[PATCH 6/6] xfs: port xfs_ioc_start_commit to multigrain timestamps

Darrick J. Wong
2024-12-04T03:03:48Z

From: Darrick J. Wong <djwong@kernel.org>

Take advantage of the multigrain timestamp APIs to ensure that nobody
can sneak in and write things to a file between starting a file update
operation and committing the results. This should have been part of the
multigrain timestamp merge, but I forgot to fling it at jlayton when he
resubmitted the patchset due to developer bandwidth problems.

Cc: jlayton@kernel.org
Cc: <stable@vger.kernel.org> # v6.13-rc1
Fixes: 4e40eff0b5737c ("fs: add infrastructure for multigrain timestamps")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
fs/xfs/xfs_exchrange.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/fs/xfs/xfs_exchrange.c b/fs/xfs/xfs_exchrange.c
index 9ab05ad224d127..dd24de420714ab 100644
--- a/fs/xfs/xfs_exchrange.c
+++ b/fs/xfs/xfs_exchrange.c
@@ -854,7 +854,7 @@ xfs_ioc_start_commit(
struct xfs_commit_range __user *argp)
{
struct xfs_commit_range args = { };
- struct timespec64 ts;
+ struct kstat kstat;
struct xfs_commit_range_fresh *kern_f;
struct xfs_commit_range_fresh __user *user_f;
struct inode *inode2 = file_inode(file);
@@ -871,12 +871,12 @@ xfs_ioc_start_commit(
memcpy(&kern_f->fsid, ip2->i_mount->m_fixedfsid, sizeof(xfs_fsid_t));

xfs_ilock(ip2, lockflags);
- ts = inode_get_ctime(inode2);
- kern_f->file2_ctime = ts.tv_sec;
- kern_f->file2_ctime_nsec = ts.tv_nsec;
- ts = inode_get_mtime(inode2);
- kern_f->file2_mtime = ts.tv_sec;
- kern_f->file2_mtime_nsec = ts.tv_nsec;
+ /* Force writing of a distinct ctime if any writes happen. */
+ fill_mg_cmtime(&kstat, STATX_CTIME | STATX_MTIME, inode2);
+ kern_f->file2_ctime = kstat.ctime.tv_sec;
+ kern_f->file2_ctime_nsec = kstat.ctime.tv_nsec;
+ kern_f->file2_mtime = kstat.mtime.tv_sec;
+ kern_f->file2_mtime_nsec = kstat.mtime.tv_nsec;
kern_f->file2_ino = ip2->i_ino;
kern_f->file2_gen = inode2->i_generation;
kern_f->magic = XCR_FRESH_MAGIC;