On Mon, Sep 24, 2018 at 05:56:50PM -0400, Gabriel Krisman Bertazi wrote:
> Support for encoding is considered an incompatible feature, since it has
> potential to create collisions of file names in existing filesystems.
> If the feature flag is not enabled, the entire filesystem will operate
> on opaque byte sequences, respecting the original behavior.
>
> The charset data is encoded in a new field in the superblock using a
> magic number specific to ext4. This is the easiest way I found to avoid
> writing the name of the charset in the superblock. The magic number is
> mapped to the exact NLS table, but the mapping is specific to ext4.
> Since we don't have any commitment to support old encodings, the only
> encodings I am supporting right now is utf8n-10.0.0 and ascii, both
> using the NLS abstraction.
>
> The current implementation prevents the user from enabling encoding and
> per-directory encryption on the same filesystem at the same time. The
> incompatibility between these features lies in how we do efficient
> directory searches when we cannot be sure the encryption of the user
> provided fname will match the actual hash stored in the disk without
> decrypting every directory entry, because of normalization cases. My
> quickest solution is to simply block the concurrent use of these
> features for now, and enable it later, once we have a better solution.
>
> Changes since v1:
> - Guard code with CONFIG_NLS.
> - Use 16 bits for s_ioencoding.
> - Split mount option from this patch
>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxxxx>
> ---
> fs/ext4/ext4.h | 19 ++++++++++++-
> fs/ext4/super.c | 73 +++++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 91 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index ac05bd86643a..6bdaba9c6923 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1190,6 +1190,11 @@ extern void ext4_set_bits(void *bm, int cur, int len);
> /* Metadata checksum algorithm codes */
> #define EXT4_CRC32C_CHKSUM 1
>
> +/* Be careful when modifying these flags. The lower byte must match the
> + * NLS flags. */
> +
> +#define EXT4_ENC_NLS_FL_MASK 0x00FF
> +
> /*
> * Structure of the super block
> */
> @@ -1316,7 +1321,9 @@ struct ext4_super_block {
> __u8 s_first_error_time_hi;
> __u8 s_last_error_time_hi;
> __u8 s_pad[2];
> - __le32 s_reserved[96]; /* Padding to the end of the block */
> + __le16 s_ioencoding; /* charset encoding */
> + __le16 s_ioencoding_flags; /* charset encoding flags */
> + __le32 s_reserved[95]; /* Padding to the end of the block */
Please update Documentation/filesystems/ext4/super.rst with this when it
appears after the merge window.
> __le32 s_checksum; /* crc32c(superblock) */
> };
>
> @@ -1341,6 +1348,8 @@ struct ext4_super_block {
> /* Number of quota types we support */
> #define EXT4_MAXQUOTAS 3
>
> +struct ext4_sb_encodings;
> +
> /*
> * fourth extended-fs super-block data in memory
> */
> @@ -1390,6 +1399,11 @@ struct ext4_sb_info {
> struct kobject s_kobj;
> struct completion s_kobj_unregister;
> struct super_block *s_sb;
> +#ifdef CONFIG_NLS
> + const struct ext4_sb_encodings *encoding_info;
> + struct nls_table *encoding;
> + __u16 encoding_flags;
> +#endif
>
> /* Journaling */
> struct journal_s *s_journal;
> @@ -1665,6 +1679,7 @@ static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
> #define EXT4_FEATURE_INCOMPAT_LARGEDIR 0x4000 /* >2GB or 3-lvl htree */
> #define EXT4_FEATURE_INCOMPAT_INLINE_DATA 0x8000 /* data in inode */
> #define EXT4_FEATURE_INCOMPAT_ENCRYPT 0x10000
> +#define EXT4_FEATURE_INCOMPAT_IOENCODING 0x20000
/me wonders how the 'ioencoding' name came about? We're not encoding
disk IO, just directory entries.
>
> #define EXT4_FEATURE_COMPAT_FUNCS(name, flagname) \
> static inline bool ext4_has_feature_##name(struct super_block *sb) \
> @@ -1753,6 +1768,7 @@ EXT4_FEATURE_INCOMPAT_FUNCS(csum_seed, CSUM_SEED)
> EXT4_FEATURE_INCOMPAT_FUNCS(largedir, LARGEDIR)
> EXT4_FEATURE_INCOMPAT_FUNCS(inline_data, INLINE_DATA)
> EXT4_FEATURE_INCOMPAT_FUNCS(encrypt, ENCRYPT)
> +EXT4_FEATURE_INCOMPAT_FUNCS(ioencoding, IOENCODING)
>
> #define EXT2_FEATURE_COMPAT_SUPP EXT4_FEATURE_COMPAT_EXT_ATTR
> #define EXT2_FEATURE_INCOMPAT_SUPP (EXT4_FEATURE_INCOMPAT_FILETYPE| \
> @@ -1780,6 +1796,7 @@ EXT4_FEATURE_INCOMPAT_FUNCS(encrypt, ENCRYPT)
> EXT4_FEATURE_INCOMPAT_MMP | \
> EXT4_FEATURE_INCOMPAT_INLINE_DATA | \
> EXT4_FEATURE_INCOMPAT_ENCRYPT | \
> + EXT4_FEATURE_INCOMPAT_IOENCODING | \
> EXT4_FEATURE_INCOMPAT_CSUM_SEED | \
> EXT4_FEATURE_INCOMPAT_LARGEDIR)
> #define EXT4_FEATURE_RO_COMPAT_SUPP (EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER| \
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index a430fb3e9720..ccf4742fea3b 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -42,6 +42,7 @@
> #include <linux/cleancache.h>
> #include <linux/uaccess.h>
> #include <linux/iversion.h>
> +#include <linux/nls.h>
>
> #include <linux/kthread.h>
> #include <linux/freezer.h>
> @@ -1010,6 +1011,10 @@ static void ext4_put_super(struct super_block *sb)
> crypto_free_shash(sbi->s_chksum_driver);
> kfree(sbi->s_blockgroup_lock);
> fs_put_dax(sbi->s_daxdev);
> +#ifdef CONFIG_NLS
> + unload_nls(sbi->encoding);
> + kfree(sbi->encoding_info);
> +#endif
> kfree(sbi);
> }
>
> @@ -1703,6 +1708,31 @@ static const struct mount_opts {
> {Opt_err, 0, 0}
> };
>
> +#ifdef CONFIG_NLS
> +static const struct ext4_sb_encodings {
> + char *name;
> + char *version;
> +} ext4_sb_encoding_map[] = {
> + /* 0x0 */ {"ascii", NULL},
> + /* 0x1 */ {"utf8", "10.0.0"},
> +};
> +
> +static int
> +ext4_sb_read_encoding(const struct ext4_super_block *es,
> + const struct ext4_sb_encodings **encoding, __u16 *flags)
> +{
> + __u16 magic = le16_to_cpu(es->s_ioencoding);
> +
> + if (magic >= ARRAY_SIZE(ext4_sb_encoding_map))
> + return -EINVAL;
> +
> + *encoding = &ext4_sb_encoding_map[magic];
> + *flags = le16_to_cpu(es->s_ioencoding_flags);
> +
> + return 0;
> +}
> +#endif
> +
> static int handle_mount_opt(struct super_block *sb, char *opt, int token,
> substring_t *args, unsigned long *journal_devnum,
> unsigned int *journal_ioprio, int is_remount)
> @@ -3515,6 +3545,11 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> int err = 0;
> unsigned int journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
> ext4_group_t first_not_zeroed;
> +#ifdef CONFIG_NLS
> + struct nls_table *encoding;
> + const struct ext4_sb_encodings *encoding_info;
> + __u16 nls_flags;
> +#endif
>
> if ((data && !orig_data) || !sbi)
> goto out_free_base;
> @@ -3687,6 +3722,39 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> &journal_ioprio, 0))
> goto failed_mount;
>
> +#ifdef CONFIG_NLS
> + if (ext4_has_feature_ioencoding(sb) && !sbi->encoding) {
> + if (ext4_has_feature_encrypt(sb)) {
> + ext4_msg(sb, KERN_ERR,
> + "Can't mount with both encoding and encryption");
> + goto failed_mount;
> + }
> +
> + if (ext4_sb_read_encoding(es, &encoding_info, &nls_flags)) {
> + ext4_msg(sb, KERN_ERR,
> + "Encoding requested by superblock is unknown");
> + goto failed_mount;
> + }
> +
> + encoding = load_nls_version(encoding_info->name,
> + encoding_info->version,
> + nls_flags & EXT4_ENC_NLS_FL_MASK);
> + if (IS_ERR(encoding)) {
> + ext4_msg(sb, KERN_ERR, "can't mount with superblock charset: "
> + "%s-%s not supported by the kernel. flags: 0x%x",
> + encoding_info->name, encoding_info->version,
> + nls_flags);
> + goto failed_mount;
> + }
> + ext4_msg(sb, KERN_INFO,"Using encoding defined by superblock: "
> + "%s-%s with flags 0x%hx", encoding_info->name,
> + encoding_info->version?:"\b", nls_flags);
> +
> + sbi->encoding = encoding;
> + sbi->encoding_flags = nls_flags;
> + }
> +#endif
> +
> if (test_opt(sb, DATA_FLAGS) == EXT4_MOUNT_JOURNAL_DATA) {
> printk_once(KERN_WARNING "EXT4-fs: Warning: mounting "
> "with data=journal disables delayed "
> @@ -4527,6 +4595,11 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> failed_mount:
> if (sbi->s_chksum_driver)
> crypto_free_shash(sbi->s_chksum_driver);
> +
> +#ifdef CONFIG_NLS
> + unload_nls(sbi->encoding);
> +#endif
> +
> #ifdef CONFIG_QUOTA
> for (i = 0; i < EXT4_MAXQUOTAS; i++)
> kfree(sbi->s_qf_names[i]);
> --
> 2.19.0
>
