[LogFS] Plug 8 byte information leak

Within each journal segment, 8 bytes at offset 24 would remain
uninitialized.
Signed-off-by: Joern Engel <joern@logfs.org>

fs/logfs/journal.c

@@ -388,7 +388,10 @@ static void journal_get_erase_count(struct logfs_area *area)
 static int journal_erase_segment(struct logfs_area *area)
 {
 	struct super_block *sb = area->a_sb;
-	struct logfs_segment_header sh;
+	union {
+		struct logfs_segment_header sh;
+		unsigned char c[ALIGN(sizeof(struct logfs_segment_header), 16)];
+	} u;
 	u64 ofs;
 	int err;
 
@@ -396,20 +399,21 @@ static int journal_erase_segment(struct logfs_area *area)
 	if (err)
 		return err;
 
-	sh.pad = 0;
-	sh.type = SEG_JOURNAL;
-	sh.level = 0;
-	sh.segno = cpu_to_be32(area->a_segno);
-	sh.ec = cpu_to_be32(area->a_erase_count);
-	sh.gec = cpu_to_be64(logfs_super(sb)->s_gec);
-	sh.crc = logfs_crc32(&sh, sizeof(sh), 4);
+	memset(&u, 0, sizeof(u));
+	u.sh.pad = 0;
+	u.sh.type = SEG_JOURNAL;
+	u.sh.level = 0;
+	u.sh.segno = cpu_to_be32(area->a_segno);
+	u.sh.ec = cpu_to_be32(area->a_erase_count);
+	u.sh.gec = cpu_to_be64(logfs_super(sb)->s_gec);
+	u.sh.crc = logfs_crc32(&u.sh, sizeof(u.sh), 4);
 
 	/* This causes a bug in segment.c.  Not yet. */
 	//logfs_set_segment_erased(sb, area->a_segno, area->a_erase_count, 0);
 
 	ofs = dev_ofs(sb, area->a_segno, 0);
-	area->a_used_bytes = ALIGN(sizeof(sh), 16);
-	logfs_buf_write(area, ofs, &sh, sizeof(sh));
+	area->a_used_bytes = sizeof(u);
+	logfs_buf_write(area, ofs, &u, sizeof(u));
 	return 0;
 }