FAILED: patch "[PATCH] exfat: advance valid_size to EOF for append writes" failed to apply to 6.12-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x b70ab407503706289163dd59f1ac3e942bacc37d
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107052509-failed-6.12-b70ab4075037@kernel.org' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From b70ab407503706289163dd59f1ac3e942bacc37d Mon Sep 17 00:00:00 2001
From: Chi Zhiling <chizhiling@kylinos.cn>
Date: Sun, 4 Oct 2026 18:19:30 +0800
Subject: [PATCH] exfat: advance valid_size to EOF for append writes

For an append write, the write position is recalculated by
generic_write_checks(). Therefore, the write position must be obtained
after generic_write_checks() returns.

Using the original write position to advance valid_size may cause the
valid_size update to be skipped, potentially exposing stale data.

Also move the truncate_pagecache() check below the recalculated
position, so that pos is never read before it is assigned.

Fixes: 11a347fb6cef ("exfat: change to get file size from DataLength")
Cc: stable@vger.kernel.org
Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
---
 fs/exfat/file.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/fs/exfat/file.c b/fs/exfat/file.c
index 3867e78c23125..87afb6bffd353 100644
--- a/fs/exfat/file.c
+++ b/fs/exfat/file.c
@@ -854,8 +854,7 @@ static ssize_t exfat_file_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 	struct file *file = iocb->ki_filp;
 	struct inode *inode = file_inode(file);
 	struct exfat_inode_info *ei = EXFAT_I(inode);
-	loff_t pos = iocb->ki_pos;
-	loff_t valid_size;
+	loff_t pos, valid_size;
 	int err;
 
 	if (unlikely(exfat_forced_shutdown(inode->i_sb)))
@@ -863,11 +862,6 @@ static ssize_t exfat_file_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 
 	inode_lock(inode);
 
-	if (pos > i_size_read(inode))
-		truncate_pagecache(inode, i_size_read(inode));
-
-	valid_size = ei->valid_size;
-
 	ret = generic_write_checks(iocb, iter);
 	if (ret <= 0)
 		goto unlock;
@@ -878,6 +872,11 @@ static ssize_t exfat_file_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 		goto unlock;
 	}
 
+	pos = iocb->ki_pos;
+	if (pos > i_size_read(inode))
+		truncate_pagecache(inode, i_size_read(inode));
+
+	valid_size = ei->valid_size;
 	if (pos > valid_size) {
 		ret = exfat_extend_valid_size(inode, pos);
 		if (ret < 0 && ret != -ENOSPC) {
@@ -887,6 +886,8 @@ static ssize_t exfat_file_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 		}
 		if (ret < 0)
 			goto unlock;
+
+		pos = valid_size;
 	}
 
 	if (iocb->ki_flags & IOCB_DIRECT)
@@ -899,9 +900,6 @@ static ssize_t exfat_file_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 
 	inode_unlock(inode);
 
-	if (pos > valid_size)
-		pos = valid_size;
-
 	if (iocb->ki_pos > pos) {
 		ssize_t err = generic_write_sync(iocb, iocb->ki_pos - pos);
 
-- 
2.53.0