punch_hole are the places 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. Even more i_mutex is not holded while punch_hole
which obviously result in dangerous data corruption due to
access-after-free issue.
This patch performs following changes:
- Guard punch_hole with 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 there is
no easy way to stop writeback while punch_hole is in progress.
Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
---
fs/ext4/extents.c | 41 +++++++++++++++++++++++++----------------
1 files changed, 25 insertions(+), 16 deletions(-)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 44e33b0..0e94485 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4814,9 +4814,22 @@ 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);
/* 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
@@ -4834,31 +4847,23 @@ 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);
ext4_flush_completed_IO(inode);
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;
+ }
err = ext4_orphan_add(handle, inode);
if (err)
@@ -4952,6 +4957,10 @@ 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,
--
1.7.7.6
--
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