cifs: mtime lost when copying to a share

[antoileb]

Describe the bug

When copying files to a cifs share with -p, the mtime attributes are lost. I'm fairly confident other attributes are also lost but I've only looked out for mtime.
This issue occurs since kernel version 6.12.62+rpt-rpi-v8 (on Raspberry Pi OS Trixie) and downgrading to 6.12.47+rpt-rpi-v8 fixes the issue.

Steps to reproduce the behaviour

• mount a CIFS share mount -t cifs //<host>/home /mnt/nas
• copy files using cp -p to this network share cp -p /home/hiver/test/file.pdf /mnt/nas/

hiver@rpi:~/test $ stat -c "%y" file.pdf
2026-01-25 15:11:40.580874684 +0100
hiver@rpi:~/test $ cp -p file.pdf /mnt/nas
hiver@rpi:~/test $ stat -c "%y" /mnt/nas/file.pdf
2026-01-25 15:12:46.343470200 +0100 # the mtime has changed

The same under 6.12.47:

hiver@rpi:~ $ stat -c "%y" /mnt/nas/file.pdf
2026-01-25 15:11:40.580874600 +0100 # the same as the source file

Device (s)

Raspberry Pi 3 Mod. B+

System

# cat /etc/rpi-issue
Raspberry Pi reference 2024-03-15
Generated using pi-gen, https://github.com/RPi-Distro/pi-gen, f19ee211ddafcae3008
27f953d143de92a5c6624, stage2

# vcgencmd version
Aug 20 2025 17:04:09
Copyright (c) 2012 Broadcom
version cd866525580337c0aee4b25880e1f5f9f674fb24 (clean) (release) (start)

# uname -a
Linux rpi 6.12.62+rpt-rpi-v8 #1 SMP PREEMPT Debian 1:6.12.62-1+rpt1 (2025-12-18) aarch64 GNU/Linux

Logs

I wasn't able to find anything releveant in the logs

Additional context

I initially encountered this issue while using FreeFileSync using SFTP and other users of the same software also encountered this issue on different hardware/software. I'm quite sure this is a upstream kernel bug introduced during 6.18 and then backported to 6.12, but as I am unable to check against a upstream kernel build, I'm reporting this issue here

[pelwell]

I can't see any changes to the CIFS code on rpi-6.12.y since Linux 6.12.36, which makes your assertion that 6.12.47 was OK but 6.12.62 is bad confusing.