linux-kernel - Re: [parch 3/4] vfs: utimensat(): fix error checking for {UTIME_NOW,UTIME

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Message-Id: <E1K3kkj-0007gR-Pb@pomaz-ex.szeredi.hu>
Date:	Wed, 04 Jun 2008 06:37:37 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	mtk.manpages@...glemail.com
CC:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	hch@....de, miklos@...redi.hu, viro@...iv.linux.org.uk,
	jamie@...reable.org, drepper@...hat.com,
	linux-fsdevel@...r.kernel.org, subrata@...ux.vnet.ibm.com
Subject: Re: [parch 3/4] vfs: utimensat(): fix error checking for {UTIME_NOW,UTIME_OMIT}
 case

> The POSIX.1 draft spec for utimensat() says that to do anything
> other than setting both timestamps to a time other than the
> current time (i.e., times is not NULL, and both tv_nsec fields
> are not UTIME_NOW and both tv_nsec fields are not UTIME_OMIT),
> either:
> 
> a) the caller's effective user ID must match the file owner; or
> b) the caller must have appropriate privileges.
> 
> If this condition is violated, then the error EPERM should result.
> However, the current implementation does not generate EPERM if
> one tv_nsec field is UTIME_NOW while the other is UTIME_OMIT.
> It should give this error for that case.
> 
> This patch:
> 
> a) Repairs that problem.
> b) Removes the now unneeded nsec_special() helper function.
> 
> Miklos suggested an alternative idea, migrating the
> is_owner_or_cap() checks into fs/attr.c:inode_change_ok() via
> the use of an ATTR_OWNER_CHECK flag.  Maybe we could do that
> later, but for now I've gone with this version, which is
> simpler, and can be more easily read as being correct.

Wise decision.

> CC: Miklos Szeredi <miklos@...redi.hu>
> CC: Al Viro <viro@...iv.linux.org.uk>
> CC: Ulrich Drepper <drepper@...hat.com>
> Signed-off-by: Michael Kerrisk <mtk.manpages@...il.com>
> 
> 
> --- linux-2.6.26-rc4/fs/utimes.c	2008-06-03 23:11:53.000000000 +0200
> +++ linux-2.6.26-rc4-utimensat-fix-v4/fs/utimes.c	2008-06-03 23:04:48.000000000 +0200
> @@ -40,14 +40,9 @@
> 
>  #endif
> 
> -static bool nsec_special(long nsec)
> -{
> -	return nsec == UTIME_OMIT || nsec == UTIME_NOW;
> -}
> -
>  static bool nsec_valid(long nsec)
>  {
> -	if (nsec_special(nsec))
> +	if (nsec == UTIME_OMIT || nsec == UTIME_NOW)
>  		return true;
> 
>  	return nsec >= 0 && nsec <= 999999999;
> @@ -135,8 +130,7 @@
>  	 * UTIME_NOW, then need to check permissions, because
>  	 * inode_change_ok() won't do it.
>  	 */
> -	if (!times || (nsec_special(times[0].tv_nsec) &&
> -		       nsec_special(times[1].tv_nsec))) {
> +	if (!times) {

This can be restored to be the "else" branch of the "if (times)".

>  		error = -EACCES;
>                  if (IS_IMMUTABLE(inode))
>  			goto mnt_drop_write_and_out;
> @@ -151,6 +145,18 @@
>  					goto mnt_drop_write_and_out;
>  			}
>  		}
> +	} else if ((times[0].tv_nsec == UTIME_NOW &&
> +		    times[1].tv_nsec == UTIME_OMIT)
> +		  ||
> +		   (times[0].tv_nsec == UTIME_OMIT &&
> +		    times[1].tv_nsec == UTIME_NOW)) {

And I'd rather put this inside the "if (times)" for clarity.

> +		error =-EPERM;
> +
> +		if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
> +			goto mnt_drop_write_and_out;

And then you would've realized, that this check was already done.

> +
> +		if (!is_owner_or_cap(inode))
> +			goto mnt_drop_write_and_out;

OK.

>  	}
>  	mutex_lock(&inode->i_mutex);
>  	error = notify_change(dentry, &newattrs);
> 
> 
> 
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