linux-kernel - Re: [rds-devel] KASAN: null-ptr-deref Read in rds_ib_get

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Date:   Fri, 11 May 2018 06:46:30 -0400
From:   Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:     Yanjun Zhu <yanjun.zhu@...cle.com>
Cc:     DaeRyong Jeong <threeearcat@...il.com>,
        santosh.shilimkar@...cle.com, davem@...emloft.net,
        rds-devel@....oracle.com, kt0755@...il.com,
        linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, byoungyoung@...due.edu
Subject: Re: [rds-devel] KASAN: null-ptr-deref Read in rds_ib_get_mr

On (05/11/18 15:48), Yanjun Zhu wrote:
> diff --git a/net/rds/ib_rdma.c b/net/rds/ib_rdma.c
> index e678699..2228b50 100644
> --- a/net/rds/ib_rdma.c
> +++ b/net/rds/ib_rdma.c
> @@ -539,11 +539,17 @@ void rds_ib_flush_mrs(void)
>    void *rds_ib_get_mr(struct scatterlist *sg, unsigned long nents,
>                                         struct rds_sock *rs, u32 *key_ret)
>    {
> -             struct rds_ib_device *rds_ibdev;
> +             struct rds_ib_device *rds_ibdev = NULL;
>                 struct rds_ib_mr *ibmr = NULL;
> -             struct rds_ib_connection *ic = rs->rs_conn->c_transport_data;
> +             struct rds_ib_connection *ic = NULL;
>                 int ret;
> 
> +             if (rs->rs_bound_addr == 0) {
> +                             ret = -EPERM;
> +                             goto out;
> +             }
> +
> +             ic = rs->rs_conn->c_transport_data;
>                 rds_ibdev = rds_ib_get_device(rs->rs_bound_addr);
>                 if (!rds_ibdev) {
>                                 ret = -ENODEV;
> 
> I made this raw patch. If you can reproduce this bug, please make tests 
> with it.

I dont think this solves the problem, I think it
just changes the timing under which it can still happen. 

what if the rds_remove_bound() in rds_bind() happens after the check
for if (rs->rs_bound_addr == 0) added above by the patch 

I believe you need some type of synchronization (either
through mutex, or some atomic flag in the rs or similar) to make
sure rds_bind() and rds_ib_get_mr() are mutually exclusive.

--Sowmini