[11/87] Btrfs: deal with short returns from copy_from_user

From: Greg KH
Date: Mon Mar 21 2011 - 19:53:28 EST

2.6.37-stable review patch. If anyone has any objections, please let us know.


From: Chris Mason <chris.mason@xxxxxxxxxx>

commit 31339acd07b4ba687906702085127895a56eb920 upstream.

When copy_from_user is only able to copy some of the bytes we requested,
we may end up creating a partially up to date page. To avoid garbage in
the page, we need to treat a partial copy as a zero length copy.

This makes the rest of the file_write code drop the page and
retry the whole copy instead of marking the partially up to
date page as dirty.

Signed-off-by: Chris Mason <chris.mason@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

fs/btrfs/file.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -69,6 +69,19 @@ static noinline int btrfs_copy_from_user

/* Flush processor's dcache for this page */
+ /*
+ * if we get a partial write, we can end up with
+ * partially up to date pages. These add
+ * a lot of complexity, so make sure they don't
+ * happen by forcing this copy to be retried.
+ *
+ * The rest of the btrfs_file_write code will fall
+ * back to page at a time copies after we return 0.
+ */
+ if (!PageUptodate(page) && copied < count)
+ copied = 0;
iov_iter_advance(i, copied);
write_bytes -= copied;
total_copied += copied;

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