[patch] cifs: integer overflow in parse_dacl()

[Steve French]

We could calculate max_aces based on a minimum sized ace and maximum
smb frame size (which would be 64K presumably for Windows for
non-Writes, but larger for Samba), but not sure if it is worth the
trouble unless you find a path where we would parse beyond end of
frame,

On Wed, Jan 11, 2012 at 12:20 PM, Jeff Layton <jlayton at samba.org> wrote:
> On Wed, 11 Jan 2012 11:24:03 -0600
> Steve French <smfrench at gmail.com> wrote:
>
>> On Wed, Jan 11, 2012 at 9:50 AM, Shirish Pargaonkar
>> <shirishpargaonkar at gmail.com> wrote:
>> > On Wed, Jan 11, 2012 at 1:46 AM, Dan Carpenter <dan.carpenter at oracle.com> wrote:
>> >> On 32 bit systems num_aces * sizeof(struct cifs_ace *) could overflow
>> >> leading to a smaller ppace buffer than we expected.
>> >>
>> >> Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
>> >>
>> >> diff --git a/fs/cifs/cifsacl.c b/fs/cifs/cifsacl.c
>> >> index 72ddf23..c1b2544 100644
>> >> --- a/fs/cifs/cifsacl.c
>> >> +++ b/fs/cifs/cifsacl.c
>> >> @@ -909,6 +909,8 @@ static void parse_dacl(struct cifs_acl *pdacl, char *end_of_acl,
>> >>                umode_t group_mask = S_IRWXG;
>> >>                umode_t other_mask = S_IRWXU | S_IRWXG | S_IRWXO;
>> >>
>> >> +               if (num_aces > ULONG_MAX / sizeof(struct cifs_ace *))
>> >
>> > Should an error/warning (like cifs client can't handle these many aces or
>> > possible erroneous number of aces sent by server etc.) be logged before
>> > returning?
>> >
>> >> +                       return;
>> >>                ppace = kmalloc(num_aces * sizeof(struct cifs_ace *),
>> >>                                GFP_KERNEL);
>> >>                if (!ppace) {
>>
>> Perhaps.   Also note that you would overflow maximum smb size if num
>> aces is huge
>> so would you have even gotten this far?
>>
>
> Only if the smb frame is properly formed. It's possible that it's
> corrupt in such a way that the num_aces field is much larger than it
> should be, but the rest of the frame looks OK.
>
> --
> Jeff Layton <jlayton at samba.org>



-- 
Thanks,

Steve