[PATCH] libfs: fix error cast of negative value in simple_attr_write()

[Yicong Yang]

The attr->set() receive a value of u64, but we use simple_strtoll()
for doing the conversion. It will lead to the error cast if user inputs
a negative value.

Use kstrtoull() instead to resolve this issue, -EINVAL will be returned
if a negative value is input.

Fixes: f7b88631a897 ("fs/libfs.c: fix simple_attr_write() on 32bit machines")
Signed-off-by: Yicong Yang <yangyicong@xxxxxxxxxxxxx>
---
 fs/libfs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/libfs.c b/fs/libfs.c
index e0d42e9..803c439 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -975,7 +975,9 @@ 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 */
--
2.8.1