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

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