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ext4: punch_hole should wait for DIO writers

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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: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Dmitry Monakhov 2012-09-30 23:03:42 -04:00 committed by Theodore Ts'o
parent 1f555cfa29
commit 02d262dffc
1 changed files with 36 additions and 17 deletions
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53
fs/ext4/extents.c
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@ -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 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length)
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,