Re: [PATCH] ecryptfs: set s_time_gran to get correct time granularity

[Tyler Hicks <code@tyhicks.com>]

On 2024-05-17 10:09:55, Frank Hsiao 蕭法宣 wrote:
> related to: https://bugs.launchpad.net/ecryptfs/+bug/1890486
> 
> This bug happens in the two following situations:
> cp -p: copy a file and preserve its atime and mtime
> touch -r: touch a file and use a ref file's time instead of current time
> 
> In fs/attr.c notify_change(), atime and mtime is truncated by timestamp_truncate(),
> ecryptfs gets wrong s_time_gran (10^9 instead of original fs time granularity) and
> truncates a/mtime to whole second. Setting s_time_gran when mounting ecryptfs
>  solves the issue. 

Thank you! This has been applied to the next branch of the
tyhicks/ecryptfs.git tree.

I apologize that this fix was forgotten for so long. Thanks to Bert for
raising it back up to my attention.

Given the long delay since you've sent this patch, I went ahead and
slightly modified the commit message to make it follow the guidelines
documented in the Documentation/process/submitting-patches.rst file. Let
me know if you have any objections:

===
ecryptfs: Set s_time_gran to get correct time granularity

Set the eCryptfs superblock time granularity, using the lower
filesystem's s_time_gran value, to prevent unnecessary inode timestamp
truncation to the granularity of a full second.

The use of utimensat(2) to set a timestamp with nanosecond precision
would trigger this bug. That occurred when using the following utilities
to update timestamps of a file:
  * cp -p: copy a file and preserve its atime and mtime
  * touch -r: touch a file and use a reference file's timestamps

Closes: https://bugs.launchpad.net/ecryptfs/+bug/1890486
Signed-off-by: Frank Hsiao 蕭法宣 <frankhsiao@qnap.com>
[tyhicks: Partially rewrite the commit message]
Signed-off-by: Tyler Hicks <code@tyhicks.com>
===

You can find a direct link below but please be aware that the commit hash is
unstable and, therefore, the URL may not be valid in the future.

[1/1] ecryptfs: Set s_time_gran to get correct time granularity
      https://git.kernel.org/tyhicks/ecryptfs/c/7d9ebf33d85317f3f258c627de51701e2bf7642d

Tyler