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Thu, 19 Mar 2026 16:57:46 +0100 (CET) From: Josh Law To: sj@kernel.org, akpm@linux-foundation.org Cc: damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Josh Law Subject: [PATCH 4/4] mm/damon/sysfs: check contexts->nr in repeat_call_fn Date: Thu, 19 Mar 2026 15:57:42 +0000 Message-Id: <20260319155742.186627-5-objecting@objecting.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260319155742.186627-1-objecting@objecting.org> References: <20260319155742.186627-1-objecting@objecting.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-ZohoMailClient: External X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 09A691C0010 X-Stat-Signature: 9nqkonfnxgertgbgnyugmatwc6e8rgmu X-Rspam-User: X-HE-Tag: 1773935878-795973 X-HE-Meta: U2FsdGVkX196jMO7s6un/Di4mTs5GjjbemAfeFAAb1Q8R5RYl7JRX7/h8O1IYXblZ5ImMhfk1TGM1+1W1aGtx8QNyChZ5qVrw+nHO68hJQQ2bCGHk6DGmMwrh9+kimf6MuY2CnbUukgRgVvPLTHs3J/2uwgrzxh50nLeb+4bADIMopUnUzLVbJ3mmzCMB6DFaEYym9fh41YSpqTvi0vsu4f1iUiayCJXpfVlXjlFgsYUt0GOis85va1RBzF8N4WSAXaRkMkeLomuvhDXjxg7NuLDx3xkwjHmTrh/ceagrLeqjln0J3cBfO2Pf7AMKVHbeifCUEH6AlZHP2TUZ4nS+d8e2wi0kKULirt7IP3o7sUt5brdfXBqM3jV4S5MjX81S+BorSqDNBp/3bJnBC4AcV8uYrB3cidYq3QDd5eucL6QAIP9aIrmIe7InAquz8AwG6qYCvck8IiT48y6RIHj9pu25P8it/yRv1qf61qfxojxp2IpJBHZYZX6vVTv3ErvG4b4bZSJEkA1xrRNnVf3oKxTbpd1h/q7Uek0kRCqEpzaGraORL5OzZXfrUvsKY7PxbdPocrK8Wo5Un0hOIDufOW7qlBW+lWpQztH3K5B+qatomeMwhjDxSM1wt3PDhBWHEgpbyMFBECKd/KSNh66bAnbKHk2mhGDUpGPWScA6dmCwlfzS5huUPjSyv7NjeDx7o3SsS6NR5ViWWCKfXCEASO/Cu+Q4RMvX2TM83MthNhuCMmOmrWWt3ZYZr9G7eJSWK+xjTgohEXpiPL4G/YQmaXJAyqjGQLtCr7+oyZeWv8KSOYWId3UzjESI3dsuphD0JLVufHWhRhZMEmqn/q3UwUq571r2OScm3fQqL27tIeTNfr/Em+6yAUuciCgYKehwdK0s2o81EOf3i8zKBKBUgzp3hrdfZ3MOv4isLRNY0KMzw0iLybd4PXJ8xNIkZyuYwEQwGGdrnhCxEGw4tk CwKb1p5j xkq43H+tPyn4JAHE244TvCI7lZ1U2V+CqWutC8EOWUelIZW4JbOIwP5B+KQrflxZMAhkZcyiktBZ9jdnAf/bKGELbdoWu344my6FPF/LksE2q3s02PxaRe9kiH6t7w8ofuoJJ8yScnae6qTt3miKxrCMjEa0Y1/d+7SNcWBK9t2XgIhMQTmi/GU5SeDJpQckHxdOKyvumXhx95wAbpZ3tnyfSBLswPbBbvxv7kTSzYlzlANq6cbLeYpVNCEpw2hDJLRmo37+RWPZ1EnESW86CCJQxAyYOXwkZvxmclMKekjR4O5qYj/u65Mmhvj7vFUNPsNJpKJsBmmXCjWA7MQEBS5qj4QsgJ0nCPFj5QqXYll1gqRH0epELihMi3xQRLDgyJvLNIhUzXl9no/7/2M09XHZTej1STOl9Zv9iNYCJ/2dFJCw= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: damon_sysfs_repeat_call_fn() accesses contexts_arr[0] in upd_tuned_intervals, upd_schemes_stats, and upd_schemes_effective_quotas without checking nr_contexts. A user can set nr_contexts to 0 via sysfs while DAMON is running, causing a NULL pointer dereference in the repeat callback. Add a guard under the lock. Signed-off-by: Josh Law --- mm/damon/sysfs.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c index ddcdc4e35b27..d982f2dc7a2b 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; } -- 2.34.1