[PATCH v2 2/2] f2fs: relocate chksum_offset for large_nat_bitmap feature

From: Chao Yu <yuchao0@huawei.com>
To: <jaegeuk@kernel.org>
Cc: <linux-f2fs-devel@lists.sourceforge.net>,
	<linux-kernel@vger.kernel.org>, <chao@kernel.org>,
	Chao Yu <yuchao0@huawei.com>
Subject: [PATCH v2 2/2] f2fs: relocate chksum_offset for large_nat_bitmap feature
Date: Fri, 26 Apr 2019 10:25:54 +0800	[thread overview]
Message-ID: <20190426022554.56393-1-yuchao0@huawei.com> (raw)

For large_nat_bitmap feature, there is a design flaw:

Previous:

struct f2fs_checkpoint layout:
+--------------------------+  0x0000
| checkpoint_ver           |
| ......                   |
| checksum_offset          |------+
| ......                   |      |
| sit_nat_version_bitmap[] |<-----|-------+
| ......                   |      |       |
| checksum_value           |<-----+       |
+--------------------------+  0x1000      |
|                          |      nat_bitmap + sit_bitmap
| payload blocks           |              |
|                          |              |
+--------------------------|<-------------+

Obviously, if nat_bitmap size + sit_bitmap size is larger than
MAX_BITMAP_SIZE_IN_CKPT, nat_bitmap or sit_bitmap may overlap
checkpoint checksum's position, once checkpoint() is triggered
from kernel, nat or sit bitmap will be damaged by checksum field.

In order to fix this, let's relocate checksum_value's position
to the head of sit_nat_version_bitmap as below, then nat/sit
bitmap and chksum value update will become safe.

After:

struct f2fs_checkpoint layout:
+--------------------------+  0x0000
| checkpoint_ver           |
| ......                   |
| checksum_offset          |------+
| ......                   |      |
| sit_nat_version_bitmap[] |<-----+
| ......                   |<-------------+
|                          |              |
+--------------------------+  0x1000      |
|                          |      nat_bitmap + sit_bitmap
| payload blocks           |              |
|                          |              |
+--------------------------|<-------------+

Related report and discussion:

https://sourceforge.net/p/linux-f2fs/mailman/message/36642346/

Reported-by: Park Ju Hyung <qkrwngud825@gmail.com>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
---
v2:
- improve hint message suggested by Ju Hyung.
- move verification to f2fs_sanity_check_ckpt().
 fs/f2fs/f2fs.h  |  4 +++-
 fs/f2fs/super.c | 13 +++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 119bc5a9783e..aa71c1aa9eaa 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1909,9 +1909,11 @@ static inline void *__bitmap_ptr(struct f2fs_sb_info *sbi, int flag)
 	int offset;
 
 	if (is_set_ckpt_flags(sbi, CP_LARGE_NAT_BITMAP_FLAG)) {
+		unsigned int chksum_size = sizeof(__le32);
+
 		offset = (flag == SIT_BITMAP) ?
 			le32_to_cpu(ckpt->nat_ver_bitmap_bytesize) : 0;
-		return &ckpt->sit_nat_version_bitmap + offset;
+		return &ckpt->sit_nat_version_bitmap + offset + chksum_size;
 	}
 
 	if (__cp_payload(sbi) > 0) {
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index fefc8cc6e756..22241bb866df 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -2714,6 +2714,19 @@ int f2fs_sanity_check_ckpt(struct f2fs_sb_info *sbi)
 		return 1;
 	}
 
+	if (__is_set_ckpt_flags(ckpt, CP_LARGE_NAT_BITMAP_FLAG)) {
+		unsigned int chksum_offset;
+
+		chksum_offset = le32_to_cpu(ckpt->checksum_offset);
+		if (chksum_offset != CP_MIN_CHKSUM_OFFSET) {
+			f2fs_msg(sbi->sb, KERN_WARNING,
+				"using deprecated layout of large_nat_bitmap, "
+				"please run fsck v1.13.0 or higher to repair, "
+				"chksum_offset: %u", chksum_offset);
+			return 1;
+		}
+	}
+
 	if (unlikely(f2fs_cp_error(sbi))) {
 		f2fs_msg(sbi->sb, KERN_ERR, "A bug case: need to run fsck");
 		return 1;
-- 
2.18.0.rc1

