linux-ext4 - [PATCH v2] ext4: Fix i_disksize exceeding i_size problem in paritally written case

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Date:   Tue, 21 Mar 2023 09:37:21 +0800
From:   Zhihao Cheng <chengzhihao1@...wei.com>
To:     <tytso@....edu>, <adilger.kernel@...ger.ca>, <jack@...e.com>,
        <tudor.ambarus@...aro.org>
CC:     <linux-ext4@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <chengzhihao1@...wei.com>, <yi.zhang@...wei.com>
Subject: [PATCH v2] ext4: Fix i_disksize exceeding i_size problem in paritally written case

Following process makes i_disksize exceed i_size:

generic_perform_write
 copied = iov_iter_copy_from_user_atomic(len) // copied < len
 ext4_da_write_end
 | ext4_update_i_disksize
 |  new_i_size = pos + copied;
 |  WRITE_ONCE(EXT4_I(inode)->i_disksize, newsize) // update i_disksize
 | generic_write_end
 |  copied = block_write_end(copied, len) // copied = 0
 |   if (unlikely(copied < len))
 |    if (!PageUptodate(page))
 |     copied = 0;
 |  if (pos + copied > inode->i_size) // return false
 if (unlikely(copied == 0))
  goto again;
 if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
  status = -EFAULT;
  break;
 }

We get i_disksize greater than i_size here, which could trigger WARNING
check 'i_size_read(inode) < EXT4_I(inode)->i_disksize' while doing dio:

ext4_dio_write_iter
 iomap_dio_rw
  __iomap_dio_rw // return err, length is not aligned to 512
 ext4_handle_inode_extension
  WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize) // Oops

 WARNING: CPU: 2 PID: 2609 at fs/ext4/file.c:319
 CPU: 2 PID: 2609 Comm: aa Not tainted 6.3.0-rc2
 RIP: 0010:ext4_file_write_iter+0xbc7
 Call Trace:
  vfs_write+0x3b1
  ksys_write+0x77
  do_syscall_64+0x39

Fix it by updating 'copied' value before updating i_disksize just like
ext4_write_inline_data_end() does.

Fetch a reproducer in [Link].

Link: https://bugzilla.kernel.org/show_bug.cgi?id=217209
Fixes: 64769240bd07 ("ext4: Add delayed allocation support in data=writeback mode")
Signed-off-by: Zhihao Cheng <chengzhihao1@...wei.com>
---
 v1->v2: Check and update 'copied' value before updating i_disksize rather
	 than opencoding generic_write_end().
 fs/ext4/inode.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index bf0b7dea4900..41ba1c432844 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3148,6 +3148,9 @@ static int ext4_da_write_end(struct file *file,
 	    ext4_has_inline_data(inode))
 		return ext4_write_inline_data_end(inode, pos, len, copied, page);
 
+	if (unlikely(copied < len) && !PageUptodate(page))
+		copied = 0;
+
 	start = pos & (PAGE_SIZE - 1);
 	end = start + copied - 1;
 
-- 
2.31.1