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

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

[Frank Hsiao 蕭法宣]

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. 

Signed-off-by: Frank Hsiao 蕭法宣 <frankhsiao@qnap.com>

diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c
index b2f6a1937d239..19dbe9d1187e1 100644
--- a/fs/ecryptfs/main.c
+++ b/fs/ecryptfs/main.c
@@ -567,6 +567,7 @@ static struct dentry *ecryptfs_mount(struct file_system_type
 *fs_type, int flags
 	s->s_blocksize = path.dentry->d_sb->s_blocksize;
 	s->s_magic = ECRYPTFS_SUPER_MAGIC;
 	s->s_stack_depth = path.dentry->d_sb->s_stack_depth + 1;
+	s->s_time_gran = path.dentry->d_sb->s_time_gran;
 
 	rc = -EINVAL;
 	if (s->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {

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

[Bert Wesarg]

Hi,

On 17.05.24 12:09, 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

was there some discussion for this solution. I came to the same conclusion but cannot test it right now.

Thanks
Bert

> 
> 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.
> 
> Signed-off-by: Frank Hsiao 蕭法宣 <frankhsiao@qnap.com>
> 
> diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c
> index b2f6a1937d239..19dbe9d1187e1 100644
> --- a/fs/ecryptfs/main.c
> +++ b/fs/ecryptfs/main.c
> @@ -567,6 +567,7 @@ static struct dentry *ecryptfs_mount(struct file_system_type
>   *fs_type, int flags
>   	s->s_blocksize = path.dentry->d_sb->s_blocksize;
>   	s->s_magic = ECRYPTFS_SUPER_MAGIC;
>   	s->s_stack_depth = path.dentry->d_sb->s_stack_depth + 1;
> +	s->s_time_gran = path.dentry->d_sb->s_time_gran;
>   
>   	rc = -EINVAL;
>   	if (s->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {

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

[Frank Hsiao 蕭法宣]

Friendly ping, thanks.

________________________________________
寄件者: Frank Hsiao 蕭法宣 <frankhsiao@qnap.com>
寄件日期: 2024年5月17日 下午 06:09
收件者: code@tyhicks.com
副本: ecryptfs@vger.kernel.org
主旨: [PATCH] ecryptfs: set s_time_gran to get correct time granularity

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.

Signed-off-by: Frank Hsiao 蕭法宣 <frankhsiao@qnap.com>

diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c
index b2f6a1937d239..19dbe9d1187e1 100644
--- a/fs/ecryptfs/main.c
+++ b/fs/ecryptfs/main.c
@@ -567,6 +567,7 @@ static struct dentry *ecryptfs_mount(struct file_system_type
 *fs_type, int flags
        s->s_blocksize = path.dentry->d_sb->s_blocksize;
        s->s_magic = ECRYPTFS_SUPER_MAGIC;
        s->s_stack_depth = path.dentry->d_sb->s_stack_depth + 1;
+       s->s_time_gran = path.dentry->d_sb->s_time_gran;

        rc = -EINVAL;
        if (s->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {

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

[Bert Wesarg]

Dear all,

On Fri, Dec 6, 2024 at 1:29 PM Bert Wesarg <bert.wesarg@googlemail.com> wrote:
>
> Hi,
>
> On 17.05.24 12:09, 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
>
> was there some discussion for this solution. I came to the same conclusion but cannot test it right now.

now that there is renewed activity in eCryptfs (thanks, btw). Can we
please consider this patch for a next cycle?

Thanks.

Best
Bert

>
> Thanks
> Bert
>
> >
> > 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.
> >
> > Signed-off-by: Frank Hsiao 蕭法宣 <frankhsiao@qnap.com>
> >
> > diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c
> > index b2f6a1937d239..19dbe9d1187e1 100644
> > --- a/fs/ecryptfs/main.c
> > +++ b/fs/ecryptfs/main.c
> > @@ -567,6 +567,7 @@ static struct dentry *ecryptfs_mount(struct file_system_type
> >   *fs_type, int flags
> >       s->s_blocksize = path.dentry->d_sb->s_blocksize;
> >       s->s_magic = ECRYPTFS_SUPER_MAGIC;
> >       s->s_stack_depth = path.dentry->d_sb->s_stack_depth + 1;
> > +     s->s_time_gran = path.dentry->d_sb->s_time_gran;
> >
> >       rc = -EINVAL;
> >       if (s->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {

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

[Tyler Hicks]

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