Re: [PATCH v3 3/4] ext4: add EXT4_IGET_BAD flag to prevent unexpected bad inode

Jan Kara
2022-10-26T09:41:52Z

On Wed 26-10-22 12:23:09, Baokun Li wrote:
> There are many places that will get unhappy (and crash) when ext4_iget()
> returns a bad inode. However, if iget the boot loader inode, allows a bad
> inode to be returned, because the inode may not be initialized. This
> mechanism can be used to bypass some checks and cause panic. To solve this
> problem, we add a special iget flag EXT4_IGET_BAD. Only with this flag
> we'd be returning bad inode from ext4_iget(), otherwise we always return
> the error code if the inode is bad inode.(suggested by Jan Kara)
>
> Signed-off-by: Baokun Li <libaokun1@huawei.com>

Looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> ---
> fs/ext4/ext4.h | 3 ++-
> fs/ext4/inode.c | 8 +++++++-
> fs/ext4/ioctl.c | 3 ++-
> 3 files changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 8d5453852f98..2b574b143bde 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -2964,7 +2964,8 @@ int do_journal_get_write_access(handle_t *handle, struct inode *inode,
> typedef enum {
> EXT4_IGET_NORMAL = 0,
> EXT4_IGET_SPECIAL = 0x0001, /* OK to iget a system inode */
> - EXT4_IGET_HANDLE = 0x0002 /* Inode # is from a handle */
> + EXT4_IGET_HANDLE = 0x0002, /* Inode # is from a handle */
> + EXT4_IGET_BAD = 0x0004 /* Allow to iget a bad inode */
> } ext4_iget_flags;
>
> extern struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index ae3a836dd9d7..f767340229fd 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -5043,8 +5043,14 @@ struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
> if (IS_CASEFOLDED(inode) && !ext4_has_feature_casefold(inode->i_sb))
> ext4_error_inode(inode, function, line, 0,
> "casefold flag without casefold feature");
> - brelse(iloc.bh);
> + if (is_bad_inode(inode) && !(flags & EXT4_IGET_BAD)) {
> + ext4_error_inode(inode, function, line, 0,
> + "bad inode without EXT4_IGET_BAD flag");
> + ret = -EUCLEAN;
> + goto bad_inode;
> + }
>
> + brelse(iloc.bh);
> unlock_new_inode(inode);
> return inode;
>
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index ded535535b27..e0be8026c996 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -375,7 +375,8 @@ static long swap_inode_boot_loader(struct super_block *sb,
> blkcnt_t blocks;
> unsigned short bytes;
>
> - inode_bl = ext4_iget(sb, EXT4_BOOT_LOADER_INO, EXT4_IGET_SPECIAL);
> + inode_bl = ext4_iget(sb, EXT4_BOOT_LOADER_INO,
> + EXT4_IGET_SPECIAL | EXT4_IGET_BAD);
> if (IS_ERR(inode_bl))
> return PTR_ERR(inode_bl);
> ei_bl = EXT4_I(inode_bl);
> --
> 2.31.1
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR