hfsplus: Verify inode mode when loading from disk

syzbot is reporting that S_IFMT bits of inode->i_mode can become bogus when
the S_IFMT bits of the 16bits "mode" field loaded from disk are corrupted.

According to [1], the permissions field was treated as reserved in Mac OS
8 and 9. According to [2], the reserved field was explicitly initialized
with 0, and that field must remain 0 as long as reserved. Therefore, when
the "mode" field is not 0 (i.e. no longer reserved), the file must be
S_IFDIR if dir == 1, and the file must be one of S_IFREG/S_IFLNK/S_IFCHR/
S_IFBLK/S_IFIFO/S_IFSOCK if dir == 0.

Reported-by: syzbot <syzbot+895c23f6917da440ed0d@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=895c23f6917da440ed0d
Link: https://developer.apple.com/library/archive/technotes/tn/tn1150.html#HFSPlusPermissions [1]
Link: https://developer.apple.com/library/archive/technotes/tn/tn1150.html#ReservedAndPadFields [2]
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>
Link: https://lore.kernel.org/r/04ded9f9-73fb-496c-bfa5-89c4f5d1d7bb@I-love.SAKURA.ne.jp
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>

Author: Tetsuo Handa

fs/hfsplus/inode.c

@@ -180,13 +180,29 @@ const struct dentry_operations hfsplus_dentry_operations = {
 	.d_compare    = hfsplus_compare_dentry,
 };
 
-static void hfsplus_get_perms(struct inode *inode,
-		struct hfsplus_perm *perms, int dir)
+static int hfsplus_get_perms(struct inode *inode,
+			     struct hfsplus_perm *perms, int dir)
 {
 	struct hfsplus_sb_info *sbi = HFSPLUS_SB(inode->i_sb);
 	u16 mode;
 
 	mode = be16_to_cpu(perms->mode);
+	if (dir) {
+		if (mode && !S_ISDIR(mode))
+			goto bad_type;
+	} else if (mode) {
+		switch (mode & S_IFMT) {
+		case S_IFREG:
+		case S_IFLNK:
+		case S_IFCHR:
+		case S_IFBLK:
+		case S_IFIFO:
+		case S_IFSOCK:
+			break;
+		default:
+			goto bad_type;
+		}
+	}
 
 	i_uid_write(inode, be32_to_cpu(perms->owner));
 	if ((test_bit(HFSPLUS_SB_UID, &sbi->flags)) || (!i_uid_read(inode) && !mode))
@@ -212,6 +228,10 @@ static void hfsplus_get_perms(struct inode *inode,
 		inode->i_flags |= S_APPEND;
 	else
 		inode->i_flags &= ~S_APPEND;
+	return 0;
+bad_type:
+	pr_err("invalid file type 0%04o for inode %lu\n", mode, inode->i_ino);
+	return -EIO;
 }
 
 static int hfsplus_file_open(struct inode *inode, struct file *file)
@@ -516,7 +536,9 @@ int hfsplus_cat_read_inode(struct inode *inode, struct hfs_find_data *fd)
 		}
 		hfs_bnode_read(fd->bnode, &entry, fd->entryoffset,
 					sizeof(struct hfsplus_cat_folder));
-		hfsplus_get_perms(inode, &folder->permissions, 1);
+		res = hfsplus_get_perms(inode, &folder->permissions, 1);
+		if (res)
+			goto out;
 		set_nlink(inode, 1);
 		inode->i_size = 2 + be32_to_cpu(folder->valence);
 		inode_set_atime_to_ts(inode, hfsp_mt2ut(folder->access_date));
@@ -545,7 +567,9 @@ int hfsplus_cat_read_inode(struct inode *inode, struct hfs_find_data *fd)
 
 		hfsplus_inode_read_fork(inode, HFSPLUS_IS_RSRC(inode) ?
 					&file->rsrc_fork : &file->data_fork);
-		hfsplus_get_perms(inode, &file->permissions, 0);
+		res = hfsplus_get_perms(inode, &file->permissions, 0);
+		if (res)
+			goto out;
 		set_nlink(inode, 1);
 		if (S_ISREG(inode->i_mode)) {
 			if (file->permissions.dev)