Btrfs: deal with short returns from copy_from_user (31339acd) · Commits · 戴 / test

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@oracle.com> cc: stable@kernel.org

fs/btrfs/file.c

+13 −0

Original line number	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_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);
		write_bytes -= copied;
		total_copied += copied;

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