linux-kernel - [PATCH 3.16 145/410] kernfs: fix regression in kernfs_fop

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Message-ID: <lsq.1528380321.881398804@decadent.org.uk>
Date:   Thu, 07 Jun 2018 15:05:21 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Tejun Heo" <tj@...nel.org>,
        "Ivan Vecera" <ivecera@...hat.com>,
        "Al Viro" <viro@...iv.linux.org.uk>
Subject: [PATCH 3.16 145/410] kernfs: fix regression in kernfs_fop_write
 caused by wrong type

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Ivan Vecera <ivecera@...hat.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@...nel.org>
Signed-off-by: Ivan Vecera <ivecera@...hat.com>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/kernfs/file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -267,7 +267,7 @@ 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) {