[PATCH 1/2] ext4: Calculate and verify inode checksums

["Darrick J. Wong" <djwong@us.ibm.com>]

This patch introduces to ext4 the ability to calculate and verify inode
checksums.  This requires the use of a new ro compatibility flag and some
accompanying e2fsprogs patches to provide the relevant features in tune2fs and
e2fsck.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
---

 fs/ext4/ext4.h  |    6 ++++--
 fs/ext4/inode.c |   52 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 55 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 4daaf2b..8815928 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -617,7 +617,7 @@ struct ext4_inode {
 		} masix2;
 	} osd2;				/* OS dependent 2 */
 	__le16	i_extra_isize;
-	__le16	i_pad1;
+	__le16  i_checksum;		/* crc16(sb_uuid+inodenum+inode) */
 	__le32  i_ctime_extra;  /* extra Change time      (nsec << 2 | epoch) */
 	__le32  i_mtime_extra;  /* extra Modification time(nsec << 2 | epoch) */
 	__le32  i_atime_extra;  /* extra Access time      (nsec << 2 | epoch) */
@@ -1338,6 +1338,7 @@ static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
 #define EXT4_FEATURE_RO_COMPAT_GDT_CSUM		0x0010
 #define EXT4_FEATURE_RO_COMPAT_DIR_NLINK	0x0020
 #define EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE	0x0040
+#define EXT4_FEATURE_RO_COMPAT_INODE_CSUM	0x0400
 
 #define EXT4_FEATURE_INCOMPAT_COMPRESSION	0x0001
 #define EXT4_FEATURE_INCOMPAT_FILETYPE		0x0002
@@ -1364,7 +1365,8 @@ static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
 					 EXT4_FEATURE_RO_COMPAT_DIR_NLINK | \
 					 EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE | \
 					 EXT4_FEATURE_RO_COMPAT_BTREE_DIR |\
-					 EXT4_FEATURE_RO_COMPAT_HUGE_FILE)
+					 EXT4_FEATURE_RO_COMPAT_HUGE_FILE |\
+					 EXT4_FEATURE_RO_COMPAT_INODE_CSUM)
 
 /*
  * Default values for user and/or group using reserved blocks
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 1a86282..dc76f19 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -42,6 +42,7 @@
 #include <linux/printk.h>
 #include <linux/slab.h>
 #include <linux/ratelimit.h>
+#include <linux/crc16.h>
 
 #include "ext4_jbd2.h"
 #include "xattr.h"
@@ -52,6 +53,40 @@
 
 #define MPAGE_DA_EXTENT_TAIL 0x01
 
+static __le16 ext4_inode_csum(struct inode *inode, struct ext4_inode *raw)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
+	struct ext4_inode_info *ei = EXT4_I(inode);
+	int offset = offsetof(struct ext4_inode, i_checksum);
+	__le32 inum = cpu_to_le32(inode->i_ino);
+	__u16 crc = 0;
+
+	if (EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb,
+		EXT4_FEATURE_RO_COMPAT_INODE_CSUM) &&
+	    le16_to_cpu(raw->i_extra_isize) >= 4) {
+		crc = crc16(~0, sbi->s_es->s_uuid, sizeof(sbi->s_es->s_uuid));
+		crc = crc16(crc, (__u8 *)&inum, sizeof(inum));
+		crc = crc16(crc, (__u8 *)raw, offset);
+		offset += sizeof(raw->i_checksum); /* skip checksum */
+		/* for checksum of struct ext4_inode do the rest...*/
+		if (ei->i_extra_isize > 4)
+			crc = crc16(crc, (__u8 *)raw + offset,
+				    ei->i_extra_isize - 4);
+	}
+
+	return cpu_to_le16(crc);
+}
+
+static int ext4_inode_csum_verify(struct inode *inode, struct ext4_inode *raw)
+{
+	if (EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb,
+		EXT4_FEATURE_RO_COMPAT_INODE_CSUM) &&
+	    (raw->i_checksum != ext4_inode_csum(inode, raw)))
+		return 0;
+
+	return 1;
+}
+
 static inline int ext4_begin_ordered_truncate(struct inode *inode,
 					      loff_t new_size)
 {
@@ -4802,7 +4837,8 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
 	struct ext4_inode *raw_inode;
 	struct ext4_inode_info *ei;
 	struct inode *inode;
-	journal_t *journal = EXT4_SB(sb)->s_journal;
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	journal_t *journal = sbi->s_journal;
 	long ret;
 	int block;
 
@@ -4916,6 +4952,14 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
 	} else
 		ei->i_extra_isize = 0;
 
+	if (!ext4_inode_csum_verify(inode, raw_inode)) {
+		EXT4_ERROR_INODE(inode, "checksum invalid (%u != %u)",
+		       le16_to_cpu(ext4_inode_csum(inode, raw_inode)),
+		       le16_to_cpu(raw_inode->i_checksum));
+		ret = -EIO;
+		goto bad_inode;
+	}
+
 	EXT4_INODE_GET_XTIME(i_ctime, inode, raw_inode);
 	EXT4_INODE_GET_XTIME(i_mtime, inode, raw_inode);
 	EXT4_INODE_GET_XTIME(i_atime, inode, raw_inode);
@@ -5138,6 +5182,12 @@ static int ext4_do_update_inode(handle_t *handle,
 			raw_inode->i_version_hi =
 			cpu_to_le32(inode->i_version >> 32);
 		raw_inode->i_extra_isize = cpu_to_le16(ei->i_extra_isize);
+
+		if (EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb,
+			EXT4_FEATURE_RO_COMPAT_INODE_CSUM) &&
+		    EXT4_FITS_IN_INODE(raw_inode, ei, i_checksum))
+			raw_inode->i_checksum =
+				ext4_inode_csum(inode, raw_inode);
 	}
 
 	BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");