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 bb41715..83b1e8c 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -1187,7 +1187,22 @@
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;
}
/*