The patch titled Subject: mm/damon/sysfs: fix use-after-free in state_show() has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-damon-sysfs-fix-use-after-free-in-state_show.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Stanislav Fort stanislav.fort@aisle.com Subject: mm/damon/sysfs: fix use-after-free in state_show() Date: Fri, 5 Sep 2025 13:10:46 +0300

state_show() reads kdamond->damon_ctx without holding damon_sysfs_lock. This allows a use-after-free race:

CPU 0 CPU 1 ----- ----- state_show() damon_sysfs_turn_damon_on() ctx = kdamond->damon_ctx; mutex_lock(&damon_sysfs_lock); damon_destroy_ctx(kdamond->damon_ctx); kdamond->damon_ctx = NULL; mutex_unlock(&damon_sysfs_lock); damon_is_running(ctx); /* ctx is freed */ mutex_lock(&ctx->kdamond_lock); /* UAF */

(The race can also occur with damon_sysfs_kdamonds_rm_dirs() and damon_sysfs_kdamond_release(), which free or replace the context under damon_sysfs_lock.)

Fix by taking damon_sysfs_lock before dereferencing the context, mirroring the locking used in pid_show().

The bug has existed since state_show() first accessed kdamond->damon_ctx.

Link: https://lkml.kernel.org/r/20250905101046.2288-1-disclosure@aisle.com Fixes: a61ea561c871 ("mm/damon/sysfs: link DAMON for virtual address spaces monitoring") Signed-off-by: Stanislav Fort disclosure@aisle.com Reported-by: Stanislav Fort disclosure@aisle.com Reviewed-by: SeongJae Park sj@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/damon/sysfs.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-)

--- a/mm/damon/sysfs.c~mm-damon-sysfs-fix-use-after-free-in-state_show +++ a/mm/damon/sysfs.c @@ -1260,14 +1260,18 @@ static ssize_t state_show(struct kobject { struct damon_sysfs_kdamond *kdamond = container_of(kobj, struct damon_sysfs_kdamond, kobj); - struct damon_ctx *ctx = kdamond->damon_ctx; - bool running; + struct damon_ctx *ctx; + bool running = false;

- if (!ctx) - running = false; - else + if (!mutex_trylock(&damon_sysfs_lock)) + return -EBUSY; + + ctx = kdamond->damon_ctx; + if (ctx) running = damon_is_running(ctx);

+ mutex_unlock(&damon_sysfs_lock); + return sysfs_emit(buf, "%s\n", running ? damon_sysfs_cmd_strs[DAMON_SYSFS_CMD_ON] : damon_sysfs_cmd_strs[DAMON_SYSFS_CMD_OFF]); _

Patches currently in -mm which might be from stanislav.fort@aisle.com are

mm-damon-sysfs-fix-use-after-free-in-state_show.patch