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SubjectRe: [RESEND PATCH] libfs: fix error cast of negative value in simple_attr_write()
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Hi,

Thanks for reviewing this.


On 2020/11/11 3:18, Andrew Morton wrote:
> On Tue, 10 Nov 2020 17:25:24 +0800 Yicong Yang <yangyicong@hisilicon.com> wrote:
>
>> The attr->set() receive a value of u64, but simple_strtoll() is used
>> for doing the conversion. It will lead to the error cast if user inputs
>> a negative value.
>>
>> Use kstrtoull() instead of simple_strtoll() to convert a string got
>> from the user to an unsigned value. The former will return '-EINVAL' if
>> it gets a negetive value, but the latter can't handle the situation
>> correctly.
>>
>> ...
>>
>> --- a/fs/libfs.c
>> +++ b/fs/libfs.c
>> @@ -977,7 +977,9 @@ ssize_t simple_attr_write(struct file *file, const char __user *buf,
>> goto out;
>>
>> attr->set_buf[size] = '\0';
>> - val = simple_strtoll(attr->set_buf, NULL, 0);
>> + ret = kstrtoull(attr->set_buf, 0, &val);
>> + if (ret)
>> + goto out;
>> ret = attr->set(attr->data, val);
>> if (ret == 0)
>> ret = len; /* on success, claim we got the whole input */
> kstrtoull() takes an `unsigned long long *', but `val' is a u64.
>
> I think this probably works OK on all architectures (ie, no 64-bit
> architectures are using `unsigned long' for u64). But perhaps `val'
> should have type `unsigned long long'?

the attr->set() takes 'val' as u64, so maybe we can stay it unchanged here
if it works well.

Thanks,
Yicong


> .
>

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