Subject: Re: [PATCH net 1/2] net: sctp: sctp_auth_make_key_vector: fix undefined ref-count behaviour

From: Daniel Borkmann <[email-masked]>
Date: Thu, 07 Feb 2013 16:24:53 +0100

On 02/07/2013 04:04 PM, Vlad Yasevich wrote:
> On 02/07/2013 05:55 AM, Daniel Borkmann wrote:
>> In sctp_auth_make_key_vector(), a sctp_auth_bytes structure is being
>> allocated, but without setting its object reference count, thus it's
>> initialized with a random value from the memory, which can lead to
>> i) premature free's of this object when being put (with possible
>> subsequent kernel panics), or ii) memory leaks when refcount has a
>> high value.
>>
>> Fix this by using the appropriate sctp_auth_create_key() allocator,
>> which performs sanity checks, sets length and the refcount, as similar
>> done in sctp_auth_asoc_set_secret() and others. This bug seems to be
>> present since 2007 (1f485649f529: Implement SCTP-AUTH internals).
>
> Not strictly a bug.  The vectors are temporary and directly freed by the caller.   They are only used by sctp_auth_asoc_create_secret() which builds the association secret key.  The vectors are destroyed at the end of that function using kfree() thus noone really cares about
> the refcount on them and there are no leaks.
>
> If you are going to convert to using sctp_auth_create_key() then you
> need to convert the callers to user to use sctp_auth_key_put(). Otherwise you are leaking object counts.

Thanks for your feedback!

If Dave is okay with this, then:

  - [PATCH net 2/2] net: sctp: sctp_auth_key_put: use kzfree instead of kfree
  - [PATCH net-next] net: sctp: sctp_auth_make_key_vector: remove duplicate ntohs calls

can be applied as is. (If necessary, I could send the first one _unchanged_ as a
single patch again, since it was part of a patchset. However, it will apply
cleanly as we have it right here.)

Then, to avoid any future confusion and to stay consistent, I'll convert this
to sctp_auth_create_key() API as well and make use of the sctp_auth_key_put()
in a later possible patch *after* those two have been applied.

>> Signed-off-by: Daniel Borkmann <[email-masked]>
>> ---
>>   net/sctp/auth.c | 4 +---
>>   1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/net/sctp/auth.c b/net/sctp/auth.c
>> index 159b9bc..55f1b06 100644
>> --- a/net/sctp/auth.c
>> +++ b/net/sctp/auth.c
>> @@ -205,12 +205,10 @@ static struct sctp_auth_bytes *sctp_auth_make_key_vector(
>>           if (chunks)
>>           len += ntohs(chunks->param_hdr.length);
>>
>> -    new = kmalloc(sizeof(struct sctp_auth_bytes) + len, gfp);
>> +    new = sctp_auth_create_key(len, gfp);
>>       if (!new)
>>           return NULL;
>>
>> -    new->len = len;
>> -
>>       memcpy(new->data, random, ntohs(random->param_hdr.length));
>>       offset += ntohs(random->param_hdr.length);
>>
>>
>