Commit 64873307 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by Andrii Nakryiko
Browse files

bpf: Add a recursion check to prevent loops in bpf_timer 



Do not schedule timer/wq operation on a cpu that is in irq_work
callback that is processing async_cmds queue.
Otherwise the following loop is possible:
bpf_timer_start() -> bpf_async_schedule_op() -> irq_work_queue().
irqrestore -> bpf_async_irq_worker() -> tracepoint -> bpf_timer_start().

Fixes: 1bfbc267 ("bpf: Enable bpf_timer and bpf_wq in any context")
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260204055147.54960-4-alexei.starovoitov@gmail.com
parent 67ee5ad2

kernel/bpf/helpers.c

+16 −0
Original line number Diff line number Diff line
@@ -1427,9 +1427,23 @@ static int bpf_async_update_prog_callback(struct bpf_async_cb *cb, 
	return 0;

}



static DEFINE_PER_CPU(struct bpf_async_cb *, async_cb_running);



static int bpf_async_schedule_op(struct bpf_async_cb *cb, enum bpf_async_op op,

				 u64 nsec, u32 timer_mode)

{

	/*

	 * Do not schedule another operation on this cpu if it's in irq_work

	 * callback that is processing async_cmds queue. Otherwise the following

	 * loop is possible:

	 * bpf_timer_start() -> bpf_async_schedule_op() -> irq_work_queue().

	 * irqrestore -> bpf_async_irq_worker() -> tracepoint -> bpf_timer_start().

	 */

	if (this_cpu_read(async_cb_running) == cb) {

		bpf_async_refcount_put(cb);

		return -EDEADLK;

	}



	struct bpf_async_cmd *cmd = kmalloc_nolock(sizeof(*cmd), 0, NUMA_NO_NODE);



	if (!cmd) {
@@ -1628,6 +1642,7 @@ static void bpf_async_irq_worker(struct irq_work *work) 
		return;



	list = llist_reverse_order(list);

	this_cpu_write(async_cb_running, cb);

	llist_for_each_safe(pos, n, list) {

		struct bpf_async_cmd *cmd;
@@ -1635,6 +1650,7 @@ static void bpf_async_irq_worker(struct irq_work *work) 
		bpf_async_process_op(cb, cmd->op, cmd->nsec, cmd->mode);

		kfree_nolock(cmd);

	}

	this_cpu_write(async_cb_running, NULL);

}



static void bpf_async_cancel_and_free(struct bpf_async_kern *async)