ext4: add EXT4_IGET_BAD flag to prevent unexpected bad inode

There are many places that will get unhappy (and crash) when ext4_iget()
returns a bad inode. However, if iget the boot loader inode, allows a bad
inode to be returned, because the inode may not be initialized. This
mechanism can be used to bypass some checks and cause panic. To solve this
problem, we add a special iget flag EXT4_IGET_BAD. Only with this flag
we'd be returning bad inode from ext4_iget(), otherwise we always return
the error code if the inode is bad inode.(suggested by Jan Kara)

Signed-off-by: Baokun Li <[email protected]>
Reviewed-by: Jason Yan <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>
Cc: [email protected]

Author: LiBaokun96

fs/ext4/ext4.h

@@ -2964,7 +2964,8 @@ int do_journal_get_write_access(handle_t *handle, struct inode *inode,
 typedef enum {
 	EXT4_IGET_NORMAL =	0,
 	EXT4_IGET_SPECIAL =	0x0001, /* OK to iget a system inode */
-	EXT4_IGET_HANDLE = 	0x0002	/* Inode # is from a handle */
+	EXT4_IGET_HANDLE = 	0x0002,	/* Inode # is from a handle */
+	EXT4_IGET_BAD =		0x0004  /* Allow to iget a bad inode */
 } ext4_iget_flags;
 
 extern struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,

fs/ext4/inode.c

@@ -5058,8 +5058,14 @@ struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
 	if (IS_CASEFOLDED(inode) && !ext4_has_feature_casefold(inode->i_sb))
 		ext4_error_inode(inode, function, line, 0,
 				 "casefold flag without casefold feature");
-	brelse(iloc.bh);
+	if (is_bad_inode(inode) && !(flags & EXT4_IGET_BAD)) {
+		ext4_error_inode(inode, function, line, 0,
+				 "bad inode without EXT4_IGET_BAD flag");
+		ret = -EUCLEAN;
+		goto bad_inode;
+	}
 
+	brelse(iloc.bh);
 	unlock_new_inode(inode);
 	return inode;
 

fs/ext4/ioctl.c

@@ -374,7 +374,8 @@ static long swap_inode_boot_loader(struct super_block *sb,
 	blkcnt_t blocks;
 	unsigned short bytes;
 
-	inode_bl = ext4_iget(sb, EXT4_BOOT_LOADER_INO, EXT4_IGET_SPECIAL);
+	inode_bl = ext4_iget(sb, EXT4_BOOT_LOADER_INO,
+			EXT4_IGET_SPECIAL | EXT4_IGET_BAD);
 	if (IS_ERR(inode_bl))
 		return PTR_ERR(inode_bl);
 	ei_bl = EXT4_I(inode_bl);