f2fs: check entire encrypted bigname when finding a dentry

If user has no key under an encrypted dir, fscrypt gives digested dentries.
Previously, when looking up a dentry, f2fs only checks its hash value with
first 4 bytes of the digested dentry, which didn't handle hash collisions fully.
This patch enhances to check entire dentry bytes likewise ext4.

Eric reported how to reproduce this issue by:

 # seq -f "edir/abcdefghijklmnopqrstuvwxyz012345%.0f" 100000 | xargs touch
 # find edir -type f | xargs stat -c %i | sort | uniq | wc -l
100000
 # sync
 # echo 3 > /proc/sys/vm/drop_caches
 # keyctl new_session
 # find edir -type f | xargs stat -c %i | sort | uniq | wc -l
99999

Cc: <stable@vger.kernel.org>
Reported-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
(fixed f2fs_dentry_hash() to work even when the hash is 0)
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/f2fs/dir.c

@@ -130,19 +130,29 @@ struct f2fs_dir_entry *find_target_dentry(struct fscrypt_name *fname,
 			continue;
 		}
 
-		/* encrypted case */
+		if (de->hash_code != namehash)
+			goto not_match;
+
 		de_name.name = d->filename[bit_pos];
 		de_name.len = le16_to_cpu(de->name_len);
 
-		/* show encrypted name */
-		if (fname->hash) {
-			if (de->hash_code == cpu_to_le32(fname->hash))
+#ifdef CONFIG_F2FS_FS_ENCRYPTION
+		if (unlikely(!name->name)) {
+			if (fname->usr_fname->name[0] == '_') {
+				if (de_name.len >= 16 &&
+					!memcmp(de_name.name + de_name.len - 16,
+						fname->crypto_buf.name + 8, 16))
 					goto found;
-		} else if (de_name.len == name->len &&
-			de->hash_code == namehash &&
+				goto not_match;
+			}
+			name->name = fname->crypto_buf.name;
+			name->len = fname->crypto_buf.len;
+		}
+#endif
+		if (de_name.len == name->len &&
 				!memcmp(de_name.name, name->name, name->len))
 			goto found;
-
+not_match:
 		if (max_slots && max_len > *max_slots)
 			*max_slots = max_len;
 		max_len = 0;
@@ -170,12 +180,7 @@ static struct f2fs_dir_entry *find_in_level(struct inode *dir,
 	struct f2fs_dir_entry *de = NULL;
 	bool room = false;
 	int max_slots;
-	f2fs_hash_t namehash;
-
-	if(fname->hash)
-		namehash = cpu_to_le32(fname->hash);
-	else
-		namehash = f2fs_dentry_hash(&name);
+	f2fs_hash_t namehash = f2fs_dentry_hash(&name, fname);
 
 	nbucket = dir_buckets(level, F2FS_I(dir)->i_dir_level);
 	nblock = bucket_blocks(level);
@@ -542,7 +547,7 @@ int f2fs_add_regular_entry(struct inode *dir, const struct qstr *new_name,
 
 	level = 0;
 	slots = GET_DENTRY_SLOTS(new_name->len);
-	dentry_hash = f2fs_dentry_hash(new_name);
+	dentry_hash = f2fs_dentry_hash(new_name, NULL);
 
 	current_depth = F2FS_I(dir)->i_current_depth;
 	if (F2FS_I(dir)->chash == dentry_hash) {

fs/f2fs/f2fs.h

@@ -2133,7 +2133,8 @@ int sanity_check_ckpt(struct f2fs_sb_info *sbi);
 /*
  * hash.c
  */
-f2fs_hash_t f2fs_dentry_hash(const struct qstr *name_info);
+f2fs_hash_t f2fs_dentry_hash(const struct qstr *name_info,
+				struct fscrypt_name *fname);
 
 /*
  * node.c

fs/f2fs/hash.c

@@ -70,7 +70,8 @@ static void str2hashbuf(const unsigned char *msg, size_t len,
 		*buf++ = pad;
 }
 
-f2fs_hash_t f2fs_dentry_hash(const struct qstr *name_info)
+f2fs_hash_t f2fs_dentry_hash(const struct qstr *name_info,
+				struct fscrypt_name *fname)
 {
 	__u32 hash;
 	f2fs_hash_t f2fs_hash;
@@ -79,6 +80,10 @@ f2fs_hash_t f2fs_dentry_hash(const struct qstr *name_info)
 	const unsigned char *name = name_info->name;
 	size_t len = name_info->len;
 
+	/* encrypted bigname case */
+	if (fname && !fname->disk_name.name)
+		return cpu_to_le32(fname->hash);
+
 	if (is_dot_dotdot(name_info))
 		return 0;
 

fs/f2fs/inline.c

@@ -296,7 +296,7 @@ struct f2fs_dir_entry *find_in_inline_dir(struct inode *dir,
 		return NULL;
 	}
 
-	namehash = f2fs_dentry_hash(&name);
+	namehash = f2fs_dentry_hash(&name, fname);
 
 	inline_dentry = inline_data_addr(ipage);
 
@@ -533,7 +533,7 @@ int f2fs_add_inline_entry(struct inode *dir, const struct qstr *new_name,
 
 	f2fs_wait_on_page_writeback(ipage, NODE, true);
 
-	name_hash = f2fs_dentry_hash(new_name);
+	name_hash = f2fs_dentry_hash(new_name, NULL);
 	make_dentry_ptr(NULL, &d, (void *)dentry_blk, 2);
 	f2fs_update_dentry(ino, mode, &d, new_name, name_hash, bit_pos);