linux-kernel - Re: [PATCH 05/20] utimes: Clamp the timestamps before update

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Date:   Wed, 31 Jul 2019 08:14:52 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Deepa Dinamani <deepa.kernel@...il.com>
Cc:     viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, arnd@...db.de,
        y2038@...ts.linaro.org
Subject: Re: [PATCH 05/20] utimes: Clamp the timestamps before update

On Mon, Jul 29, 2019 at 06:49:09PM -0700, Deepa Dinamani wrote:
> POSIX is ambiguous on the behavior of timestamps for
> futimens, utimensat and utimes. Whether to return an
> error or silently clamp a timestamp beyond the range
> supported by the underlying filesystems is not clear.
> 
> POSIX.1 section for futimens, utimensat and utimes says:
> (http://pubs.opengroup.org/onlinepubs/9699919799/functions/futimens.html)
> 
> The file's relevant timestamp shall be set to the greatest
> value supported by the file system that is not greater
> than the specified time.
> 
> If the tv_nsec field of a timespec structure has the special
> value UTIME_NOW, the file's relevant timestamp shall be set
> to the greatest value supported by the file system that is
> not greater than the current time.
> 
> [EINVAL]
>     A new file timestamp would be a value whose tv_sec
>     component is not a value supported by the file system.
> 
> The patch chooses to clamp the timestamps according to the
> filesystem timestamp ranges and does not return an error.
> This is in line with the behavior of utime syscall also
> since the POSIX page(http://pubs.opengroup.org/onlinepubs/009695399/functions/utime.html)
> for utime does not mention returning an error or clamping like above.
> 
> Same for utimes http://pubs.opengroup.org/onlinepubs/009695399/functions/utimes.html
> 
> Signed-off-by: Deepa Dinamani <deepa.kernel@...il.com>
> ---
>  fs/utimes.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/utimes.c b/fs/utimes.c
> index 350c9c16ace1..4c1a2ce90bbc 100644
> --- a/fs/utimes.c
> +++ b/fs/utimes.c
> @@ -21,6 +21,7 @@ static int utimes_common(const struct path *path, struct timespec64 *times)
>  	int error;
>  	struct iattr newattrs;
>  	struct inode *inode = path->dentry->d_inode;
> +	struct super_block *sb = inode->i_sb;
>  	struct inode *delegated_inode = NULL;
>  
>  	error = mnt_want_write(path->mnt);
> @@ -36,16 +37,24 @@ static int utimes_common(const struct path *path, struct timespec64 *times)
>  		if (times[0].tv_nsec == UTIME_OMIT)
>  			newattrs.ia_valid &= ~ATTR_ATIME;
>  		else if (times[0].tv_nsec != UTIME_NOW) {
> -			newattrs.ia_atime.tv_sec = times[0].tv_sec;
> -			newattrs.ia_atime.tv_nsec = times[0].tv_nsec;
> +			newattrs.ia_atime.tv_sec =
> +				clamp(times[0].tv_sec, sb->s_time_min, sb->s_time_max);
> +			if (times[0].tv_sec == sb->s_time_max || times[0].tv_sec == sb->s_time_min)
> +				newattrs.ia_atime.tv_nsec = 0;
> +			else
> +				newattrs.ia_atime.tv_nsec = times[0].tv_nsec;
>  			newattrs.ia_valid |= ATTR_ATIME_SET;
>  		}
>  
>  		if (times[1].tv_nsec == UTIME_OMIT)
>  			newattrs.ia_valid &= ~ATTR_MTIME;
>  		else if (times[1].tv_nsec != UTIME_NOW) {
> -			newattrs.ia_mtime.tv_sec = times[1].tv_sec;
> -			newattrs.ia_mtime.tv_nsec = times[1].tv_nsec;
> +			newattrs.ia_mtime.tv_sec =
> +				clamp(times[1].tv_sec, sb->s_time_min, sb->s_time_max);
> +			if (times[1].tv_sec >= sb->s_time_max || times[1].tv_sec == sb->s_time_min)

Line length.

Also, didn't you just introduce a function to clamp tv_sec and fix
granularity?  Why not just use it here?  I think this is the third time
I've seen this open-coded logic.

--D

> +				newattrs.ia_mtime.tv_nsec = 0;
> +			else
> +				newattrs.ia_mtime.tv_nsec = times[1].tv_nsec;
>  			newattrs.ia_valid |= ATTR_MTIME_SET;
>  		}
>  		/*
> -- 
> 2.17.1
>