linux-kernel - Re: [PATCH][next] io_uring: Fix incorrect sizeof operator for copy_from

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Date:   Tue, 15 Jun 2021 12:35:52 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Pavel Begunkov <asml.silence@...il.com>,
        Jens Axboe <axboe@...nel.dk>, io-uring@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] io_uring: Fix incorrect sizeof operator for
 copy_from_user call

On 15/06/2021 12:30, Pavel Begunkov wrote:
> On 6/15/21 11:47 AM, Colin Ian King wrote:
>> On 15/06/2021 11:45, Colin King wrote:
>>> From: Colin Ian King <colin.king@...onical.com>
>>>
>>> Static analysis is warning that the sizeof being used is should be
>>> of *data->tags[i] and not data->tags[i]. Although these are the same
>>> size on 64 bit systems it is not a portable assumption to assume
>>> this is true for all cases.
>>>
>>> Addresses-Coverity: ("Sizeof not portable")
>>> Fixes: d878c81610e1 ("io_uring: hide rsrc tag copy into generic helpers")
>>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>>> ---
>>>  fs/io_uring.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>> index d665c9419ad3..6b1a70449749 100644
>>> --- a/fs/io_uring.c
>>> +++ b/fs/io_uring.c
>>> @@ -7231,7 +7231,7 @@ static int io_rsrc_data_alloc(struct io_ring_ctx *ctx, rsrc_put_fn *do_put,
>>>  		ret = -EFAULT;
>>>  		for (i = 0; i < nr; i++) {
>>>  			if (copy_from_user(io_get_tag_slot(data, i), &utags[i],
>>> -					   sizeof(data->tags[i])))
>>> +					   sizeof(*data->tags[i])))
>>>  				goto fail;
>>>  		}
>>>  	}
>>>
> 


> Yep, thanks Colin. I think `sizeof(io_get_tag_slot(data, i))`
> would be less confusing. Or
> 
> u64 *tag_slot = io_get_tag_slot(data, i);
> copy_from_user(tag_slot, ..., sizeof(*tag_slot));
> 
BTW, Coverity is complaining about:

7220                return -ENOMEM;

Wrong sizeof argument (SIZEOF_MISMATCH)

suspicious_sizeof: Passing argument nr * 8UL /* sizeof
(data->tags[0][0]) */ to function io_alloc_page_table and then casting
the return value to u64 ** is suspicious.

7221        data->tags = (u64 **)io_alloc_page_table(nr *
sizeof(data->tags[0][0]));

Not sure if that's a false positive or not. This kind of indirection
makes my brain melt.

Colin