fsync and 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 write-after-free.
This patch performs following changes:
- Guard punch_hole with i_mutex
- fsync and punch_hole now wait for all writers in flight
NOTE: XXX write-after-free race is still possible because
truncate_pagecache_range() is not completely reliable and where
is no easy way to stop writeback while punch_hole is in progress.
Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
---
fs/ext4/extents.c | 10 ++++++++--
fs/ext4/fsync.c | 1 +
2 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index e993879..8252651 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4845,6 +4845,7 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length)
return err;
}
+ mutex_lock(&inode->i_mutex);
/* Now release the pages */
if (last_page_offset > first_page_offset) {
truncate_pagecache_range(inode, first_page_offset,
@@ -4852,12 +4853,15 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length)
}
/* finish any pending end_io work */
+ 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_mutex;
+ }
err = ext4_orphan_add(handle, inode);
if (err)
@@ -4951,6 +4955,8 @@ out:
inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
ext4_mark_inode_dirty(handle, inode);
ext4_journal_stop(handle);
+out_mutex:
+ mutex_unlock(&inode->i_mutex);
return err;
}
int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
index 24f3719..290c5cf 100644
--- a/fs/ext4/fsync.c
+++ b/fs/ext4/fsync.c
@@ -204,6 +204,7 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
if (inode->i_sb->s_flags & MS_RDONLY)
goto out;
+ inode_dio_wait(inode);
ret = ext4_flush_completed_IO(inode);
if (ret < 0)
goto out;
--
1.7.7.6
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