[PATCH][next] io_uring: Fix incorrect sizeof operator for copy_from_user call

[PATCH][next] io_uring: Fix incorrect sizeof operator for copy_from_user call

[Colin King]

From: Colin Ian King <colin.king@canonical.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@canonical.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;
 		}
 	}
-- 
2.31.1

Re: [PATCH][next] io_uring: Fix incorrect sizeof operator for copy_from_user call

[Colin Ian King]

On 15/06/2021 11:45, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.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@canonical.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;
>  		}
>  	}
> 

Actually, I think there is also an issue on line 7220 too, I'll fix that
and re-send.

Re: [PATCH][next] io_uring: Fix incorrect sizeof operator for copy_from_user call

[Pavel Begunkov]

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@canonical.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@canonical.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));

-- 
Pavel Begunkov

Re: [PATCH][next] io_uring: Fix incorrect sizeof operator for copy_from_user call

[Colin Ian King]

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@canonical.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@canonical.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

Re: [PATCH][next] io_uring: Fix incorrect sizeof operator for copy_from_user call

[Pavel Begunkov]

On 6/15/21 12:35 PM, Colin Ian King wrote:
> 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@canonical.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@canonical.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]));

Ah, this one. We want it to be indexed linearly, but can't allocate
as much, so together with io_get_tag_slot() it hides two level
tables from us, providing linear indexing.

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

So, this one should be a false positive. But agree about the
indirection, it's not the first sizeof bug you found. Any
better ideas how to push it to the type system?

I think something like below would make more sense

#define copy_from_user_typed(from, to) \
    assert(typeof(from) == typeof(to)),
    copy_from_user(from, to, sizeof(*from));

-- 
Pavel Begunkov