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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Tejun Heo <tj@kernel.org>,
        Ivan Vecera <ivecera@redhat.com>,
        Al Viro <viro@zeniv.linux.org.uk>
Subject: [PATCH 4.9 27/88] kernfs: fix regression in kernfs_fop_write caused by wrong type
Date:   Thu, 15 Feb 2018 16:16:54 +0100
Message-Id: <20180215151226.418654572@linuxfoundation.org>
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4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ivan Vecera <ivecera@redhat.com>

commit ba87977a49913129962af8ac35b0e13e0fa4382d upstream.

Commit b7ce40cff0b9 ("kernfs: cache atomic_write_len in
kernfs_open_file") changes type of local variable 'len' from ssize_t
to size_t. This change caused that the *ppos value is updated also
when the previous write callback failed.

Mentioned snippet:
...
len = ops->write(...); <- return value can be negative
...
if (len > 0)           <- true here in this case
        *ppos += len;
...

Fixes: b7ce40cff0b9 ("kernfs: cache atomic_write_len in kernfs_open_file")
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/kernfs/file.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -275,7 +275,7 @@ static ssize_t kernfs_fop_write(struct f
 {
 	struct kernfs_open_file *of = kernfs_of(file);
 	const struct kernfs_ops *ops;
-	size_t len;
+	ssize_t len;
 	char *buf;
 
 	if (of->atomic_write_len) {