ext4: detect invalid INLINE_DATA + EXTENTS flag combination

commit 1d3ad18 upstream.

syzbot reported a BUG_ON in ext4_es_cache_extent() when opening a verity
file on a corrupted ext4 filesystem mounted without a journal.

The issue is that the filesystem has an inode with both the INLINE_DATA
and EXTENTS flags set:

    EXT4-fs error (device loop0): ext4_cache_extents:545: inode #15:
    comm syz.0.17: corrupted extent tree: lblk 0 < prev 66

Investigation revealed that the inode has both flags set:
    DEBUG: inode 15 - flag=1, i_inline_off=164, has_inline=1, extents_flag=1

This is an invalid combination since an inode should have either:
- INLINE_DATA: data stored directly in the inode
- EXTENTS: data stored in extent-mapped blocks

Having both flags causes ext4_has_inline_data() to return true, skipping
extent tree validation in __ext4_iget(). The unvalidated out-of-order
extents then trigger a BUG_ON in ext4_es_cache_extent() due to integer
underflow when calculating hole sizes.

Fix this by detecting this invalid flag combination early in ext4_iget()
and rejecting the corrupted inode.

Cc: stable@kernel.org
Reported-and-tested-by: syzbot+038b7bf43423e132b308@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=038b7bf43423e132b308
Suggested-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Message-ID: <20250930112810.315095-1-kartikey406@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: deepanshu406

fs/ext4/inode.c

@@ -4868,6 +4868,14 @@ struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
 	}
 	ei->i_flags = le32_to_cpu(raw_inode->i_flags);
 	ext4_set_inode_flags(inode, true);
+	/* Detect invalid flag combination - can't have both inline data and extents */
+	if (ext4_test_inode_flag(inode, EXT4_INODE_INLINE_DATA) &&
+	    ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
+		ext4_error_inode(inode, function, line, 0,
+			"inode has both inline data and extents flags");
+		ret = -EFSCORRUPTED;
+		goto bad_inode;
+	}
 	inode->i_blocks = ext4_inode_blocks(raw_inode, ei);
 	ei->i_file_acl = le32_to_cpu(raw_inode->i_file_acl_lo);
 	if (ext4_has_feature_64bit(sb))