[PATCH 1/3] libfs: add DEFINE_SIMPLE_ATTRIBUTE_SIGNED for signed value

[Akinobu Mita]

The simple attribute files do not accept a negative value since the
commit 488dac0c9237 ("libfs: fix error cast of negative value in
simple_attr_write()"), so we have to use a 64-bit value to write a
negative value.

This adds DEFINE_SIMPLE_ATTRIBUTE_SIGNED for a signed value.

Fixes: 488dac0c9237 ("libfs: fix error cast of negative value in simple_attr_write()")
Reported-by: Zhao Gongyi <zhaogongyi@xxxxxxxxxx>
Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx>
---
 fs/libfs.c         | 22 +++++++++++++++++++---
 include/linux/fs.h | 12 ++++++++++--
 2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/fs/libfs.c b/fs/libfs.c
index 31b0ddf01c31..76fb29a103a2 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -994,8 +994,8 @@ ssize_t simple_attr_read(struct file *file, char __user *buf,
 EXPORT_SYMBOL_GPL(simple_attr_read);
 
 /* interpret the buffer as a number to call the set function with */
-ssize_t simple_attr_write(struct file *file, const char __user *buf,
-			  size_t len, loff_t *ppos)
+static ssize_t simple_attr_write_xsigned(struct file *file, const char __user *buf,
+			  size_t len, loff_t *ppos, bool is_signed)
 {
 	struct simple_attr *attr;
 	unsigned long long val;
@@ -1016,7 +1016,10 @@ ssize_t simple_attr_write(struct file *file, const char __user *buf,
 		goto out;
 
 	attr->set_buf[size] = '\0';
-	ret = kstrtoull(attr->set_buf, 0, &val);
+	if (is_signed)
+		ret = kstrtoll(attr->set_buf, 0, &val);
+	else
+		ret = kstrtoull(attr->set_buf, 0, &val);
 	if (ret)
 		goto out;
 	ret = attr->set(attr->data, val);
@@ -1026,8 +1029,21 @@ ssize_t simple_attr_write(struct file *file, const char __user *buf,
 	mutex_unlock(&attr->mutex);
 	return ret;
 }
+
+ssize_t simple_attr_write(struct file *file, const char __user *buf,
+			  size_t len, loff_t *ppos)
+{
+	return simple_attr_write_xsigned(file, buf, len, ppos, false);
+}
 EXPORT_SYMBOL_GPL(simple_attr_write);
 
+ssize_t simple_attr_write_signed(struct file *file, const char __user *buf,
+			  size_t len, loff_t *ppos)
+{
+	return simple_attr_write_xsigned(file, buf, len, ppos, true);
+}
+EXPORT_SYMBOL_GPL(simple_attr_write_signed);
+
 /**
  * generic_fh_to_dentry - generic helper for the fh_to_dentry export operation
  * @sb:		filesystem to do the file handle conversion on
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9eced4cc286e..c79138818922 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3471,7 +3471,7 @@ void simple_transaction_set(struct file *file, size_t n);
  * All attributes contain a text representation of a numeric value
  * that are accessed with the get() and set() functions.
  */
-#define DEFINE_SIMPLE_ATTRIBUTE(__fops, __get, __set, __fmt)		\
+#define DEFINE_SIMPLE_ATTRIBUTE_XSIGNED(__fops, __get, __set, __fmt, __is_signed)	\
 static int __fops ## _open(struct inode *inode, struct file *file)	\
 {									\
 	__simple_attr_check_format(__fmt, 0ull);			\
@@ -3482,10 +3482,16 @@ static const struct file_operations __fops = {				\
 	.open	 = __fops ## _open,					\
 	.release = simple_attr_release,					\
 	.read	 = simple_attr_read,					\
-	.write	 = simple_attr_write,					\
+	.write	 = (__is_signed) ? simple_attr_write_signed : simple_attr_write,	\
 	.llseek	 = generic_file_llseek,					\
 }
 
+#define DEFINE_SIMPLE_ATTRIBUTE(__fops, __get, __set, __fmt)		\
+	DEFINE_SIMPLE_ATTRIBUTE_XSIGNED(__fops, __get, __set, __fmt, false)
+
+#define DEFINE_SIMPLE_ATTRIBUTE_SIGNED(__fops, __get, __set, __fmt)	\
+	DEFINE_SIMPLE_ATTRIBUTE_XSIGNED(__fops, __get, __set, __fmt, true)
+
 static inline __printf(1, 2)
 void __simple_attr_check_format(const char *fmt, ...)
 {
@@ -3500,6 +3506,8 @@ ssize_t simple_attr_read(struct file *file, char __user *buf,
 			 size_t len, loff_t *ppos);
 ssize_t simple_attr_write(struct file *file, const char __user *buf,
 			  size_t len, loff_t *ppos);
+ssize_t simple_attr_write_signed(struct file *file, const char __user *buf,
+				 size_t len, loff_t *ppos);
 
 struct ctl_table;
 int __init list_bdev_fs_names(char *buf, size_t size);
-- 
2.34.1