xfs: ensure post-EOF zeroing happens after zeroing part of a file

If a user asks us to zero_range part of a file, the end of the range is
EOF, and not aligned to a page boundary, invoke writeback of the EOF
page to ensure that the post-EOF part of the page is zeroed.  This
ensures that we don't expose stale memory contents via mmap, if in a
clumsy manner.

Found by running generic/127 when it runs zero_range and mapread at EOF
one after the other.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>

diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index bb417156e3bf74f3d9f6b1e315598ffe7890e9b9..83b1e8c6c18f939e8afcabdb4eb37fd33e459da8 100644 (file)
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -1187,7 +1187,22 @@ xfs_free_file_space(
                return 0;
        if (offset + len > XFS_ISIZE(ip))
                len = XFS_ISIZE(ip) - offset;
-       return iomap_zero_range(VFS_I(ip), offset, len, NULL, &xfs_iomap_ops);
+       error = iomap_zero_range(VFS_I(ip), offset, len, NULL, &xfs_iomap_ops);
+       if (error)
+               return error;
+
+       /*
+        * If we zeroed right up to EOF and EOF straddles a page boundary we
+        * must make sure that the post-EOF area is also zeroed because the
+        * page could be mmap'd and iomap_zero_range doesn't do that for us.
+        * Writeback of the eof page will do this, albeit clumsily.
+        */
+       if (offset + len >= XFS_ISIZE(ip) && ((offset + len) & PAGE_MASK)) {
+               error = filemap_write_and_wait_range(VFS_I(ip)->i_mapping,
+                               (offset + len) & ~PAGE_MASK, LLONG_MAX);
+       }
+
+       return error;
 }
 
 /*