Re: [parch 3/4] vfs: utimensat(): fix error checking for {UTIME_NOW,UTIME_OMIT} case

["Michael Kerrisk" <mtk.manpages@googlemail.com>]

On Wed, Jun 4, 2008 at 6:37 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
>> 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@szeredi.hu>
>> CC: Al Viro <viro@zeniv.linux.org.uk>
>> CC: Ulrich Drepper <drepper@redhat.com>
>> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.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)".

Yes.  Thanks.

>>               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.

Yes.

>
>> +             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.

Quite!

I'll make these changes and test.

Cheers,

Michael

>> +
>> +             if (!is_owner_or_cap(inode))
>> +                     goto mnt_drop_write_and_out;
>
> OK.
>
>>       }
>>       mutex_lock(&inode->i_mutex);
>>       error = notify_change(dentry, &newattrs);
>>
>>
>>
>



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html