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Commit 02d262df authored by Dmitry Monakhov's avatar Dmitry Monakhov Committed by Theodore Ts'o
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ext4: punch_hole should wait for DIO writers 



punch_hole is the place where we have to wait for all existing writers
(writeback, aio, dio), but currently we simply flush pended end_io request
which is not sufficient. Other issue is that punch_hole performed w/o i_mutex
held which obviously result in dangerous data corruption due to
write-after-free.

This patch performs following changes:
- Guard punch_hole with i_mutex
- Recheck inode flags under i_mutex
- Block all new dio readers in order to prevent information leak caused by
  read-after-free pattern.
- punch_hole now wait for all writers in flight
  NOTE: XXX write-after-free race is still possible because new dirty pages
  may appear due to mmap(), and currently there is no easy way to stop
  writeback while punch_hole is in progress.

[ Fixed error return from ext4_ext_punch_hole() to make sure that we
  release i_mutex before returning EPERM or ETXTBUSY -- Ted ]

Signed-off-by: default avatarDmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 1f555cfa

fs/ext4/extents.c

+36 −17
Original line number Diff line number Diff line
@@ -4794,9 +4794,32 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length) 
	loff_t first_page_offset, last_page_offset;

	int credits, err = 0;



	/*

	 * Write out all dirty pages to avoid race conditions

	 * Then release them.

	 */

	if (mapping->nrpages && mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {

		err = filemap_write_and_wait_range(mapping,

			offset, offset + length - 1);



		if (err)

			return err;

	}



	mutex_lock(&inode->i_mutex);

	/* It's not possible punch hole on append only file */

	if (IS_APPEND(inode) || IS_IMMUTABLE(inode)) {

		err = -EPERM;

		goto out_mutex;

	}

	if (IS_SWAPFILE(inode)) {

		err = -ETXTBSY;

		goto out_mutex;

	}



	/* No need to punch hole beyond i_size */

	if (offset >= inode->i_size)

		return 0;

		goto out_mutex;



	/*

	 * If the hole extends beyond i_size, set the hole
@@ -4814,33 +4837,25 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length) 
	first_page_offset = first_page << PAGE_CACHE_SHIFT;

	last_page_offset = last_page << PAGE_CACHE_SHIFT;



	/*

	 * Write out all dirty pages to avoid race conditions

	 * Then release them.

	 */

	if (mapping->nrpages && mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {

		err = filemap_write_and_wait_range(mapping,

			offset, offset + length - 1);



		if (err)

			return err;

	}



	/* Now release the pages */

	if (last_page_offset > first_page_offset) {

		truncate_pagecache_range(inode, first_page_offset,

					 last_page_offset - 1);

	}



	/* finish any pending end_io work */

	/* Wait all existing dio workers, newcomers will block on i_mutex */

	ext4_inode_block_unlocked_dio(inode);

	inode_dio_wait(inode);

	err = ext4_flush_completed_IO(inode);

	if (err)

		return err;

		goto out_dio;



	credits = ext4_writepage_trans_blocks(inode);

	handle = ext4_journal_start(inode, credits);

	if (IS_ERR(handle))

		return PTR_ERR(handle);

	if (IS_ERR(handle)) {

		err = PTR_ERR(handle);

		goto out_dio;

	}





	/*
@@ -4930,6 +4945,10 @@ out: 
	inode->i_mtime = inode->i_ctime = ext4_current_time(inode);

	ext4_mark_inode_dirty(handle, inode);

	ext4_journal_stop(handle);

out_dio:

	ext4_inode_resume_unlocked_dio(inode);

out_mutex:

	mutex_unlock(&inode->i_mutex);

	return err;

}

int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,