Eric Biggers <ebigg...@kernel.org> writes:
> From: Eric Biggers <ebigg...@google.com>
>
> It is invalid for the casefold inode flag to be set without the casefold
> superblock feature flag also being set. e2fsck already considers this
> case to be invalid and handles it by offering to clear the casefold flag
> on the inode. __ext4_iget() also already considered this to be invalid,
> sort of, but it only got so far as logging an error message; it didn't
> actually reject the inode. Make it reject the inode so that other code
> doesn't have to handle this case. This matches what f2fs does.
>
> Note: we could check 's_encoding != NULL' instead of
> ext4_has_feature_casefold(). This would make the check robust against
> the casefold feature being enabled by userspace writing to the page
> cache of the mounted block device. However, it's unsolvable in general
> for filesystems to be robust against concurrent writes to the page cache
> of the mounted block device. Though this very particular scenario
> involving the casefold feature is solvable, we should not pretend that
> we can support this model, so let's just check the casefold feature.
> tune2fs already forbids enabling casefold on a mounted filesystem.
just because we can't fix the general issue for the entire filesystem
doesn't mean this case *must not* ever be addressed. What is the
advantage of making the code less robust against the syzbot code? Just
check sb->s_encoding and be safe later knowing the unicode map is
available.
>
> Signed-off-by: Eric Biggers <ebigg...@google.com>
> ---
> fs/ext4/inode.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 43775a6ca505..390dedbb7e8a 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4940,9 +4940,12 @@ struct inode *__ext4_iget(struct super_block *sb,
> unsigned long ino,
> "iget: bogus i_mode (%o)", inode->i_mode);
> goto bad_inode;
> }
> - if (IS_CASEFOLDED(inode) && !ext4_has_feature_casefold(inode->i_sb))
> + if (IS_CASEFOLDED(inode) && !ext4_has_feature_casefold(inode->i_sb)) {
> ext4_error_inode(inode, function, line, 0,
> "casefold flag without casefold feature");
> + ret = -EFSCORRUPTED;
> + goto bad_inode;
> + }
> if ((err_str = check_igot_inode(inode, flags)) != NULL) {
> ext4_error_inode(inode, function, line, 0, err_str);
> ret = -EFSCORRUPTED;
--
Gabriel Krisman Bertazi
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