On 2011-10-08, at 12:54 AM, Darrick J. Wong wrote: > 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. > > +static __u32 ext4_inode_csum(struct inode *inode, struct ext4_inode *raw, > + struct ext4_inode_info *ei) > +{ > + struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb); > + __u16 crc_lo; > + __u16 crc_hi = 0; > + __u32 crc; > + > + crc_lo = raw->i_checksum_lo; > + raw->i_checksum_lo = 0; > + if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE && > + EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi)) { > + crc_hi = raw->i_checksum_hi; > + raw->i_checksum_hi = 0; > + } > + > + crc = ext4_chksum(sbi, ei->i_uuid_inum_crc, (__u8 *)raw, > + EXT4_INODE_SIZE(inode->i_sb)); > + > + raw->i_checksum_lo = crc_lo; > + if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE && > + EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi)) > + raw->i_checksum_hi = crc_hi; > + > + return crc; > +} This computes both the _lo and _hi parts of the checksum and overwrites what is in the inode... > +static int ext4_inode_csum_verify(struct inode *inode, struct ext4_inode *raw, > + struct ext4_inode_info *ei) > +{ > + __u32 provided, calculated; > + > + if (EXT4_SB(inode->i_sb)->s_es->s_creator_os != > + cpu_to_le32(EXT4_OS_LINUX) || > + !EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb, > + EXT4_FEATURE_RO_COMPAT_METADATA_CSUM)) > + return 1; > + > + provided = le16_to_cpu(raw->i_checksum_lo); > + calculated = ext4_inode_csum(inode, raw, ei); This only saves the _lo part of the checksum before computing the new checksum (which overwrites both _lo and _hi fields), so the _hi part of the checksum is never properly validated below. > + if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE && > + EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi)) > + provided |= ((__u32)le16_to_cpu(raw->i_checksum_hi)) << 16; This should be moved up to save _hi before calling ext4_inode_csum(). > + else > + calculated &= 0xFFFF; > + > + return provided == calculated; > +} > +static void ext4_inode_csum_set(struct inode *inode, struct ext4_inode *raw, > + struct ext4_inode_info *ei) > +{ > + __u32 crc; > + > + if (EXT4_SB(inode->i_sb)->s_es->s_creator_os != > + cpu_to_le32(EXT4_OS_LINUX) || > + !EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb, > + EXT4_FEATURE_RO_COMPAT_METADATA_CSUM)) > + return; > + > + crc = ext4_inode_csum(inode, raw, ei); > + raw->i_checksum_lo = cpu_to_le16(crc & 0xFFFF); > + if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE && > + EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi)) > + raw->i_checksum_hi = cpu_to_le16(crc >> 16); What is the point of storing the returned crc into raw->i_checksum_lo and raw->i_checksum_hi, if this is done internal to ext4_inode_csum() already? Also, would it be better to call the temporary variable "csum" instead of "crc", since we may use something other than crc32c as the hash function in the future. Cheers, Andreas -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html