From: Hou Tao Date: Mon, 19 Sep 2022 14:48:11 +0000 (+0800) Subject: bpf: Check whether or not node is NULL before free it in free_bulk X-Git-Tag: v6.6.17~6504^2~10^2~44 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=c31b38cb948ee7d3317139f005fa1f90de4a06b7;p=platform%2Fkernel%2Flinux-rpi.git bpf: Check whether or not node is NULL before free it in free_bulk llnode could be NULL if there are new allocations after the checking of c-free_cnt > c->high_watermark in bpf_mem_refill() and before the calling of __llist_del_first() in free_bulk (e.g. a PREEMPT_RT kernel or allocation in NMI context). And it will incur oops as shown below: BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] PREEMPT_RT SMP CPU: 39 PID: 373 Comm: irq_work/39 Tainted: G W 6.0.0-rc6-rt9+ #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) RIP: 0010:bpf_mem_refill+0x66/0x130 ...... Call Trace: irq_work_single+0x24/0x60 irq_work_run_list+0x24/0x30 run_irq_workd+0x18/0x20 smpboot_thread_fn+0x13f/0x2c0 kthread+0x121/0x140 ? kthread_complete_and_exit+0x20/0x20 ret_from_fork+0x1f/0x30 Simply fixing it by checking whether or not llnode is NULL in free_bulk(). Fixes: 8d5a8011b35d ("bpf: Batch call_rcu callbacks instead of SLAB_TYPESAFE_BY_RCU.") Signed-off-by: Hou Tao Link: https://lore.kernel.org/r/20220919144811.3570825-1-houtao@huaweicloud.com Signed-off-by: Alexei Starovoitov --- diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c index 20621f5..5f83be1 100644 --- a/kernel/bpf/memalloc.c +++ b/kernel/bpf/memalloc.c @@ -277,7 +277,8 @@ static void free_bulk(struct bpf_mem_cache *c) local_dec(&c->active); if (IS_ENABLED(CONFIG_PREEMPT_RT)) local_irq_restore(flags); - enque_to_free(c, llnode); + if (llnode) + enque_to_free(c, llnode); } while (cnt > (c->high_watermark + c->low_watermark) / 2); /* and drain free_llist_extra */