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.

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

diff --git a/fs/libfs.c b/fs/libfs.c
index fc34361c1489e9eaf5e46fbac653a5edd47becb0..7124c2e8df2f5a5f49451ef8d3bb84c7b8712e80 100644 (file)
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -959,7 +959,7 @@ ssize_t simple_attr_write(struct file *file, const char __user *buf,
                          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 *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 */