Re: [PATCH v9 2/4] fs: Add standard casefolding support

Gabriel Krisman Bertazi
2020-06-24T05:33:46Z

Daniel Rosenberg <drosen@google.com> writes:

> This adds general supporting functions for filesystems that use
> utf8 casefolding. It provides standard dentry_operations and adds the
> necessary structures in struct super_block to allow this standardization.
>
> Ext4 and F2fs will switch to these common implementations.
>
> Signed-off-by: Daniel Rosenberg <drosen@google.com>
> ---
> fs/libfs.c | 101 +++++++++++++++++++++++++++++++++++++++++++++
> include/linux/fs.h | 22 ++++++++++
> 2 files changed, 123 insertions(+)
>
> diff --git a/fs/libfs.c b/fs/libfs.c
> index 4d08edf19c782..f7345a5ed562f 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -20,6 +20,8 @@
> #include <linux/fs_context.h>
> #include <linux/pseudo_fs.h>
> #include <linux/fsnotify.h>
> +#include <linux/unicode.h>
> +#include <linux/fscrypt.h>
>
> #include <linux/uaccess.h>
>
> @@ -1363,3 +1365,102 @@ bool is_empty_dir_inode(struct inode *inode)
> return (inode->i_fop == &empty_dir_operations) &&
> (inode->i_op == &empty_dir_inode_operations);
> }
> +
> +#ifdef CONFIG_UNICODE
> +/**
> + * needs_casefold - generic helper to determine if a filename should be casefolded
> + * @dir: Parent directory
> + *
> + * Generic helper for filesystems to use to determine if the name of a dentry
> + * should be casefolded. It does not make sense to casefold the no-key token of
> + * an encrypted filename.
> + *
> + * Return: if names will need casefolding
> + */
> +bool needs_casefold(const struct inode *dir)
> +{
> + return IS_CASEFOLDED(dir) && dir->i_sb->s_encoding &&
> + (!IS_ENCRYPTED(dir) || fscrypt_has_encryption_key(dir));
> +}
> +EXPORT_SYMBOL(needs_casefold);
> +
> +/**
> + * generic_ci_d_compare - generic d_compare implementation for casefolding filesystems
> + * @dentry: dentry whose name we are checking against
> + * @len: len of name of dentry
> + * @str: str pointer to name of dentry
> + * @name: Name to compare against
> + *
> + * Return: 0 if names match, 1 if mismatch, or -ERRNO
> + */
> +int generic_ci_d_compare(const struct dentry *dentry, unsigned int len,
> + const char *str, const struct qstr *name)
> +{
> + const struct dentry *parent = READ_ONCE(dentry->d_parent);
> + const struct inode *inode = READ_ONCE(parent->d_inode);
> + const struct super_block *sb = dentry->d_sb;
> + const struct unicode_map *um = sb->s_encoding;
> + struct qstr qstr = QSTR_INIT(str, len);
> + char strbuf[DNAME_INLINE_LEN];
> + int ret;
> +
> + if (!inode || !needs_casefold(inode))
> + goto fallback;
> + /*
> + * If the dentry name is stored in-line, then it may be concurrently
> + * modified by a rename. If this happens, the VFS will eventually retry
> + * the lookup, so it doesn't matter what ->d_compare() returns.
> + * However, it's unsafe to call utf8_strncasecmp() with an unstable
> + * string. Therefore, we have to copy the name into a temporary buffer.
> + */
> + if (len <= DNAME_INLINE_LEN - 1) {
> + memcpy(strbuf, str, len);
> + strbuf[len] = 0;
> + qstr.name = strbuf;
> + /* prevent compiler from optimizing out the temporary buffer */
> + barrier();
> + }
> + ret = utf8_strncasecmp(um, name, &qstr);
> + if (ret >= 0)
> + return ret;
> +
> + if (sb_has_enc_strict_mode(sb))
> + return -EINVAL;
> +fallback:
> + if (len != name->len)
> + return 1;
> + return !!memcmp(str, name->name, len);
> +}
> +EXPORT_SYMBOL(generic_ci_d_compare);
> +
> +/**
> + * generic_ci_d_hash - generic d_hash implementation for casefolding filesystems
> + * @dentry: dentry whose name we are hashing
> + * @str: qstr of name whose hash we should fill in
> + *
> + * Return: 0 if hash was successful, or -ERRNO
> + */
> +int generic_ci_d_hash(const struct dentry *dentry, struct qstr *str)
> +{
> + const struct inode *inode = READ_ONCE(dentry->d_inode);
> + struct super_block *sb = dentry->d_sb;
> + const struct unicode_map *um = sb->s_encoding;
> + int ret = 0;
> +
> + if (!inode || !needs_casefold(inode))
> + return 0;
> +
> + ret = utf8_casefold_hash(um, dentry, str);
> + if (ret < 0)
> + goto err;
> +
> + return 0;
> +err:
> + if (sb_has_enc_strict_mode(sb))
> + ret = -EINVAL;
> + else
> + ret = 0;
> + return ret;
> +}

Maybe drop the err label and simplify:

ret = utf8_casefold_hash(um, dentry, str);
if (ret < 0 && sb_has_enc_strict_mode(sb))
return -EINVAL;
return 0;

> +EXPORT_SYMBOL(generic_ci_d_hash);
> +#endif
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 3f881a892ea74..261904e06873b 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1392,6 +1392,12 @@ extern int send_sigurg(struct fown_struct *fown);
> #define SB_ACTIVE (1<<30)
> #define SB_NOUSER (1<<31)
>
> +/* These flags relate to encoding and casefolding */
> +#define SB_ENC_STRICT_MODE_FL (1 << 0)
> +
> +#define sb_has_enc_strict_mode(sb) \
> + (sb->s_encoding_flags & SB_ENC_STRICT_MODE_FL)
> +
> /*
> * Umount options
> */
> @@ -1461,6 +1467,10 @@ struct super_block {
> #endif
> #ifdef CONFIG_FS_VERITY
> const struct fsverity_operations *s_vop;
> +#endif
> +#ifdef CONFIG_UNICODE
> + struct unicode_map *s_encoding;
> + __u16 s_encoding_flags;
> #endif
> struct hlist_bl_head s_roots; /* alternate root dentries for NFS */
> struct list_head s_mounts; /* list of mounts; _not_ for fs use */
> @@ -3385,6 +3395,18 @@ extern int generic_file_fsync(struct file *, loff_t, loff_t, int);
>
> extern int generic_check_addressable(unsigned, u64);
>
> +#ifdef CONFIG_UNICODE
> +extern int generic_ci_d_hash(const struct dentry *dentry, struct qstr *str);
> +extern int generic_ci_d_compare(const struct dentry *dentry, unsigned int len,
> + const char *str, const struct qstr *name);
> +extern bool needs_casefold(const struct inode *dir);
> +#else
> +static inline bool needs_casefold(const struct inode *dir)
> +{
> + return 0;
> +}
> +#endif
> +
> #ifdef CONFIG_MIGRATION
> extern int buffer_migrate_page(struct address_space *,
> struct page *, struct page *,

--
Gabriel Krisman Bertazi