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    SubjectRe: [PATCH 1/2] ext4: Calculate and verify inode checksums
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    On 2011-04-06, at 4:45 PM, 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.
    >
    > 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) */

    In previous discussions, we thought about using part/all of the l_i_reserved2 field to store the inode checksum. The inode checksum is important enough to warrant a field in the core inode, so that it also works on upgraded filesystems.

    > +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) {

    If this field remains in the large part of the inode, then this check is incorrect. i_extra_isize is itself only valid if (s_inode_size is > EXT4_GOOD_OLD_INODE_SIZE), otherwise it points at the next inode's i_mode.

    Also, instead of hard-coding ">= 4" here, it would be better to use EXT4_FITS_IN_INODE(raw, EXT4_I(inode), i_checksum). Probably no reason to put "ei" on the stack at all.

    > + 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");


    Cheers, Andreas






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