linux-kernel - [PATCH] libfs: fix negative value support in simple_attr

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Date:   Sun, 18 Sep 2022 13:50:36 +0000
From:   Eliav Farber <farbere@...zon.com>
To:     <viro@...iv.linux.org.uk>, <akpm@...ux-foundation.org>,
        <yangyicong@...ilicon.com>, <linux-fsdevel@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <andriy.shevchenko@...el.com>, <farbere@...zon.com>,
        <hhhawa@...zon.com>, <jonnyc@...zon.com>
Subject: [PATCH] libfs: fix negative value support in simple_attr_write()

After commit 488dac0c9237 ("libfs: fix error cast of negative value in
simple_attr_write()"), a user trying set a negative value will get a
'-EINVAL' error, because simple_attr_write() was modified to use
kstrtoull() which can handle only unsigned values, instead of
simple_strtoll().

This breaks all the places using DEFINE_DEBUGFS_ATTRIBUTE() with format
of a signed integer.

The u64 value which attr->set() receives is not an issue for negative
numbers.
The %lld and %llu in any case are for 64-bit value. Representing it as
unsigned simplifies the generic code, but it doesn't mean we can't keep
their signed value if we know that.

This change basically reverts the mentioned commit, but uses kstrtoll()
instead of simple_strtoll() which is obsolete.

Fixes: 488dac0c9237 ("libfs: fix error cast of negative value in simple_attr_write()")
Signed-off-by: Eliav Farber <farbere@...zon.com>
---
 fs/libfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/libfs.c b/fs/libfs.c
index 31b0ddf01c31..3bccd75815db 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -1016,7 +1016,7 @@ 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);
+	ret = kstrtoll(attr->set_buf, 0, &val);
 	if (ret)
 		goto out;
 	ret = attr->set(attr->data, val);
-- 
2.37.1