linux-kernel - [PATCH 3.19.y-ckt 020/107] ext4: correctly migrate a file with a hole at the beginning

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Message-Id: <1438811379-384-21-git-send-email-kamal@canonical.com>
Date:	Wed,  5 Aug 2015 14:48:12 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Eryu Guan <guaneryu@...il.com>, Theodore Ts'o <tytso@....edu>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 020/107] ext4: correctly migrate a file with a hole at the beginning

3.19.8-ckt5 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eryu Guan <guaneryu@...il.com>

commit 8974fec7d72e3e02752fe0f27b4c3719c78d9a15 upstream.

Currently ext4_ind_migrate() doesn't correctly handle a file which
contains a hole at the beginning of the file.  This caused the migration
to be done incorrectly, and then if there is a subsequent following
delayed allocation write to the "hole", this would reclaim the same data
blocks again and results in fs corruption.

  # assmuing 4k block size ext4, with delalloc enabled
  # skip the first block and write to the second block
  xfs_io -fc "pwrite 4k 4k" -c "fsync" /mnt/ext4/testfile

  # converting to indirect-mapped file, which would move the data blocks
  # to the beginning of the file, but extent status cache still marks
  # that region as a hole
  chattr -e /mnt/ext4/testfile

  # delayed allocation writes to the "hole", reclaim the same data block
  # again, results in i_blocks corruption
  xfs_io -c "pwrite 0 4k" /mnt/ext4/testfile
  umount /mnt/ext4
  e2fsck -nf /dev/sda6
  ...
  Inode 53, i_blocks is 16, should be 8.  Fix? no
  ...

Signed-off-by: Eryu Guan <guaneryu@...il.com>
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 fs/ext4/migrate.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/migrate.c b/fs/ext4/migrate.c
index 0b868f0..bad30c6 100644
--- a/fs/ext4/migrate.c
+++ b/fs/ext4/migrate.c
@@ -620,7 +620,7 @@ int ext4_ind_migrate(struct inode *inode)
 	struct ext4_inode_info		*ei = EXT4_I(inode);
 	struct ext4_extent		*ex;
 	unsigned int			i, len;
-	ext4_lblk_t			end;
+	ext4_lblk_t			start, end;
 	ext4_fsblk_t			blk;
 	handle_t			*handle;
 	int				ret;
@@ -659,11 +659,12 @@ int ext4_ind_migrate(struct inode *inode)
 		goto errout;
 	}
 	if (eh->eh_entries == 0)
-		blk = len = 0;
+		blk = len = start = end = 0;
 	else {
 		len = le16_to_cpu(ex->ee_len);
 		blk = ext4_ext_pblock(ex);
-		end = le32_to_cpu(ex->ee_block) + len - 1;
+		start = le32_to_cpu(ex->ee_block);
+		end = start + len - 1;
 		if (end >= EXT4_NDIR_BLOCKS) {
 			ret = -EOPNOTSUPP;
 			goto errout;
@@ -672,7 +673,7 @@ int ext4_ind_migrate(struct inode *inode)
 
 	ext4_clear_inode_flag(inode, EXT4_INODE_EXTENTS);
 	memset(ei->i_data, 0, sizeof(ei->i_data));
-	for (i=0; i < len; i++)
+	for (i = start; i <= end; i++)
 		ei->i_data[i] = cpu_to_le32(blk++);
 	ext4_mark_inode_dirty(handle, inode);
 errout:
-- 
1.9.1

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