Re: [PATCH] mtd: phram: use div_u64_rem to stop overwrite len in phram_setup

yangerkun
2021-01-25T08:37:54Z

在 2021/1/25 16:28, Miquel Raynal 写道:
> Hi yangerkun,
>
> yangerkun <yangerkun@huawei.com> wrote on Mon, 25 Jan 2021 13:48:32
> +0800:
>
>> Hi,
>>
>> Recheck the patch, and it seems we need check erasesize to prevent DIV/0...
>
> Can you elaborate a little bit?
>
> The do_div() != 0 has been replaced by the 'rem' condition and it seems
> good to me. So please tell me what division by zero you are talking
> about because the beginning of the if condition is "len == 0 ||
> erasesize == 0 || erasesize > len", so it does already take care of
> this situation.

The patch I send show as follow:

--- a/drivers/mtd/devices/phram.c
+++ b/drivers/mtd/devices/phram.c
@@ -222,6 +222,7 @@ static int phram_setup(const char *val)
uint64_t start;
uint64_t len;
uint64_t erasesize = PAGE_SIZE;
+ uint32_t rem;
int i, ret;

if (strnlen(val, sizeof(buf)) >= sizeof(buf))
@@ -263,8 +264,9 @@ static int phram_setup(const char *val)
}
}

+ div_u64_rem(len, (uint32_t)erasesize, &rem);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Once user set erasesize == 0, the div_u64_rem will trigger the
DIV/0...

if (len == 0 || erasesize == 0 || erasesize > len
- || erasesize > UINT_MAX || do_div(len, (uint32_t)erasesize) != 0) {
+ || erasesize > UINT_MAX || rem) {
parse_err("illegal erasesize or len\n");
goto error;
}
--

>
>>
>> Sorry for the mistake. Can you add a fix patch for this?
>
> In any case if the patch turns out to be wrong I'll ask you to either
> send a fix or send a v2 and I'll drop v1.

Okay, I will send the v2. Sorry again for the mistake.

Thanks,
Kun.

>
>> 在 2021/1/4 18:18, Miquel Raynal 写道:
>>> On Wed, 2020-12-30 at 02:17:18 UTC, yangerkun wrote:
>>>> We now support user to set erase page size, and use do_div between len
>>>> and erase size to determine the reasonableness for the erase size.
>>>> However, do_div is a macro and will overwrite the value of len. Which
>>>> results a mtd device with unexcepted size. Fix it by use div_u64_rem.
>>>>
>>>> Fixes: ffad560394de ("mtd: phram: Allow the user to set the erase page size.")
>>>> Signed-off-by: yangerkun <yangerkun@huawei.com>
>>>
>>> Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/next, thanks.
>
> Thanks,
> Miquèl
> .