Re: [PATCH 4/8] vfs: Fold casefolding into vfs

Gabriel Krisman Bertazi
2019-12-03T21:21:10Z

Eric Biggers <ebiggers@kernel.org> writes:

> On Tue, Dec 03, 2019 at 02:42:10PM -0500, Gabriel Krisman Bertazi wrote:
>> Gao Xiang <gaoxiang25@huawei.com> writes:

>> I think Daniel's approach of moving this into VFS is the simplest way to
>> actually solve the issue, instead of extending and duplicating a lot of
>> functionality into filesystem hooks to support the possible mixes of
>> case-insensitive, overlayfs and fscrypt.
>>
>
> I think we can actually get everything we want using dentry_operations only,
> since the filesystem can set ->d_op during ->lookup() (like what is done for
> encrypted filenames now) rather than at dentry allocation time. And fs/crypto/
> can export fscrypt_d_revalidate() rather than setting ->d_op itself.

Problem is, differently from fscrypt, case-insensitive uses the d_hash()
hook and for a lookup, we actually use
dentry->d_parent->d_ops->d_hash(). Which works well, until you are flipping the
casefold flag. Then the dentry already exists and you need to modify
the d_ops on the fly, which I couldn't find precedent anywhere. I tried
invalidating the dentry whenever we flip the flag, but then if it has
negative dentries as children,I wasn't able to reliably invalidate it,
and that's when I reached the limit of my knowledge in VFS. In
particular, in every attempt I made to implement it like this, I was
able to race and do a case-insensitive lookup on a directory that was
just made case sensitive.

I'm not saying there isn't a way. But it is a bit harder than this
proposal. I tried it already and still didn't manage to make it work.
Maybe someone who better understands vfs.

> It's definitely ugly to have to handle the 3 cases of encrypt, casefold, and
> encrypt+casefold separately -- and this will need to be duplicated for each
> filesystem. But we do have to weigh that against adding additional complexity
> and overhead to the VFS for everyone. If we do go with the VFS changes, please
> try to make them as simple and unobtrusive as possible.

Well, it is just not case-insensitive+fscrypt. Also overlayfs
there. Probably more. So we have much more cases. I understand the VFS
changes need to be very well thought, but when I worked on this it
started to look a more correct solution than using the hooks.

> diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c
> index 3719efa546c6..cfa44adff2b3 100644
> --- a/fs/crypto/crypto.c
> +++ b/fs/crypto/crypto.c
> @@ -290,7 +290,7 @@ EXPORT_SYMBOL(fscrypt_decrypt_block_inplace);
> * Validate dentries in encrypted directories to make sure we aren't potentially
> * caching stale dentries after a key has been added.
> */
> -static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
> +int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
> {
> struct dentry *dir;
> int err;
> @@ -329,10 +329,7 @@ static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
>
> return valid;
> }
> -
> -const struct dentry_operations fscrypt_d_ops = {
> - .d_revalidate = fscrypt_d_revalidate,
> -};
> +EXPORT_SYMBOL_GPL(fscrypt_d_revalidate);
>
> /**
> * fscrypt_initialize() - allocate major buffers for fs encryption.
> diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
> index 130b50e5a011..4420670ac40a 100644
> --- a/fs/crypto/fscrypt_private.h
> +++ b/fs/crypto/fscrypt_private.h
> @@ -233,7 +233,6 @@ extern int fscrypt_crypt_block(const struct inode *inode,
> unsigned int len, unsigned int offs,
> gfp_t gfp_flags);
> extern struct page *fscrypt_alloc_bounce_page(gfp_t gfp_flags);
> -extern const struct dentry_operations fscrypt_d_ops;
>
> extern void __printf(3, 4) __cold
> fscrypt_msg(const struct inode *inode, const char *level, const char *fmt, ...);
> diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
> index bb3b7fcfdd48..ec81b6a597aa 100644
> --- a/fs/crypto/hooks.c
> +++ b/fs/crypto/hooks.c
> @@ -116,7 +116,6 @@ int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
> spin_lock(&dentry->d_lock);
> dentry->d_flags |= DCACHE_ENCRYPTED_NAME;
> spin_unlock(&dentry->d_lock);
> - d_set_d_op(dentry, &fscrypt_d_ops);
> }
> return err;
> }
> diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
> index 9fdd2b269d61..bd3c14e6b24a 100644
> --- a/fs/ext4/dir.c
> +++ b/fs/ext4/dir.c
> @@ -704,9 +704,47 @@ static int ext4_d_hash(const struct dentry *dentry, struct qstr *str)
> kfree(norm);
> return ret;
> }
> +#endif /* !CONFIG_UNICODE */
>
> -const struct dentry_operations ext4_dentry_ops = {
> +#ifdef CONFIG_UNICODE
> +static const struct dentry_operations ext4_ci_dentry_ops = {
> + .d_hash = ext4_d_hash,
> + .d_compare = ext4_d_compare,
> +};
> +#endif
> +
> +#ifdef CONFIG_FS_ENCRYPTION
> +static const struct dentry_operations ext4_encrypted_dentry_ops = {
> + .d_revalidate = fscrypt_d_revalidate,
> +};
> +#endif
> +
> +#if IS_ENABLED(CONFIG_UNICODE) && IS_ENABLED(CONFIG_FS_ENCRYPTION)
> +static const struct dentry_operations ext4_encrypted_ci_dentry_ops = {
> .d_hash = ext4_d_hash,
> .d_compare = ext4_d_compare,
> + .d_revalidate = fscrypt_d_revalidate,
> };
> #endif
> +
> +void ext4_set_d_ops(struct inode *dir, struct dentry *dentry)
> +{
> +#ifdef CONFIG_FS_ENCRYPTION
> + if (dentry->d_flags & DCACHE_ENCRYPTED_NAME) {
> +#ifdef CONFIG_UNICODE
> + if (IS_CASEFOLDED(dir)) {
> + d_set_d_op(dentry, &ext4_encrypted_ci_dentry_ops);
> + return;
> + }
> +#endif
> + d_set_d_op(dentry, &ext4_encrypted_dentry_ops);
> + return;
> + }
> +#endif
> +#ifdef CONFIG_UNICODE
> + if (IS_CASEFOLDED(dir)) {
> + d_set_d_op(dentry, &ext4_ci_dentry_ops);
> + return;
> + }
> +#endif
> +}
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index f8578caba40d..00a10015a53c 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -2499,6 +2499,8 @@ static inline unsigned char get_dtype(struct super_block *sb, int filetype)
> extern int ext4_check_all_de(struct inode *dir, struct buffer_head *bh,
> void *buf, int buf_size);
>
> +void ext4_set_d_ops(struct inode *dir, struct dentry *dentry);
> +
> /* fsync.c */
> extern int ext4_sync_file(struct file *, loff_t, loff_t, int);
>
> @@ -3097,10 +3099,6 @@ static inline void ext4_unlock_group(struct super_block *sb,
> /* dir.c */
> extern const struct file_operations ext4_dir_operations;
>
> -#ifdef CONFIG_UNICODE
> -extern const struct dentry_operations ext4_dentry_ops;
> -#endif
> -
> /* file.c */
> extern const struct inode_operations ext4_file_inode_operations;
> extern const struct file_operations ext4_file_operations;
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index a856997d87b5..4df1d074b393 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -1608,6 +1608,7 @@ static struct buffer_head *ext4_lookup_entry(struct inode *dir,
> struct buffer_head *bh;
>
> err = ext4_fname_prepare_lookup(dir, dentry, &fname);
> + ext4_set_d_ops(dir, dentry);
> if (err == -ENOENT)
> return NULL;
> if (err)
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 1d82b56d9b11..ac593e9af270 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -4498,11 +4498,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> goto failed_mount4;
> }
>
> -#ifdef CONFIG_UNICODE
> - if (sbi->s_encoding)
> - sb->s_d_op = &ext4_dentry_ops;
> -#endif
> -
> sb->s_root = d_make_root(root);
> if (!sb->s_root) {
> ext4_msg(sb, KERN_ERR, "get root dentry failed");
> diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
> index 1a7bffe78ed5..0de461f2225a 100644
> --- a/include/linux/fscrypt.h
> +++ b/include/linux/fscrypt.h
> @@ -120,6 +120,8 @@ static inline struct page *fscrypt_pagecache_page(struct page *bounce_page)
>
> extern void fscrypt_free_bounce_page(struct page *bounce_page);
>
> +extern int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags);
> +
> /* policy.c */
> extern int fscrypt_ioctl_set_policy(struct file *, const void __user *);
> extern int fscrypt_ioctl_get_policy(struct file *, void __user *);

--
Gabriel Krisman Bertazi