mm-damon-sysfs-check-contexts-nr-before-accessing-contexts_arr.patch removed from -mm tree

The quilt patch titled

     Subject: mm/damon/sysfs: check contexts->nr before accessing contexts_arr[0]

has been removed from the -mm tree. Its filename was
mm-damon-sysfs-check-contexts-nr-before-accessing-contexts_arr.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Josh Law <[email protected]>
Subject: mm/damon/sysfs: check contexts->nr before accessing contexts_arr[0]
Date: Sat, 21 Mar 2026 10:54:25 -0700

Multiple sysfs command paths dereference contexts_arr[0] without first verifying that kdamond->contexts->nr == 1. A user can set nr_contexts to 0 via sysfs while DAMON is running, causing NULL pointer dereferences.

In more detail, the issue can be triggered by privileged users like below.

First, start DAMON and make contexts directory empty (kdamond->contexts->nr == 0).

    # damo start
    # cd /sys/kernel/mm/damon/admin/kdamonds/0
    # echo 0 > contexts/nr_contexts

Then, each of below commands will cause the NULL pointer dereference.

    # echo update_schemes_stats > state
    # echo update_schemes_tried_regions > state
    # echo update_schemes_tried_bytes > state
    # echo update_schemes_effective_quotas > state
    # echo update_tuned_intervals > state

Guard all commands (except OFF) at the entry point of damon_sysfs_handle_cmd().

---

 mm/damon/sysfs.c |    3 +++
 1 file changed, 3 insertions(+)

@@ -1749,6 +1749,9 @@ static int damon_sysfs_update_schemes_tr
 static int damon_sysfs_handle_cmd(enum damon_sysfs_cmd cmd,
 		struct damon_sysfs_kdamond *kdamond)
 {
+	if (cmd != DAMON_SYSFS_CMD_OFF && kdamond->contexts->nr != 1)
+		return -EINVAL;
+
 	switch (cmd) {
 	case DAMON_SYSFS_CMD_ON:
 		return damon_sysfs_turn_damon_on(kdamond);

_

Patches currently in -mm which might be from [email protected] are

mm-damon-core-document-damos_commit_dests-failure-semantics.patch lib-maple_tree-fix-swapped-arguments-in-mas_safe_pivot-call.patch lib-glob-fix-grammar-and-replace-non-inclusive-terminology.patch lib-glob-add-explicit-include-for-exporth.patch lib-glob-replace-bitwise-or-with-logical-operation-on-boolean.patch lib-glob-clean-up-bool-abuse-in-pointer-arithmetic.patch lib-uuid-fix-typo-reversion-to-revision-in-comment.patch lib-inflate-fix-memory-leak-in-inflate_fixed-on-inflate_codes-failure.patch lib-inflate-fix-memory-leak-in-inflate_dynamic-on-inflate_codes-failure.patch lib-inflate-fix-grammar-in-comment-variable-to-variables.patch lib-inflate-fix-typo-this-results-to-the-results-in-comment.patch lib-bug-fix-inconsistent-capitalization-in-bug-message.patch lib-bug-remove-unnecessary-variable-initializations.patch lib-decompress_bunzip2-fix-32-bit-shift-undefined-behavior.patch lib-ts_bm-fix-integer-overflow-in-pattern-length-calculation.patch lib-ts_kmp-fix-integer-overflow-in-pattern-length-calculation.patch lib-glob-initialize-back_str-to-silence-uninitialized-variable-warning.patch lib-bch-fix-signed-left-shift-undefined-behavior.patch lib-bch-fix-signed-shift-overflow-in-build_mod8_tables.patch lib-idr-fix-ida_find_first_range-missing-ids-across-chunk-boundaries.patch