Fix a race where irq_work can be queued in bpf_ringbuf_commit()
but the ring buffer is freed before the work executes.
In the syzbot reproducer, a BPF program attached to sched_switch
triggers bpf_ringbuf_commit(), queuing an irq_work. If the ring buffer
is freed before this work executes, the irq_work thread may accesses
freed memory.
Calling `irq_work_sync(&rb->work)` ensures that all pending irq_work
complete before freeing the buffer

Fixes: 457f44363a88 ("bpf: Implement BPF ring buffer and verifier support for it")
Reported-by: syzbot+2617fc732430968b45d2@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=2617fc732430968b45d2
Tested-by: syzbot+2617fc732430968b45d2@syzkaller.appspotmail.com
Signed-off-by: Noorain Eqbal <nooraineqbal@gmail.com>
---
v2: Updated the commit message for clarity.
---
 kernel/bpf/ringbuf.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
index 719d73299397..d706c4b7f532 100644
--- a/kernel/bpf/ringbuf.c
+++ b/kernel/bpf/ringbuf.c
@@ -216,6 +216,8 @@ static struct bpf_map *ringbuf_map_alloc(union bpf_attr *attr)
 
 static void bpf_ringbuf_free(struct bpf_ringbuf *rb)
 {
+	irq_work_sync(&rb->work);
+
 	/* copy pages pointer and nr_pages to local variable, as we are going
 	 * to unmap rb itself with vunmap() below
 	 */
-- 
2.51.0