If damon_call() is executed against a DAMON context that is not running, the function returns error while keeping the damon_call_control object linked to the context's call_controls list. Let's suppose the object is deallocated after the damon_call(), and yet another damon_call() is executed against the same context. The function tries to add the new damon_call_control object to the call_controls list, which still has the pointer to the previous damon_call_control object, which is deallocated. As a result, use-after-free happens.
This can actually be triggered using the DAMON sysfs interface. It is not easily exploitable since it requires the sysfs write permission and making a definitely weird file writes, though. Please refer to the report for more details about the issue reproduction steps.
Fix the issue by making two changes. Firstly, move the final kdamond_call() for cancelling all existing damon_call() requests from terminating DAMON context to be done before the ctx->kdamond reset. This makes any code that sees NULL ctx->kdamond can safely assume the context may not access damon_call() requests anymore. Secondly, let damon_call() to cleanup the damon_call_control objects that were added to the already-terminated DAMON context, before returning the error.
Fixes: 004ded6bee11 ("mm/damon: accept parallel damon_call() requests") Reported-by: JaeJoon Jung rgbi3307@gmail.com Closes: https://lore.kernel.org/20251224094401.20384-1-rgbi3307@gmail.com Cc: stable@vger.kernel.org # 6.17.x Signed-off-by: SeongJae Park sj@kernel.org --- Changes from v1 (https://lkml.kernel.org/r/20251228183105.289441-1-sj@kernel.org): - Do final kdamond_call() before ctx->kdamond reset. - Fix Fixes: tag.
mm/damon/core.c | 33 +++++++++++++++++++++++++++++++-- 1 file changed, 31 insertions(+), 2 deletions(-)
diff --git a/mm/damon/core.c b/mm/damon/core.c index 2d3e8006db50..199529dd7c66 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -1442,6 +1442,35 @@ bool damon_is_running(struct damon_ctx *ctx) return running; }
+/* + * damon_call_handle_inactive_ctx() - handle DAMON call request that added to + * an inactive context. + * @ctx: The inactive DAMON context. + * @control: Control variable of the call request. + * + * This function is called in a case that @control is added to @ctx but @ctx is + * not running (inactive). See if @ctx handled @control or not, and cleanup + * @control if it was not handled. + * + * Returns 0 if @control was handled by @ctx, negative error code otherwise. + */ +static int damon_call_handle_inactive_ctx( + struct damon_ctx *ctx, struct damon_call_control *control) +{ + struct damon_call_control *c; + + mutex_lock(&ctx->call_controls_lock); + list_for_each_entry(c, &ctx->call_controls, list) { + if (c == control) { + list_del(&control->list); + mutex_unlock(&ctx->call_controls_lock); + return -EINVAL; + } + } + mutex_unlock(&ctx->call_controls_lock); + return 0; +} + /** * damon_call() - Invoke a given function on DAMON worker thread (kdamond). * @ctx: DAMON context to call the function for. @@ -1472,7 +1501,7 @@ int damon_call(struct damon_ctx *ctx, struct damon_call_control *control) list_add_tail(&control->list, &ctx->call_controls); mutex_unlock(&ctx->call_controls_lock); if (!damon_is_running(ctx)) - return -EINVAL; + return damon_call_handle_inactive_ctx(ctx, control); if (control->repeat) return 0; wait_for_completion(&control->completion); @@ -2797,13 +2826,13 @@ static int kdamond_fn(void *data) if (ctx->ops.cleanup) ctx->ops.cleanup(ctx); kfree(ctx->regions_score_histogram); + kdamond_call(ctx, true);
pr_debug("kdamond (%d) finishes\n", current->pid); mutex_lock(&ctx->kdamond_lock); ctx->kdamond = NULL; mutex_unlock(&ctx->kdamond_lock);
- kdamond_call(ctx, true); damos_walk_cancel(ctx);
mutex_lock(&damon_lock);
base-commit: 40fd05d807b3a7678e3284b8a9a6cb89a32fa8ce