ext4: handle casefolding with encryption

This adds support for encryption with casefolding.

Since the name on disk is case preserving, and also encrypted, we can no
longer just recompute the hash on the fly. Additionally, to avoid
leaking extra information from the hash of the unencrypted name, we use
siphash via an fscrypt v2 policy.

The hash is stored at the end of the directory entry for all entries
inside of an encrypted and casefolded directory apart from those that
deal with '.' and '..'. This way, the change is backwards compatible
with existing ext4 filesystems.

[ Changed to advertise this feature via the file:
  /sys/fs/ext4/features/encrypted_casefold -- TYT ]

Signed-off-by: Daniel Rosenberg <drosen@google.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Link: https://lore.kernel.org/r/20210319073414.1381041-2-drosen@google.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 146 insertions, 52 deletions

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 883e2a7cd4ab..68646500f7ba 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -280,9 +280,11 @@ static int dx_make_map(struct inode *dir, struct ext4_dir_entry_2 *de,
 		       unsigned blocksize, struct dx_hash_info *hinfo,
 		       struct dx_map_entry map[]);
 static void dx_sort_map(struct dx_map_entry *map, unsigned count);
-static struct ext4_dir_entry_2 *dx_move_dirents(char *from, char *to,
-		struct dx_map_entry *offsets, int count, unsigned blocksize);
-static struct ext4_dir_entry_2* dx_pack_dirents(char *base, unsigned blocksize);
+static struct ext4_dir_entry_2 *dx_move_dirents(struct inode *dir, char *from,
+					char *to, struct dx_map_entry *offsets,
+					int count, unsigned int blocksize);
+static struct ext4_dir_entry_2 *dx_pack_dirents(struct inode *dir, char *base,
+						unsigned int blocksize);
 static void dx_insert_block(struct dx_frame *frame,
 					u32 hash, ext4_lblk_t block);
 static int ext4_htree_next_block(struct inode *dir, __u32 hash,
@@ -574,8 +576,9 @@ static inline void dx_set_limit(struct dx_entry *entries, unsigned value)
 
 static inline unsigned dx_root_limit(struct inode *dir, unsigned infosize)
 {
-	unsigned entry_space = dir->i_sb->s_blocksize - EXT4_DIR_REC_LEN(1) -
-		EXT4_DIR_REC_LEN(2) - infosize;
+	unsigned int entry_space = dir->i_sb->s_blocksize -
+			ext4_dir_rec_len(1, NULL) -
+			ext4_dir_rec_len(2, NULL) - infosize;
 
 	if (ext4_has_metadata_csum(dir->i_sb))
 		entry_space -= sizeof(struct dx_tail);
@@ -584,7 +587,8 @@ static inline unsigned dx_root_limit(struct inode *dir, unsigned infosize)
 
 static inline unsigned dx_node_limit(struct inode *dir)
 {
-	unsigned entry_space = dir->i_sb->s_blocksize - EXT4_DIR_REC_LEN(0);
+	unsigned int entry_space = dir->i_sb->s_blocksize -
+			ext4_dir_rec_len(0, dir);
 
 	if (ext4_has_metadata_csum(dir->i_sb))
 		entry_space -= sizeof(struct dx_tail);
@@ -673,7 +677,10 @@ static struct stats dx_show_leaf(struct inode *dir,
 						name = fname_crypto_str.name;
 						len = fname_crypto_str.len;
 					}
-					ext4fs_dirhash(dir, de->name,
+					if (IS_CASEFOLDED(dir))
+						h.hash = EXT4_DIRENT_HASH(de);
+					else
+						ext4fs_dirhash(dir, de->name,
 						       de->name_len, &h);
 					printk("%*.s:(E)%x.%u ", len, name,
 					       h.hash, (unsigned) ((char *) de
@@ -689,7 +696,7 @@ static struct stats dx_show_leaf(struct inode *dir,
 				       (unsigned) ((char *) de - base));
 #endif
 			}
-			space += EXT4_DIR_REC_LEN(de->name_len);
+			space += ext4_dir_rec_len(de->name_len, dir);
 			names++;
 		}
 		de = ext4_next_entry(de, size);
@@ -784,11 +791,25 @@ dx_probe(struct ext4_filename *fname, struct inode *dir,
 	root = (struct dx_root *) frame->bh->b_data;
 	if (root->info.hash_version != DX_HASH_TEA &&
 	    root->info.hash_version != DX_HASH_HALF_MD4 &&
-	    root->info.hash_version != DX_HASH_LEGACY) {
+	    root->info.hash_version != DX_HASH_LEGACY &&
+	    root->info.hash_version != DX_HASH_SIPHASH) {
 		ext4_warning_inode(dir, "Unrecognised inode hash code %u",
 				   root->info.hash_version);
 		goto fail;
 	}
+	if (ext4_hash_in_dirent(dir)) {
+		if (root->info.hash_version != DX_HASH_SIPHASH) {
+			ext4_warning_inode(dir,
+				"Hash in dirent, but hash is not SIPHASH");
+			goto fail;
+		}
+	} else {
+		if (root->info.hash_version == DX_HASH_SIPHASH) {
+			ext4_warning_inode(dir,
+				"Hash code is SIPHASH, but hash not in dirent");
+			goto fail;
+		}
+	}
 	if (fname)
 		hinfo = &fname->hinfo;
 	hinfo->hash_version = root->info.hash_version;
@@ -997,6 +1018,7 @@ static int htree_dirblock_to_tree(struct file *dir_file,
 	struct ext4_dir_entry_2 *de, *top;
 	int err = 0, count = 0;
 	struct fscrypt_str fname_crypto_str = FSTR_INIT(NULL, 0), tmp_str;
+	int csum = ext4_has_metadata_csum(dir->i_sb);
 
 	dxtrace(printk(KERN_INFO "In htree dirblock_to_tree: block %lu\n",
 							(unsigned long)block));
@@ -1005,9 +1027,11 @@ static int htree_dirblock_to_tree(struct file *dir_file,
 		return PTR_ERR(bh);
 
 	de = (struct ext4_dir_entry_2 *) bh->b_data;
+	/* csum entries are not larger in the casefolded encrypted case */
 	top = (struct ext4_dir_entry_2 *) ((char *) de +
 					   dir->i_sb->s_blocksize -
-					   EXT4_DIR_REC_LEN(0));
+					   ext4_dir_rec_len(0,
+							   csum ? NULL : dir));
 	/* Check if the directory is encrypted */
 	if (IS_ENCRYPTED(dir)) {
 		err = fscrypt_prepare_readdir(dir);
@@ -1031,7 +1055,17 @@ static int htree_dirblock_to_tree(struct file *dir_file,
 			/* silently ignore the rest of the block */
 			break;
 		}
-		ext4fs_dirhash(dir, de->name, de->name_len, hinfo);
+		if (ext4_hash_in_dirent(dir)) {
+			if (de->name_len && de->inode) {
+				hinfo->hash = EXT4_DIRENT_HASH(de);
+				hinfo->minor_hash = EXT4_DIRENT_MINOR_HASH(de);
+			} else {
+				hinfo->hash = 0;
+				hinfo->minor_hash = 0;
+			}
+		} else {
+			ext4fs_dirhash(dir, de->name, de->name_len, hinfo);
+		}
 		if ((hinfo->hash < start_hash) ||
 		    ((hinfo->hash == start_hash) &&
 		     (hinfo->minor_hash < start_minor_hash)))
@@ -1100,7 +1134,11 @@ int ext4_htree_fill_tree(struct file *dir_file, __u32 start_hash,
 		       start_hash, start_minor_hash));
 	dir = file_inode(dir_file);
 	if (!(ext4_test_inode_flag(dir, EXT4_INODE_INDEX))) {
-		hinfo.hash_version = EXT4_SB(dir->i_sb)->s_def_hash_version;
+		if (ext4_hash_in_dirent(dir))
+			hinfo.hash_version = DX_HASH_SIPHASH;
+		else
+			hinfo.hash_version =
+					EXT4_SB(dir->i_sb)->s_def_hash_version;
 		if (hinfo.hash_version <= DX_HASH_TEA)
 			hinfo.hash_version +=
 				EXT4_SB(dir->i_sb)->s_hash_unsigned;
@@ -1218,7 +1256,10 @@ static int dx_make_map(struct inode *dir, struct ext4_dir_entry_2 *de,
 
 	while ((char *) de < base + blocksize) {
 		if (de->name_len && de->inode) {
-			ext4fs_dirhash(dir, de->name, de->name_len, &h);
+			if (ext4_hash_in_dirent(dir))
+				h.hash = EXT4_DIRENT_HASH(de);
+			else
+				ext4fs_dirhash(dir, de->name, de->name_len, &h);
 			map_tail--;
 			map_tail->hash = h.hash;
 			map_tail->offs = ((char *) de - base)>>2;
@@ -1282,31 +1323,47 @@ static void dx_insert_block(struct dx_frame *frame, u32 hash, ext4_lblk_t block)
  * Returns: 0 if the directory entry matches, more than 0 if it
  * doesn't match or less than zero on error.
  */
-int ext4_ci_compare(const struct inode *parent, const struct qstr *name,
-		    const struct qstr *entry, bool quick)
+static int ext4_ci_compare(const struct inode *parent, const struct qstr *name,
+			   u8 *de_name, size_t de_name_len, bool quick)
 {
 	const struct super_block *sb = parent->i_sb;
 	const struct unicode_map *um = sb->s_encoding;
+	struct fscrypt_str decrypted_name = FSTR_INIT(NULL, de_name_len);
+	struct qstr entry = QSTR_INIT(de_name, de_name_len);
 	int ret;
 
+	if (IS_ENCRYPTED(parent)) {
+		const struct fscrypt_str encrypted_name =
+				FSTR_INIT(de_name, de_name_len);
+
+		decrypted_name.name = kmalloc(de_name_len, GFP_KERNEL);
+		if (!decrypted_name.name)
+			return -ENOMEM;
+		ret = fscrypt_fname_disk_to_usr(parent, 0, 0, &encrypted_name,
+						&decrypted_name);
+		if (ret < 0)
+			goto out;
+		entry.name = decrypted_name.name;
+		entry.len = decrypted_name.len;
+	}
+
 	if (quick)
-		ret = utf8_strncasecmp_folded(um, name, entry);
+		ret = utf8_strncasecmp_folded(um, name, &entry);
 	else
-		ret = utf8_strncasecmp(um, name, entry);
-
+		ret = utf8_strncasecmp(um, name, &entry);
 	if (ret < 0) {
 		/* Handle invalid character sequence as either an error
 		 * or as an opaque byte sequence.
 		 */
 		if (sb_has_strict_encoding(sb))
-			return -EINVAL;
-
-		if (name->len != entry->len)
-			return 1;
-
-		return !!memcmp(name->name, entry->name, name->len);
+			ret = -EINVAL;
+		else if (name->len != entry.len)
+			ret = 1;
+		else
+			ret = !!memcmp(name->name, entry.name, entry.len);
 	}
-
+out:
+	kfree(decrypted_name.name);
 	return ret;
 }
 
@@ -1342,14 +1399,11 @@ void ext4_fname_setup_ci_filename(struct inode *dir, const struct qstr *iname,
  *
  * Return: %true if the directory entry matches, otherwise %false.
  */
-static inline bool ext4_match(const struct inode *parent,
+static bool ext4_match(struct inode *parent,
 			      const struct ext4_filename *fname,
-			      const struct ext4_dir_entry_2 *de)
+			      struct ext4_dir_entry_2 *de)
 {
 	struct fscrypt_name f;
-#ifdef CONFIG_UNICODE
-	const struct qstr entry = {.name = de->name, .len = de->name_len};
-#endif
 
 	if (!de->inode)
 		return false;
@@ -1365,10 +1419,23 @@ static inline bool ext4_match(const struct inode *parent,
 		if (fname->cf_name.name) {
 			struct qstr cf = {.name = fname->cf_name.name,
 					  .len = fname->cf_name.len};
-			return !ext4_ci_compare(parent, &cf, &entry, true);
+			if (IS_ENCRYPTED(parent)) {
+				struct dx_hash_info hinfo;
+
+				hinfo.hash_version = DX_HASH_SIPHASH;
+				hinfo.seed = NULL;
+				ext4fs_dirhash(parent, fname->cf_name.name,
+						fname_len(fname), &hinfo);
+				if (hinfo.hash != EXT4_DIRENT_HASH(de) ||
+						hinfo.minor_hash !=
+						    EXT4_DIRENT_MINOR_HASH(de))
+					return 0;
+			}
+			return !ext4_ci_compare(parent, &cf, de->name,
+							de->name_len, true);
 		}
-		return !ext4_ci_compare(parent, fname->usr_fname, &entry,
-					false);
+		return !ext4_ci_compare(parent, fname->usr_fname, de->name,
+						de->name_len, false);
 	}
 #endif
 
@@ -1765,7 +1832,8 @@ struct dentry *ext4_get_parent(struct dentry *child)
  * Returns pointer to last entry moved.
  */
 static struct ext4_dir_entry_2 *
-dx_move_dirents(char *from, char *to, struct dx_map_entry *map, int count,
+dx_move_dirents(struct inode *dir, char *from, char *to,
+		struct dx_map_entry *map, int count,
 		unsigned blocksize)
 {
 	unsigned rec_len = 0;
@@ -1773,7 +1841,8 @@ dx_move_dirents(char *from, char *to, struct dx_map_entry *map, int count,
 	while (count--) {
 		struct ext4_dir_entry_2 *de = (struct ext4_dir_entry_2 *)
 						(from + (map->offs<<2));
-		rec_len = EXT4_DIR_REC_LEN(de->name_len);
+		rec_len = ext4_dir_rec_len(de->name_len, dir);
+
 		memcpy (to, de, rec_len);
 		((struct ext4_dir_entry_2 *) to)->rec_len =
 				ext4_rec_len_to_disk(rec_len, blocksize);
@@ -1788,7 +1857,8 @@ dx_move_dirents(char *from, char *to, struct dx_map_entry *map, int count,
  * Compact each dir entry in the range to the minimal rec_len.
  * Returns pointer to last entry in range.
  */
-static struct ext4_dir_entry_2* dx_pack_dirents(char *base, unsigned blocksize)
+static struct ext4_dir_entry_2 *dx_pack_dirents(struct inode *dir, char *base,
+							unsigned int blocksize)
 {
 	struct ext4_dir_entry_2 *next, *to, *prev, *de = (struct ext4_dir_entry_2 *) base;
 	unsigned rec_len = 0;
@@ -1797,7 +1867,7 @@ static struct ext4_dir_entry_2* dx_pack_dirents(char *base, unsigned blocksize)
 	while ((char*)de < base + blocksize) {
 		next = ext4_next_entry(de, blocksize);
 		if (de->inode && de->name_len) {
-			rec_len = EXT4_DIR_REC_LEN(de->name_len);
+			rec_len = ext4_dir_rec_len(de->name_len, dir);
 			if (de > to)
 				memmove(to, de, rec_len);
 			to->rec_len = ext4_rec_len_to_disk(rec_len, blocksize);
@@ -1887,9 +1957,9 @@ static struct ext4_dir_entry_2 *do_split(handle_t *handle, struct inode *dir,
 					hash2, split, count-split));
 
 	/* Fancy dance to stay within two buffers */
-	de2 = dx_move_dirents(data1, data2, map + split, count - split,
+	de2 = dx_move_dirents(dir, data1, data2, map + split, count - split,
 			      blocksize);
-	de = dx_pack_dirents(data1, blocksize);
+	de = dx_pack_dirents(dir, data1, blocksize);
 	de->rec_len = ext4_rec_len_to_disk(data1 + (blocksize - csum_size) -
 					   (char *) de,
 					   blocksize);
@@ -1937,7 +2007,7 @@ int ext4_find_dest_de(struct inode *dir, struct inode *inode,
 		      struct ext4_dir_entry_2 **dest_de)
 {
 	struct ext4_dir_entry_2 *de;
-	unsigned short reclen = EXT4_DIR_REC_LEN(fname_len(fname));
+	unsigned short reclen = ext4_dir_rec_len(fname_len(fname), dir);
 	int nlen, rlen;
 	unsigned int offset = 0;
 	char *top;
@@ -1950,7 +2020,7 @@ int ext4_find_dest_de(struct inode *dir, struct inode *inode,
 			return -EFSCORRUPTED;
 		if (ext4_match(dir, fname, de))
 			return -EEXIST;
-		nlen = EXT4_DIR_REC_LEN(de->name_len);
+		nlen = ext4_dir_rec_len(de->name_len, dir);
 		rlen = ext4_rec_len_from_disk(de->rec_len, buf_size);
 		if ((de->inode ? rlen - nlen : rlen) >= reclen)
 			break;
@@ -1964,7 +2034,8 @@ int ext4_find_dest_de(struct inode *dir, struct inode *inode,
 	return 0;
 }
 
-void ext4_insert_dentry(struct inode *inode,
+void ext4_insert_dentry(struct inode *dir,
+			struct inode *inode,
 			struct ext4_dir_entry_2 *de,
 			int buf_size,
 			struct ext4_filename *fname)
@@ -1972,7 +2043,7 @@ void ext4_insert_dentry(struct inode *inode,
 
 	int nlen, rlen;
 
-	nlen = EXT4_DIR_REC_LEN(de->name_len);
+	nlen = ext4_dir_rec_len(de->name_len, dir);
 	rlen = ext4_rec_len_from_disk(de->rec_len, buf_size);
 	if (de->inode) {
 		struct ext4_dir_entry_2 *de1 =
@@ -1986,6 +2057,17 @@ void ext4_insert_dentry(struct inode *inode,
 	ext4_set_de_type(inode->i_sb, de, inode->i_mode);
 	de->name_len = fname_len(fname);
 	memcpy(de->name, fname_name(fname), fname_len(fname));
+	if (ext4_hash_in_dirent(dir)) {
+		struct dx_hash_info hinfo;
+
+		hinfo.hash_version = DX_HASH_SIPHASH;
+		hinfo.seed = NULL;
+		ext4fs_dirhash(dir, fname_usr_name(fname),
+				fname_len(fname), &hinfo);
+		EXT4_DIRENT_HASHES(de)->hash = cpu_to_le32(hinfo.hash);
+		EXT4_DIRENT_HASHES(de)->minor_hash =
+				cpu_to_le32(hinfo.minor_hash);
+	}
 }
 
 /*
@@ -2022,7 +2104,7 @@ static int add_dirent_to_buf(handle_t *handle, struct ext4_filename *fname,
 	}
 
 	/* By now the buffer is marked for journaling */
-	ext4_insert_dentry(inode, de, blocksize, fname);
+	ext4_insert_dentry(dir, inode, de, blocksize, fname);
 
 	/*
 	 * XXX shouldn't update any times until successful
@@ -2114,11 +2196,16 @@ static int make_indexed_dir(handle_t *handle, struct ext4_filename *fname,
 
 	/* Initialize the root; the dot dirents already exist */
 	de = (struct ext4_dir_entry_2 *) (&root->dotdot);
-	de->rec_len = ext4_rec_len_to_disk(blocksize - EXT4_DIR_REC_LEN(2),
-					   blocksize);
+	de->rec_len = ext4_rec_len_to_disk(
+			blocksize - ext4_dir_rec_len(2, NULL), blocksize);
 	memset (&root->info, 0, sizeof(root->info));
 	root->info.info_length = sizeof(root->info);
-	root->info.hash_version = EXT4_SB(dir->i_sb)->s_def_hash_version;
+	if (ext4_hash_in_dirent(dir))
+		root->info.hash_version = DX_HASH_SIPHASH;
+	else
+		root->info.hash_version =
+				EXT4_SB(dir->i_sb)->s_def_hash_version;
+
 	entries = root->entries;
 	dx_set_block(entries, 1);
 	dx_set_count(entries, 1);
@@ -2129,7 +2216,12 @@ static int make_indexed_dir(handle_t *handle, struct ext4_filename *fname,
 	if (fname->hinfo.hash_version <= DX_HASH_TEA)
 		fname->hinfo.hash_version += EXT4_SB(dir->i_sb)->s_hash_unsigned;
 	fname->hinfo.seed = EXT4_SB(dir->i_sb)->s_hash_seed;
-	ext4fs_dirhash(dir, fname_name(fname), fname_len(fname), &fname->hinfo);
+	if (ext4_hash_in_dirent(dir))
+		ext4fs_dirhash(dir, fname_usr_name(fname),
+				fname_len(fname), &fname->hinfo);
+	else
+		ext4fs_dirhash(dir, fname_name(fname),
+				fname_len(fname), &fname->hinfo);
 
 	memset(frames, 0, sizeof(frames));
 	frame = frames;
@@ -2722,7 +2814,7 @@ struct ext4_dir_entry_2 *ext4_init_dot_dotdot(struct inode *inode,
 {
 	de->inode = cpu_to_le32(inode->i_ino);
 	de->name_len = 1;
-	de->rec_len = ext4_rec_len_to_disk(EXT4_DIR_REC_LEN(de->name_len),
+	de->rec_len = ext4_rec_len_to_disk(ext4_dir_rec_len(de->name_len, NULL),
 					   blocksize);
 	strcpy(de->name, ".");
 	ext4_set_de_type(inode->i_sb, de, S_IFDIR);
@@ -2732,11 +2824,12 @@ struct ext4_dir_entry_2 *ext4_init_dot_dotdot(struct inode *inode,
 	de->name_len = 2;
 	if (!dotdot_real_len)
 		de->rec_len = ext4_rec_len_to_disk(blocksize -
-					(csum_size + EXT4_DIR_REC_LEN(1)),
+					(csum_size + ext4_dir_rec_len(1, NULL)),
 					blocksize);
 	else
 		de->rec_len = ext4_rec_len_to_disk(
-				EXT4_DIR_REC_LEN(de->name_len), blocksize);
+					ext4_dir_rec_len(de->name_len, NULL),
+					blocksize);
 	strcpy(de->name, "..");
 	ext4_set_de_type(inode->i_sb, de, S_IFDIR);
 
@@ -2869,7 +2962,8 @@ bool ext4_empty_dir(struct inode *inode)
 	}
 
 	sb = inode->i_sb;
-	if (inode->i_size < EXT4_DIR_REC_LEN(1) + EXT4_DIR_REC_LEN(2)) {
+	if (inode->i_size < ext4_dir_rec_len(1, NULL) +
+					ext4_dir_rec_len(2, NULL)) {
 		EXT4_ERROR_INODE(inode, "invalid size");
 		return true;
 	}