[patch 7/8] libfs: fix error cast of negative value in simple_attr_write()

[Andrew Morton <akpm@linux-foundation.org>]

From: Yicong Yang <yangyicong@hisilicon.com>
Subject: libfs: fix error cast of negative value in simple_attr_write()

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.  Make 'val' unsigned long long as what kstrtoull() takes, this
will eliminate the compile warning on no 64-bit architectures.

Link: https://lkml.kernel.org/r/1605341356-11872-1-git-send-email-yangyicong@hisilicon.com
Fixes: f7b88631a897 ("fs/libfs.c: fix simple_attr_write() on 32bit machines")
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/libfs.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/fs/libfs.c~libfs-fix-error-cast-of-negative-value-in-simple_attr_write
+++ a/fs/libfs.c
@@ -959,7 +959,7 @@ ssize_t simple_attr_write(struct file *f
 			  size_t len, loff_t *ppos)
 {
 	struct simple_attr *attr;
-	u64 val;
+	unsigned long long val;
 	size_t size;
 	ssize_t ret;
 
@@ -977,7 +977,9 @@ ssize_t simple_attr_write(struct file *f
 		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 */
_