Re: [PATCH 15/16] ext4: Calculate and verify superblock checksum

From: Darrick J. Wong
Date: Fri Sep 02 2011 - 14:40:39 EST

On Thu, Sep 01, 2011 at 01:52:43AM -0600, Andreas Dilger wrote:
> On 2011-08-31, at 6:32 PM, Darrick J. Wong wrote:
> > Calculate and verify the superblock checksum. Since the UUID and block group
> > number are embedded in each copy of the superblock, we need only checksum the
> > entire block. Refactor some of the code to eliminate open-coding of the
> > checksum update call.
> >
> > Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
> > ---
> > fs/ext4/ext4.h | 8 +++++++-
> > fs/ext4/ext4_jbd2.c | 9 ++++++++-
> > fs/ext4/ext4_jbd2.h | 7 +++++--
> > fs/ext4/inode.c | 3 +--
> > fs/ext4/namei.c | 4 ++--
> > fs/ext4/resize.c | 6 +++++-
> > fs/ext4/super.c | 43 +++++++++++++++++++++++++++++++++++++++++++
> > 7 files changed, 71 insertions(+), 9 deletions(-)
> >
> >
> > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> > index b7aa5b5..1e93410 100644
> > --- a/fs/ext4/ext4.h
> > +++ b/fs/ext4/ext4.h
> > @@ -1067,7 +1067,9 @@ struct ext4_super_block {
> > __u8 s_last_error_func[32]; /* function where the error happened */
> > #define EXT4_S_ERR_END offsetof(struct ext4_super_block, s_mount_opts)
> > __u8 s_mount_opts[64];
> > - __le32 s_reserved[112]; /* Padding to the end of the block */
> > + __u32 s_reserved1[3]; /* Padding */
>
> Rather than mark these as reserved, it would be better to fill in the
> intended field names so that there is no confusion later on. I believe
> that there is s_usr_quota_inum and s_grp_quota_inum immediately following
> s_mount_opts, but I'm not sure what the 3rd reserved field is for.

"s_overhead_blocks", which I think is somehow related to bigalloc. They
haven't appeared in the kernel yet, which made me wary of adding fields that
aren't used by this patchset.

> > + __u32 s_checksum; /* crc32c(superblock) */
> > + __le32 s_reserved2[108]; /* Padding to the end of the block */
> > };
> >
> > #define EXT4_S_ERR_LEN (EXT4_S_ERR_END - EXT4_S_ERR_START)
> > @@ -1901,6 +1903,10 @@ extern int ext4_group_extend(struct super_block *sb,
> > ext4_fsblk_t n_blocks_count);
> >
> > /* super.c */
> > +extern int ext4_superblock_csum_verify(struct super_block *sb,
> > + struct ext4_super_block *es);
> > +extern void ext4_superblock_csum_set(struct super_block *sb,
> > + struct ext4_super_block *es);
> > extern void *ext4_kvmalloc(size_t size, gfp_t flags);
> > extern void *ext4_kvzalloc(size_t size, gfp_t flags);
> > extern void ext4_kvfree(void *ptr);
> > diff --git a/fs/ext4/ext4_jbd2.c b/fs/ext4/ext4_jbd2.c
> > index f5240aa..04ddc97 100644
> > --- a/fs/ext4/ext4_jbd2.c
> > +++ b/fs/ext4/ext4_jbd2.c
> > @@ -136,16 +136,23 @@ int __ext4_handle_dirty_metadata(const char *where, unsigned int line,
> > }
> >
> > int __ext4_handle_dirty_super(const char *where, unsigned int line,
> > - handle_t *handle, struct super_block *sb)
> > + handle_t *handle, struct super_block *sb,
> > + int now)
> > {
> > struct buffer_head *bh = EXT4_SB(sb)->s_sbh;
> > int err = 0;
> >
> > if (ext4_handle_valid(handle)) {
> > + ext4_superblock_csum_set(sb,
> > + (struct ext4_super_block *)bh->b_data);
> > err = jbd2_journal_dirty_metadata(handle, bh);
> > if (err)
> > ext4_journal_abort_handle(where, line, __func__,
> > bh, handle, err);
> > + } else if (now) {
> > + ext4_superblock_csum_set(sb,
> > + (struct ext4_super_block *)bh->b_data);
> > + mark_buffer_dirty(bh);
> > } else
> > sb->s_dirt = 1;
> > return err;
> > diff --git a/fs/ext4/ext4_jbd2.h b/fs/ext4/ext4_jbd2.h
> > index 5802fa1..ed9b78d 100644
> > --- a/fs/ext4/ext4_jbd2.h
> > +++ b/fs/ext4/ext4_jbd2.h
> > @@ -141,7 +141,8 @@ int __ext4_handle_dirty_metadata(const char *where, unsigned int line,
> > struct buffer_head *bh);
> >
> > int __ext4_handle_dirty_super(const char *where, unsigned int line,
> > - handle_t *handle, struct super_block *sb);
> > + handle_t *handle, struct super_block *sb,
> > + int now);
> >
> > #define ext4_journal_get_write_access(handle, bh) \
> > __ext4_journal_get_write_access(__func__, __LINE__, (handle), (bh))
> > @@ -153,8 +154,10 @@ int __ext4_handle_dirty_super(const char *where, unsigned int line,
> > #define ext4_handle_dirty_metadata(handle, inode, bh) \
> > __ext4_handle_dirty_metadata(__func__, __LINE__, (handle), (inode), \
> > (bh))
> > +#define ext4_handle_dirty_super_now(handle, sb) \
> > + __ext4_handle_dirty_super(__func__, __LINE__, (handle), (sb), 1)
> > #define ext4_handle_dirty_super(handle, sb) \
> > - __ext4_handle_dirty_super(__func__, __LINE__, (handle), (sb))
> > + __ext4_handle_dirty_super(__func__, __LINE__, (handle), (sb), 0)
> >
> > handle_t *ext4_journal_start_sb(struct super_block *sb, int nblocks);
> > int __ext4_journal_stop(const char *where, unsigned int line, handle_t *handle);
> > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > index e24ba98..52e9b67 100644
> > --- a/fs/ext4/inode.c
> > +++ b/fs/ext4/inode.c
> > @@ -3761,8 +3761,7 @@ static int ext4_do_update_inode(handle_t *handle,
> > EXT4_FEATURE_RO_COMPAT_LARGE_FILE);
> > sb->s_dirt = 1;
> > ext4_handle_sync(handle);
> > - err = ext4_handle_dirty_metadata(handle, NULL,
> > - EXT4_SB(sb)->s_sbh);
> > + err = ext4_handle_dirty_super_now(handle, sb);
> > }
> > }
> > raw_inode->i_generation = cpu_to_le32(inode->i_generation);
> > diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> > index 2d0fdb9..5ebf281 100644
> > --- a/fs/ext4/namei.c
> > +++ b/fs/ext4/namei.c
> > @@ -2407,7 +2407,7 @@ int ext4_orphan_add(handle_t *handle, struct inode *inode)
> > /* Insert this inode at the head of the on-disk orphan list... */
> > NEXT_ORPHAN(inode) = le32_to_cpu(EXT4_SB(sb)->s_es->s_last_orphan);
> > EXT4_SB(sb)->s_es->s_last_orphan = cpu_to_le32(inode->i_ino);
> > - err = ext4_handle_dirty_metadata(handle, NULL, EXT4_SB(sb)->s_sbh);
> > + err = ext4_handle_dirty_super_now(handle, sb);
> > rc = ext4_mark_iloc_dirty(handle, inode, &iloc);
> > if (!err)
> > err = rc;
> > @@ -2480,7 +2480,7 @@ int ext4_orphan_del(handle_t *handle, struct inode *inode)
> > if (err)
> > goto out_brelse;
> > sbi->s_es->s_last_orphan = cpu_to_le32(ino_next);
> > - err = ext4_handle_dirty_metadata(handle, NULL, sbi->s_sbh);
> > + err = ext4_handle_dirty_super_now(handle, inode->i_sb);
> > } else {
> > struct ext4_iloc iloc2;
> > struct inode *i_prev =
> > diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
> > index 707d3f1..2ad7008 100644
> > --- a/fs/ext4/resize.c
> > +++ b/fs/ext4/resize.c
> > @@ -511,7 +511,7 @@ static int add_new_gdb(handle_t *handle, struct inode *inode,
> > ext4_kvfree(o_group_desc);
> >
> > le16_add_cpu(&es->s_reserved_gdt_blocks, -1);
> > - err = ext4_handle_dirty_metadata(handle, NULL, EXT4_SB(sb)->s_sbh);
> > + err = ext4_handle_dirty_super_now(handle, sb);
> > if (err)
> > ext4_std_error(sb, err);
> >
> > @@ -682,6 +682,8 @@ static void update_backups(struct super_block *sb,
> > goto exit_err;
> > }
> >
> > + ext4_superblock_csum_set(sb, (struct ext4_super_block *)data);
> > +
> > while ((group = ext4_list_backups(sb, &three, &five, &seven)) < last) {
> > struct buffer_head *bh;
> >
> > @@ -925,6 +927,8 @@ int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input)
> > /* Update the global fs size fields */
> > sbi->s_groups_count++;
> >
> > + ext4_superblock_csum_set(sb,
> > + (struct ext4_super_block *)primary->b_data);
> > err = ext4_handle_dirty_metadata(handle, NULL, primary);
> > if (unlikely(err)) {
> > ext4_std_error(sb, err);
> > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> > index 44d0c8d..b254274 100644
> > --- a/fs/ext4/super.c
> > +++ b/fs/ext4/super.c
> > @@ -38,6 +38,7 @@
> > #include <linux/ctype.h>
> > #include <linux/log2.h>
> > #include <linux/crc16.h>
> > +#include <linux/crc32c.h>
> > #include <linux/cleancache.h>
> > #include <asm/uaccess.h>
> >
> > @@ -110,6 +111,41 @@ static struct file_system_type ext3_fs_type = {
> > #define IS_EXT3_SB(sb) (0)
> > #endif
> >
> > +static __le32 ext4_superblock_csum(struct super_block *sb,
> > + struct ext4_super_block *es)
> > +{
> > + int offset = offsetof(struct ext4_super_block, s_checksum);
> > + __u32 crc = 0;
> > +
> > + if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
> > + EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
> > + return 0;
> > +
> > + crc = crc32c_le(~0, (char *)es, offset);
>
> For consistency, shouldn't this also checksum the fields _after_ offset?
> Otherwise, if new fields are used after s_checksum the update to this
> function may easily be missed, and those new fields would not be covered
> by the checksum. It also means the superblock checksum would be different
> based on which kernel is being used (based on which fields it knows about.

Actually, I had pondered putting the checksum at the very end of the 1k
superblock, which makes the checksum cover the padding too. On the other hand,
I thought I might save us ~400b of crc32c computation time. I don't have a big
objection to crc'ing all the padding.

--D
>
> > +
> > + return cpu_to_le32(crc);
> > +}
> > +
> > +int ext4_superblock_csum_verify(struct super_block *sb,
> > + struct ext4_super_block *es)
> > +{
> > + if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
> > + EXT4_FEATURE_RO_COMPAT_METADATA_CSUM) &&
> > + (es->s_checksum != ext4_superblock_csum(sb, es)))
> > + return 0;
> > + return 1;
> > +}
> > +
> > +void ext4_superblock_csum_set(struct super_block *sb,
> > + struct ext4_super_block *es)
> > +{
> > + if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
> > + EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
> > + return;
> > +
> > + es->s_checksum = ext4_superblock_csum(sb, es);
> > +}
> > +
> > void *ext4_kvmalloc(size_t size, gfp_t flags)
> > {
> > void *ret;
> > @@ -3151,6 +3187,12 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> > sb->s_magic = le16_to_cpu(es->s_magic);
> > if (sb->s_magic != EXT4_SUPER_MAGIC)
> > goto cantfind_ext4;
> > + if (!ext4_superblock_csum_verify(sb, es)) {
> > + ext4_msg(sb, KERN_ERR, "VFS: Found ext4 filesystem with "
> > + "invalid superblock checksum. Run e2fsck?");
> > + silent = 1;
> > + goto cantfind_ext4;
> > + }
> > sbi->s_kbytes_written = le64_to_cpu(es->s_kbytes_written);
> >
> > /* Set defaults before we parse the mount options */
> > @@ -4107,6 +4149,7 @@ static int ext4_commit_super(struct super_block *sb, int sync)
> > &EXT4_SB(sb)->s_freeinodes_counter));
> > sb->s_dirt = 0;
> > BUFFER_TRACE(sbh, "marking dirty");
> > + ext4_superblock_csum_set(sb, es);
> > mark_buffer_dirty(sbh);
> > if (sync) {
> > error = sync_dirty_buffer(sbh);
> >
>
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