f2fs: cover large section in sanity check of super

This patch fixes the bug which does not cover a large section case when checking
the sanity of superblock.
If f2fs detects misalignment, it will fix the superblock during the mount time,
so it doesn't need to trigger fsck.f2fs further.
Reported-by: Matthias Prager <linux@matthiasprager.de>
Reported-by: David Gnedt <david.gnedt@davizone.at>
Cc: stable 4.5+ <stable@vger.kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -984,9 +984,25 @@ static loff_t max_file_blocks(void)
 	return result;
 }
 
+static int __f2fs_commit_super(struct buffer_head *bh,
+			struct f2fs_super_block *super)
+{
+	lock_buffer(bh);
+	if (super)
+		memcpy(bh->b_data + F2FS_SUPER_OFFSET, super, sizeof(*super));
+	set_buffer_uptodate(bh);
+	set_buffer_dirty(bh);
+	unlock_buffer(bh);
+
+	/* it's rare case, we can do fua all the time */
+	return __sync_dirty_buffer(bh, WRITE_FLUSH_FUA);
+}
+
 static inline bool sanity_check_area_boundary(struct super_block *sb,
-					struct f2fs_super_block *raw_super)
+					struct buffer_head *bh)
 {
+	struct f2fs_super_block *raw_super = (struct f2fs_super_block *)
+					(bh->b_data + F2FS_SUPER_OFFSET);
 	u32 segment0_blkaddr = le32_to_cpu(raw_super->segment0_blkaddr);
 	u32 cp_blkaddr = le32_to_cpu(raw_super->cp_blkaddr);
 	u32 sit_blkaddr = le32_to_cpu(raw_super->sit_blkaddr);
@@ -1000,6 +1016,10 @@ static inline bool sanity_check_area_boundary(struct super_block *sb,
 	u32 segment_count_main = le32_to_cpu(raw_super->segment_count_main);
 	u32 segment_count = le32_to_cpu(raw_super->segment_count);
 	u32 log_blocks_per_seg = le32_to_cpu(raw_super->log_blocks_per_seg);
+	u64 main_end_blkaddr = main_blkaddr +
+				(segment_count_main << log_blocks_per_seg);
+	u64 seg_end_blkaddr = segment0_blkaddr +
+				(segment_count << log_blocks_per_seg);
 
 	if (segment0_blkaddr != cp_blkaddr) {
 		f2fs_msg(sb, KERN_INFO,
@@ -1044,22 +1064,45 @@ static inline bool sanity_check_area_boundary(struct super_block *sb,
 		return true;
 	}
 
-	if (main_blkaddr + (segment_count_main << log_blocks_per_seg) !=
-		segment0_blkaddr + (segment_count << log_blocks_per_seg)) {
+	if (main_end_blkaddr > seg_end_blkaddr) {
 		f2fs_msg(sb, KERN_INFO,
-			"Wrong MAIN_AREA boundary, start(%u) end(%u) blocks(%u)",
+			"Wrong MAIN_AREA boundary, start(%u) end(%u) block(%u)",
 			main_blkaddr,
-			segment0_blkaddr + (segment_count << log_blocks_per_seg),
+			segment0_blkaddr +
+				(segment_count << log_blocks_per_seg),
 			segment_count_main << log_blocks_per_seg);
 		return true;
+	} else if (main_end_blkaddr < seg_end_blkaddr) {
+		int err = 0;
+		char *res;
+
+		/* fix in-memory information all the time */
+		raw_super->segment_count = cpu_to_le32((main_end_blkaddr -
+				segment0_blkaddr) >> log_blocks_per_seg);
+
+		if (f2fs_readonly(sb) || bdev_read_only(sb->s_bdev)) {
+			res = "internally";
+		} else {
+			err = __f2fs_commit_super(bh, NULL);
+			res = err ? "failed" : "done";
+		}
+		f2fs_msg(sb, KERN_INFO,
+			"Fix alignment : %s, start(%u) end(%u) block(%u)",
+			res, main_blkaddr,
+			segment0_blkaddr +
+				(segment_count << log_blocks_per_seg),
+			segment_count_main << log_blocks_per_seg);
+		if (err)
+			return true;
 	}
-
 	return false;
 }
 
 static int sanity_check_raw_super(struct super_block *sb,
-			struct f2fs_super_block *raw_super)
+				struct buffer_head *bh)
 {
+	struct f2fs_super_block *raw_super = (struct f2fs_super_block *)
+					(bh->b_data + F2FS_SUPER_OFFSET);
 	unsigned int blocksize;
 
 	if (F2FS_SUPER_MAGIC != le32_to_cpu(raw_super->magic)) {
@@ -1126,7 +1169,7 @@ static int sanity_check_raw_super(struct super_block *sb,
 	}
 
 	/* check CP/SIT/NAT/SSA/MAIN_AREA area boundary */
-	if (sanity_check_area_boundary(sb, raw_super))
+	if (sanity_check_area_boundary(sb, bh))
 		return 1;
 
 	return 0;
@@ -1202,7 +1245,7 @@ static int read_raw_super_block(struct super_block *sb,
 {
 	int block;
 	struct buffer_head *bh;
-	struct f2fs_super_block *super, *buf;
+	struct f2fs_super_block *super;
 	int err = 0;
 
 	super = kzalloc(sizeof(struct f2fs_super_block), GFP_KERNEL);
@@ -1218,11 +1261,8 @@ static int read_raw_super_block(struct super_block *sb,
 			continue;
 		}
 
-		buf = (struct f2fs_super_block *)
-				(bh->b_data + F2FS_SUPER_OFFSET);
-
 		/* sanity checking of raw super */
-		if (sanity_check_raw_super(sb, buf)) {
+		if (sanity_check_raw_super(sb, bh)) {
 			f2fs_msg(sb, KERN_ERR,
 				"Can't find valid F2FS filesystem in %dth superblock",
 				block + 1);
@@ -1232,7 +1272,8 @@ static int read_raw_super_block(struct super_block *sb,
 		}
 
 		if (!*raw_super) {
-			memcpy(super, buf, sizeof(*super));
+			memcpy(super, bh->b_data + F2FS_SUPER_OFFSET,
+							sizeof(*super));
 			*valid_super_block = block;
 			*raw_super = super;
 		}
@@ -1252,42 +1293,29 @@ static int read_raw_super_block(struct super_block *sb,
 	return err;
 }
 
-static int __f2fs_commit_super(struct f2fs_sb_info *sbi, int block)
+int f2fs_commit_super(struct f2fs_sb_info *sbi, bool recover)
 {
-	struct f2fs_super_block *super = F2FS_RAW_SUPER(sbi);
 	struct buffer_head *bh;
 	int err;
 
-	bh = sb_getblk(sbi->sb, block);
+	/* write back-up superblock first */
+	bh = sb_getblk(sbi->sb, sbi->valid_super_block ? 0: 1);
 	if (!bh)
 		return -EIO;
-
-	lock_buffer(bh);
-	memcpy(bh->b_data + F2FS_SUPER_OFFSET, super, sizeof(*super));
-	set_buffer_uptodate(bh);
-	set_buffer_dirty(bh);
-	unlock_buffer(bh);
-
-	/* it's rare case, we can do fua all the time */
-	err = __sync_dirty_buffer(bh, WRITE_FLUSH_FUA);
+	err = __f2fs_commit_super(bh, F2FS_RAW_SUPER(sbi));
 	brelse(bh);
 
-	return err;
-}
-
-int f2fs_commit_super(struct f2fs_sb_info *sbi, bool recover)
-{
-	int err;
-
-	/* write back-up superblock first */
-	err = __f2fs_commit_super(sbi, sbi->valid_super_block ? 0 : 1);
-
 	/* if we are in recovery path, skip writing valid superblock */
 	if (recover || err)
 		return err;
 
 	/* write current valid superblock */
-	return __f2fs_commit_super(sbi, sbi->valid_super_block);
+	bh = sb_getblk(sbi->sb, sbi->valid_super_block);
+	if (!bh)
+		return -EIO;
+	err = __f2fs_commit_super(bh, F2FS_RAW_SUPER(sbi));
+	brelse(bh);
+	return err;
 }
 
 static int f2fs_fill_super(struct super_block *sb, void *data, int silent)