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Commit 31339acd authored by Chris Mason's avatar Chris Mason
Browse files

Btrfs: deal with short returns from copy_from_user 



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: default avatarChris Mason <chris.mason@oracle.com>
cc: stable@kernel.org
parent b1bf862e

fs/btrfs/file.c

+13 −0
Original line number Original line Diff line number Diff line
@@ -69,6 +69,19 @@ static noinline int btrfs_copy_from_user(loff_t pos, int num_pages, 




		/* Flush processor's dcache for this page */

		/* Flush processor's dcache for this page */

		flush_dcache_page(page);

		flush_dcache_page(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);

		iov_iter_advance(i, copied);

		write_bytes -= copied;

		write_bytes -= copied;

		total_copied += copied;

		total_copied += copied;