upd_schemes_effective_quotas(sysfs_kdamond); +out: mutex_unlock(&damon_sysfs_lock); return 0; } -- 2.47.3