[PATCH 4.14 15/28] nilfs2: initialize unused bytes in segment summary blocks

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Ryusuke Konishi <konishi.ryusuke@gmail.com>

commit ef832747a82dfbc22a3702219cc716f449b24e4a upstream.

Syzbot still reports uninit-value in nilfs_add_checksums_on_logs() for
KMSAN enabled kernels after applying commit 7397031622e0 ("nilfs2:
initialize "struct nilfs_binfo_dat"->bi_pad field").

This is because the unused bytes at the end of each block in segment
summaries are not initialized.  So this fixes the issue by padding the
unused bytes with null bytes.

Link: https://lkml.kernel.org/r/20230417173513.12598-1-konishi.ryusuke@gmail.com
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Tested-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Reported-by: syzbot+048585f3f4227bb2b49b@syzkaller.appspotmail.com
  Link: https://syzkaller.appspot.com/bug?extid=048585f3f4227bb2b49b
Cc: Alexander Potapenko <glider@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/nilfs2/segment.c |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -444,6 +444,23 @@ static int nilfs_segctor_reset_segment_b
 	return 0;
 }
 
+/**
+ * nilfs_segctor_zeropad_segsum - zero pad the rest of the segment summary area
+ * @sci: segment constructor object
+ *
+ * nilfs_segctor_zeropad_segsum() zero-fills unallocated space at the end of
+ * the current segment summary block.
+ */
+static void nilfs_segctor_zeropad_segsum(struct nilfs_sc_info *sci)
+{
+	struct nilfs_segsum_pointer *ssp;
+
+	ssp = sci->sc_blk_cnt > 0 ? &sci->sc_binfo_ptr : &sci->sc_finfo_ptr;
+	if (ssp->offset < ssp->bh->b_size)
+		memset(ssp->bh->b_data + ssp->offset, 0,
+		       ssp->bh->b_size - ssp->offset);
+}
+
 static int nilfs_segctor_feed_segment(struct nilfs_sc_info *sci)
 {
 	sci->sc_nblk_this_inc += sci->sc_curseg->sb_sum.nblocks;
@@ -452,6 +469,7 @@ static int nilfs_segctor_feed_segment(st
 				* The current segment is filled up
 				* (internal code)
 				*/
+	nilfs_segctor_zeropad_segsum(sci);
 	sci->sc_curseg = NILFS_NEXT_SEGBUF(sci->sc_curseg);
 	return nilfs_segctor_reset_segment_buffer(sci);
 }
@@ -556,6 +574,7 @@ static int nilfs_segctor_add_file_block(
 		goto retry;
 	}
 	if (unlikely(required)) {
+		nilfs_segctor_zeropad_segsum(sci);
 		err = nilfs_segbuf_extend_segsum(segbuf);
 		if (unlikely(err))
 			goto failed;
@@ -1544,6 +1563,7 @@ static int nilfs_segctor_collect(struct
 		nadd = min_t(int, nadd << 1, SC_MAX_SEGDELTA);
 		sci->sc_stage = prev_stage;
 	}
+	nilfs_segctor_zeropad_segsum(sci);
 	nilfs_segctor_truncate_segments(sci, sci->sc_curseg, nilfs->ns_sufile);
 	return 0;