Code:  static void ext4_invalidatepage(struct page *page, unsigned long offset)
 {
 	journal_t *journal = EXT4_JOURNAL(page->mapping->host);
 
 	/*
 	 * If it's a full truncate we just forget about the pending dirtying
 	 */
	if (offset == 0)
		ClearPageChecked(page);

	if (journal)
		jbd2_journal_invalidatepage(journal, page, offset);
	else
		block_invalidatepage(page, offset);
}

Vulnerability Type: DoS 
CWE ID: 
Summary: The ext4 implementation in the Linux kernel before 2.6.34 does not properly track the initialization of certain data structures, which allows physically proximate attackers to cause a denial of service (NULL pointer dereference and panic) via a crafted USB device, related to the ext4_fill_super function.
Commit Message: ext4: use ext4_get_block_write in buffer write

Allocate uninitialized extent before ext4 buffer write and
convert the extent to initialized after io completes.
The purpose is to make sure an extent can only be marked
initialized after it has been written with new data so
we can safely drop the i_mutex lock in ext4 DIO read without
exposing stale data. This helps to improve multi-thread DIO
read performance on high-speed disks.

Skip the nobh and data=journal mount cases to make things simple for now.

Signed-off-by: Jiaying Zhang <jiayingz@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>