linux-kernel - [PATCH -next v5 5/8] xfs: correct the truncate blocksize of realtime inode

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Message-Id: <20240613090033.2246907-6-yi.zhang@huaweicloud.com>
Date: Thu, 13 Jun 2024 17:00:30 +0800
From: Zhang Yi <yi.zhang@...weicloud.com>
To: linux-xfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	djwong@...nel.org,
	hch@...radead.org,
	brauner@...nel.org,
	david@...morbit.com,
	chandanbabu@...nel.org,
	jack@...e.cz,
	yi.zhang@...wei.com,
	yi.zhang@...weicloud.com,
	chengzhihao1@...wei.com,
	yukuai3@...wei.com
Subject: [PATCH -next v5 5/8] xfs: correct the truncate blocksize of realtime inode

From: Zhang Yi <yi.zhang@...wei.com>

When unaligned truncating down a realtime file which sb_rextsize is
bigger than one block, xfs_truncate_page() only zeros out the tail EOF
block, this could expose stale data since commit '943bc0882ceb ("iomap:
don't increase i_size if it's not a write operation")'.

If we truncate file that contains a large enough written extent:

     |<    rxext    >|<    rtext    >|
  ...WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW
        ^ (new EOF)      ^ old EOF

Since we only zeros out the tail of the EOF block, and
xfs_itruncate_extents() unmap the whole ailgned extents, it becomes
this state:

     |<    rxext    >|
  ...WWWzWWWWWWWWWWWWW
        ^ new EOF

Then if we do an extending write like this, the blocks in the previous
tail extent becomes stale:

     |<    rxext    >|
  ...WWWzSSSSSSSSSSSSS..........WWWWWWWWWWWWWWWWW
        ^ old EOF               ^ append start  ^ new EOF

Fix this by zeroing out the tail allocation uint and also make sure
xfs_itruncate_extents() unmap allocation uint aligned extents.

Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
---
 fs/xfs/xfs_inode.c | 3 ++-
 fs/xfs/xfs_iops.c  | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 58fb7a5062e1..92daa2279053 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -1511,7 +1511,8 @@ xfs_itruncate_extents_flags(
 	 * We have to free all the blocks to the bmbt maximum offset, even if
 	 * the page cache can't scale that far.
 	 */
-	first_unmap_block = XFS_B_TO_FSB(mp, (xfs_ufsize_t)new_size);
+	first_unmap_block = XFS_B_TO_FSB(mp,
+			roundup_64(new_size, xfs_inode_alloc_unitsize(ip)));
 	if (!xfs_verify_fileoff(mp, first_unmap_block)) {
 		WARN_ON_ONCE(first_unmap_block > XFS_MAX_FILEOFF);
 		return 0;
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 0919a42cceb6..8e7e6c435fb3 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -858,7 +858,7 @@ xfs_setattr_truncate_data(
 	}
 
 	/* Truncate down */
-	blocksize = i_blocksize(inode);
+	blocksize = xfs_inode_alloc_unitsize(ip);
 
 	/*
 	 * iomap won't detect a dirty page over an unwritten block (or a cow
-- 
2.39.2