Re: [PATCH] fs: switch order of CAP_DAC_OVERRIDE and CAP_DAC_READ_SEARCH checks

[John Johansen <john.johansen@canonical.com>]

On 03/10/2017 11:54 AM, Paul Moore wrote:
> On Fri, Mar 10, 2017 at 12:14 PM, Stephen Smalley <sds@tycho.nsa.gov> wrote:
>> generic_permission() presently checks CAP_DAC_OVERRIDE prior to
>> CAP_DAC_READ_SEARCH.  This can cause misleading audit messages when
>> using a LSM such as SELinux or AppArmor, since CAP_DAC_OVERRIDE
>> may not be required for the operation.  Flip the order of the
>> tests so that CAP_DAC_OVERRIDE is only checked when required for
>> the operation.
>>
>> Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
>> ---
>>  fs/namei.c | 20 ++++++++++----------
>>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> This is the second posting of this patch and so far no comment ... if
> I don't see any negative responses by next week I'll go ahead and
> merge this into the selinux/next tree.
> 
sounds good to me, the patch looks good you can have my acked-by for how
this affects apparmor, or hrmm should that be a reviewed-by for the vfs
end

Acked-by: John Johansen <john.johansen@canonical.com>

>> diff --git a/fs/namei.c b/fs/namei.c
>> index d41fab7..482414a 100644
>> --- a/fs/namei.c
>> +++ b/fs/namei.c
>> @@ -340,22 +340,14 @@ int generic_permission(struct inode *inode, int mask)
>>
>>         if (S_ISDIR(inode->i_mode)) {
>>                 /* DACs are overridable for directories */
>> -               if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE))
>> -                       return 0;
>>                 if (!(mask & MAY_WRITE))
>>                         if (capable_wrt_inode_uidgid(inode,
>>                                                      CAP_DAC_READ_SEARCH))
>>                                 return 0;
>> -               return -EACCES;
>> -       }
>> -       /*
>> -        * Read/write DACs are always overridable.
>> -        * Executable DACs are overridable when there is
>> -        * at least one exec bit set.
>> -        */
>> -       if (!(mask & MAY_EXEC) || (inode->i_mode & S_IXUGO))
>>                 if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE))
>>                         return 0;
>> +               return -EACCES;
>> +       }
>>
>>         /*
>>          * Searching includes executable on directories, else just read.
>> @@ -364,6 +356,14 @@ int generic_permission(struct inode *inode, int mask)
>>         if (mask == MAY_READ)
>>                 if (capable_wrt_inode_uidgid(inode, CAP_DAC_READ_SEARCH))
>>                         return 0;
>> +       /*
>> +        * Read/write DACs are always overridable.
>> +        * Executable DACs are overridable when there is
>> +        * at least one exec bit set.
>> +        */
>> +       if (!(mask & MAY_EXEC) || (inode->i_mode & S_IXUGO))
>> +               if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE))
>> +                       return 0;
>>
>>         return -EACCES;
>>  }
>> --
>> 2.7.4
>>
> 
> 
>