On Tue, Aug 23, 2016 at 03:05:42PM -0400, Doug Ledford wrote: > On 8/23/2016 3:00 PM, Shiraz Saleem wrote: > > On Tue, Aug 23, 2016 at 09:46:23PM +0300, Leon Romanovsky wrote: > >> On Tue, Aug 23, 2016 at 12:51:10PM -0400, Doug Ledford wrote: > >>> On 8/23/2016 12:00 PM, Shiraz Saleem wrote: > >>>> On Tue, Aug 23, 2016 at 04:41:35AM +0300, Leon Romanovsky wrote: > >>>>> On Mon, Aug 22, 2016 at 07:01:47PM -0500, Shiraz Saleem wrote: > >>>>>> From: Mustafa Ismail <mustafa.ismail@xxxxxxxxx> > >>>>>> > >>>>>> In i40iw_free_virt_mem(), do not set mem->va to NULL > >>>>>> after freeing it as mem->va is a self-referencing pointer > >>>>>> to mem. > >>>>> > >>>>> Sorry, I failed to understand your commit message and your change. > >>>>> What did you mean? How do you suppose to use mem->va pointer > >>>>> after kfree() call on that pointer? Won't you have use-after-free bug in > >>>>> such case? > >>>> > >>>> The pointer mem->va cannot be used after kfree. But setting it to > >>>> NULL would be writing to freed memory. In i40iw_puda_alloc_buf(), > >>>> when a buffer is allocated of type struct i40iw_puda_buf, the address > >>>> of the buffer itself is stored within the structure (in member buf_mem). > >>>> When this pointer is freed, the structure containing the pointer is freed, > >>>> so writing to the structure would be writing to freed memory, which is > >>>> what this fix is for. > >>>> > >>>>>> > >>>>>> Fixes: 4e9042e647ff ("i40iw: add hw and utils files") > >>>>>> > >>>>>> Reported-by: Stefan Assmann <sassmann@xxxxxxxxxx> > >>>>>> Signed-off-by: Mustafa Ismail <mustafa.ismail@xxxxxxxxx> > >>>>>> Signed-off-by: Shiraz Saleem <shiraz.saleem@xxxxxxxxx> > >>>>>> --- > >>>>>> > >>>>>> V2: Fix typo in subject line. > >>>>>> > >>>>>> drivers/infiniband/hw/i40iw/i40iw_utils.c | 1 - > >>>>>> 1 file changed, 1 deletion(-) > >>>>>> > >>>>>> diff --git a/drivers/infiniband/hw/i40iw/i40iw_utils.c b/drivers/infiniband/hw/i40iw/i40iw_utils.c > >>>>>> index 0e8db0a..d5f5de2 100644 > >>>>>> --- a/drivers/infiniband/hw/i40iw/i40iw_utils.c > >>>>>> +++ b/drivers/infiniband/hw/i40iw/i40iw_utils.c > >>>>>> @@ -674,7 +674,6 @@ enum i40iw_status_code i40iw_free_virt_mem(struct i40iw_hw *hw, > >>>>>> if (!mem) > >>>>>> return I40IW_ERR_PARAM; > >>>>>> kfree(mem->va); > >>>>>> - mem->va = NULL; > >>>>>> return 0; > >>> > >>> Your commit message is a bit hard to follow, but if I follow the > >>> conversation, kfree(mem->va) is the same as kfree(mem), is it not? If > >>> it is, couldn't you just kfree(mem)? That would avoid the confusion > >>> here. Also, if it matters, you can use a temporary pointer, aka: > >>> > >>> p = mem->va; > >>> mem->va = NULL; > >>> kfree(p); > >>> > >>> but, again, if mem->va is just a self-referencing pointer back to mem, > >>> then why not just kfree(mem)? I'm concerned that this convoluted way of > >>> doing things will come back to haunt us later when people think they are > >>> submitting a fix and simply reintroduce the same bug again. > >> > >> Yeah, I totally agree with you. > >> > > > > OK, I see the the possible confusion of the commit message. > > > > Maybe the following is clearer: > > "In i40iw_free_virt_mem(), do not set mem->va to NULL after freeing it, as mem->va is a pointer > > to the structure containing mem" > > > > So kfree(mem->va) is not the same as kfree(mem). > > That makes more sense. I still think things are a bit convoluted here, > and maybe even a code comment is in order. I'll probably change it up a > little bit as I pull it in. I would like to see code snippet of such struct and/or code which is depend on it. Thanks > > > -- > Doug Ledford <dledford@xxxxxxxxxx> > GPG Key ID: 0E572FDD >
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