kernfs: fix regression in kernfs_fop_write caused by wrong type

Web:        https://git.kernel.org/torvalds/c/ba87977a49913129962af8ac35b0e13e0fa4382d
Commit:     ba87977a49913129962af8ac35b0e13e0fa4382d
Parent:     ce4bb04cae8924792ed92f4af2793b77fc986f0e
Refname:    refs/heads/master
Author:     Ivan Vecera <[email protected]>
AuthorDate: Fri Jan 19 09:18:54 2018 +0100
Committer:  Al Viro <[email protected]>
CommitDate: Fri Jan 19 12:19:13 2018 -0500

    kernfs: fix regression in kernfs_fop_write caused by wrong type
    
    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 <[email protected]>
    Signed-off-by: Ivan Vecera <[email protected]>
    Signed-off-by: Al Viro <[email protected]>
---
 fs/kernfs/file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 9698e51656b1..d8f49c412f50 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -275,7 +275,7 @@ static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf,
 {
 	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) {
--
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