linux-kernel - Re: [PATCH] utimensat() non-conformances and fixes

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Date:	Wed, 23 Apr 2008 11:37:04 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	mtk.manpages@...glemail.com
CC:	linux-fsdevel@...r.kernel.org, drepper@...hat.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-man@...r.kernel.org
Subject: Re: [PATCH] utimensat() non-conformances and fixes

[Please, please, please always CC linux-fsdevel on VFS related work.
It's even in MAINTAINERS now]

> --- linux-2.6.25-rc6-orig/fs/utimes.c	2008-04-07 22:25:08.000000000 +0200
> +++ linux-2.6.25-rc6/fs/utimes.c	2008-04-07 23:57:41.000000000 +0200
> @@ -95,27 +95,37 @@
> 
>  	/* Don't worry, the checks are done in inode_change_ok() */
>  	newattrs.ia_valid = ATTR_CTIME | ATTR_MTIME | ATTR_ATIME;
> -	if (times) {
> +	if (times && ! ((times[0].tv_nsec == UTIME_NOW &&
> +			 times[1].tv_nsec == UTIME_NOW) ||
> +			(times[0].tv_nsec == UTIME_OMIT &&
> +			 times[1].tv_nsec == UTIME_OMIT))) {
>  		error = -EPERM;
>                  if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
>                          goto dput_and_out;
> 
> -		if (times[0].tv_nsec == UTIME_OMIT)
> -			newattrs.ia_valid &= ~ATTR_ATIME;
> -		else if (times[0].tv_nsec != UTIME_NOW) {
> +		if (times[0].tv_nsec == UTIME_OMIT) {
> +			newattrs.ia_atime = inode->i_atime;
> +			newattrs.ia_valid |= ATTR_ATIME_SET;

This seems wrong.  Why exactly was this change made?

Setting the time to inode->i_atime is *not* the same as not setting
the time.  For some filesystems i_atime is just a cached value, that
may or may not match the actual last access time.  For those
filesystems this could have very strange effects.

> +		} 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_valid |= ATTR_ATIME_SET;
>  		}
> 
> -		if (times[1].tv_nsec == UTIME_OMIT)
> -			newattrs.ia_valid &= ~ATTR_MTIME;
> -		else if (times[1].tv_nsec != UTIME_NOW) {
> +		if (times[1].tv_nsec == UTIME_OMIT) {
> +			newattrs.ia_mtime = inode->i_mtime;
> +			newattrs.ia_valid |= ATTR_MTIME_SET;

Ditto.

> +		} 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_valid |= ATTR_MTIME_SET;
>  		}
> +
> +	} else if (unlikely(times && times[0].tv_nsec == UTIME_OMIT &&
> +			times[1].tv_nsec == UTIME_OMIT)) {
> +		newattrs.ia_valid &= ~(ATTR_ATIME | ATTR_MTIME | ATTR_CTIME);

So this is a no-op?  In which case this check could be moved to the
top of the function to just return zero.

Miklos

>  	} else {
> +		/* times is NULL, or both tv_nsec fields are UTIME_NOW */
>  		error = -EACCES;
>                  if (IS_IMMUTABLE(inode))
>                          goto dput_and_out;
> @@ -150,14 +160,6 @@
>  	if (utimes) {
>  		if (copy_from_user(&tstimes, utimes, sizeof(tstimes)))
>  			return -EFAULT;
> -		if ((tstimes[0].tv_nsec == UTIME_OMIT ||
> -		     tstimes[0].tv_nsec == UTIME_NOW) &&
> -		    tstimes[0].tv_sec != 0)
> -			return -EINVAL;
> -		if ((tstimes[1].tv_nsec == UTIME_OMIT ||
> -		     tstimes[1].tv_nsec == UTIME_NOW) &&
> -		    tstimes[1].tv_sec != 0)
> -			return -EINVAL;
> 
>  		/* Nothing to do, we must not even check the path.  */
>  		if (tstimes[0].tv_nsec == UTIME_OMIT &&
> 
> 
> ==================================================
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