linux-kernel - Re: [PATCH v2] RDMA/rxe: Prevent from double freeing rxe_map

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Date:   Tue, 4 Jan 2022 20:44:34 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Li Zhijian <lizhijian@...fujitsu.com>
Cc:     zyjzyj2000@...il.com, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org, yanjun.zhu@...ux.dev,
        rpearsonhpe@...il.com
Subject: Re: [PATCH v2] RDMA/rxe: Prevent from double freeing rxe_map_set

On Tue, Dec 28, 2021 at 09:44:06AM +0800, Li Zhijian wrote:
> a same rxe_map_set could be freed twice:
> rxe_reg_user_mr()
>   -> rxe_mr_init_user()
>     -> rxe_mr_free_map_set() # 1st
>   -> rxe_drop_ref()
>    ...
>     -> rxe_mr_cleanup()
>       -> rxe_mr_free_map_set() # 2nd
> 
> By convention, we should cleanup/free resources in the error path in the
> same function where the resources are alloted in. So rxe_mr_init_user()
> doesn't need to free the map_set directly.
> 
> In addition, we have to reset map_set to NULL inside rxe_mr_alloc() if needed
> to prevent from map_set being double freed in rxe_mr_cleanup().
> 
> CC: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Li Zhijian <lizhijian@...fujitsu.com>
> Acked-by: Zhu Yanjun <zyjzyj2000@...il.com>
> ---
> V2: Fix it by a simpler way by following suggestion from Bob,
> ---
>  drivers/infiniband/sw/rxe/rxe_mr.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)

Applied to for-rc, but I changed it to keep the goto unwind as is
normal.

@@ -135,19 +135,19 @@ static int rxe_mr_alloc(struct rxe_mr *mr, int num_buf, int both)
 
        ret = rxe_mr_alloc_map_set(num_map, &mr->cur_map_set);
        if (ret)
-               goto err_out;
+               return -ENOMEM;
 
        if (both) {
                ret = rxe_mr_alloc_map_set(num_map, &mr->next_map_set);
-               if (ret) {
-                       rxe_mr_free_map_set(mr->num_map, mr->cur_map_set);
-                       goto err_out;
-               }
+               if (ret)
+                       goto err_free;
        }
 
        return 0;
 
-err_out:
+err_free:
+       rxe_mr_free_map_set(mr->num_map, mr->cur_map_set);
+       mr->cur_map_set = NULL;
        return -ENOMEM;
 }