Re: [PATCH 3/4] blk-cgroup: Add NULL check of pd_alloc_fn in blkcg_activate_policy

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Hi, Tejun

在 2022/10/11 4:29, Tejun Heo 写道:
On Mon, Oct 10, 2022 at 10:38:58AM +0800, Kemeng Shi wrote:
Function only make sure pd_alloc_fn and pd_free_fn in
pairs, so pd_alloc_fn could be NULL in registered blkcg_policy. Check NULL
before use for pd_alloc_fn in blkcg_activate_policy to avoid protential
NULL dereference.

Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxx>
---
  block/blk-cgroup.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 463c568d3e86..fc083c35dc42 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1404,6 +1404,9 @@ int blkcg_activate_policy(struct request_queue *q,
  	if (blkcg_policy_enabled(q, pol))
  		return 0;
+ if (pol->pd_alloc_fn == NULL)
+		return -EINVAL;

This isn't the only place this function is called, so the above won't
achieve much. Given that this is rather trivially noticeable and all the
current users do implement pd_alloc_fn, I'm not sure we need to update this
now.

It's right all the current users implement pd_alloc_fn, can we check
pd_alloc/free_fn NULL instead in blkcg_policy_register()?

Thanks,
Kuai

Thanks.





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