linux-kernel - Re: [PATCH v2] rdma/siw: Fix a use after free in siw_alloc

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Message-ID: <YIZK4gb2qytVpMS0@unreal>
Date:   Mon, 26 Apr 2021 08:08:50 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Lv Yunlong <lyl2019@...l.ustc.edu.cn>
Cc:     bmt@...ich.ibm.com, dledford@...hat.com, jgg@...pe.ca,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] rdma/siw: Fix a use after free in siw_alloc_mr

On Sun, Apr 25, 2021 at 06:16:47PM -0700, Lv Yunlong wrote:
> Our code analyzer reported a uaf.

Can you please share more details about this "code analyzer"?

Thanks

> 
> In siw_alloc_mr, it calls siw_mr_add_mem(mr,..). In the implementation
> of siw_mr_add_mem(), mem is assigned to mr->mem and then mem is freed
> via kfree(mem) if xa_alloc_cyclic() failed. Here, mr->mem still point
> to a freed object. After, the execution continue up to the err_out branch
> of siw_alloc_mr, and the freed mr->mem is used in siw_mr_drop_mem(mr).
> 
> My patch moves "mr->mem = mem" behind the if (xa_alloc_cyclic(..)<0) {}
> section, to avoid the uaf.
> 
> Fixes: 2251334dcac9e ("rdma/siw: application buffer management")
> Signed-off-by: Lv Yunlong <lyl2019@...l.ustc.edu.cn>
> ---
>  drivers/infiniband/sw/siw/siw_mem.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/infiniband/sw/siw/siw_mem.c b/drivers/infiniband/sw/siw/siw_mem.c
> index 34a910cf0edb..96b38cfbb513 100644
> --- a/drivers/infiniband/sw/siw/siw_mem.c
> +++ b/drivers/infiniband/sw/siw/siw_mem.c
> @@ -106,8 +106,6 @@ int siw_mr_add_mem(struct siw_mr *mr, struct ib_pd *pd, void *mem_obj,
>  	mem->perms = rights & IWARP_ACCESS_MASK;
>  	kref_init(&mem->ref);
>  
> -	mr->mem = mem;
> -
>  	get_random_bytes(&next, 4);
>  	next &= 0x00ffffff;
>  
> @@ -116,6 +114,8 @@ int siw_mr_add_mem(struct siw_mr *mr, struct ib_pd *pd, void *mem_obj,
>  		kfree(mem);
>  		return -ENOMEM;
>  	}
> +
> +	mr->mem = mem;
>  	/* Set the STag index part */
>  	mem->stag = id << 8;
>  	mr->base_mr.lkey = mr->base_mr.rkey = mem->stag;
> -- 
> 2.25.1
> 
>