Re: Re: [PATCH v2] rdma/siw: Fix a use after free in siw_alloc_mr

[lyl2019@mail.ustc.edu.cn]

> -----原始邮件-----
> 发件人: "Leon Romanovsky" <leon@kernel.org>
> 发送时间: 2021-04-26 13:08:50 (星期一)
> 收件人: "Lv Yunlong" <lyl2019@mail.ustc.edu.cn>
> 抄送: bmt@zurich.ibm.com, dledford@redhat.com, jgg@ziepe.ca, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org
> 主题: 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@mail.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
> > 
> > 

Yes, i would like to share some details about it although it still has no name.
We designed this analzyer by adopt a deep learning model to recognize the
memory allocation and deallocation in kernel first. And then use Clang Static
Analyzer to scan the kernel code.