Re: [PATCH v2] net/sctp: Make sha1 as default algorithm if fips is enabled

[Ashwin Dayanand Kamat]

> On 25-Mar-2023, at 12:03 PM, Ashwin Dayanand Kamat <kashwindayan@xxxxxxxxxx> wrote:
> 
> 
>> On 23-Mar-2023, at 2:16 AM, Simon Horman <simon.horman@xxxxxxxxxxxx> wrote:
>> 
>> !! External Email
>> 
>> On Wed, Mar 22, 2023 at 07:34:40PM +0530, Ashwin Dayanand Kamat wrote:
>>> MD5 is not FIPS compliant. But still md5 was used as the default
>>> algorithm for sctp if fips was enabled.
>>> Due to this, listen() system call in ltp tests was failing for sctp
>>> in fips environment, with below error message.
>>> 
>>> [ 6397.892677] sctp: failed to load transform for md5: -2
>>> 
>>> Fix is to not assign md5 as default algorithm for sctp
>>> if fips_enabled is true. Instead make sha1 as default algorithm.
>>> 
>>> Fixes: ltp testcase failure "cve-2018-5803 sctp_big_chunk"
>>> Signed-off-by: Ashwin Dayanand Kamat <kashwindayan@xxxxxxxxxx>
>>> ---
>>> v2:
>>> the listener can still fail if fips mode is enabled after
>>> that the netns is initialized. So taking action in sctp_listen_start()
>>> and buming a ratelimited notice the selected hmac is changed due to fips.
>>> ---
>>> net/sctp/socket.c | 10 ++++++++++
>>> 1 file changed, 10 insertions(+)
>>> 
>>> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
>>> index b91616f819de..a1107f42869e 100644
>>> --- a/net/sctp/socket.c
>>> +++ b/net/sctp/socket.c
>>> @@ -49,6 +49,7 @@
>>> #include <linux/poll.h>
>>> #include <linux/init.h>
>>> #include <linux/slab.h>
>>> +#include <linux/fips.h>
>>> #include <linux/file.h>
>>> #include <linux/compat.h>
>>> #include <linux/rhashtable.h>
>>> @@ -8496,6 +8497,15 @@ static int sctp_listen_start(struct sock *sk, int backlog)
>>> struct crypto_shash *tfm = NULL;
>>> char alg[32];
>>> 
>>> + if (fips_enabled && !strcmp(sp->sctp_hmac_alg, "md5")) {
>>> +#if (IS_ENABLED(CONFIG_SCTP_DEFAULT_COOKIE_HMAC_SHA1))
>> 
>> I'm probably misunderstanding things, but would
>> IS_ENABLED(CONFIG_SCTP_COOKIE_HMAC_SHA1)
>> be more appropriate here?
>> 
> 
> Hi Simon,
> I have moved the same check from sctp_init() to here based on the review for v1 patch.
> Please let me know if there is any alternative which can be used?
> 
> Thanks,
> Ashwin Kamat
> 
Hi Team,
Any update on this?

Thanks,
Ashwin Kamat
>>> + sp->sctp_hmac_alg = "sha1";
>>> +#else
>>> + sp->sctp_hmac_alg = NULL;
>>> +#endif
>>> + net_info_ratelimited("changing the hmac algorithm, as md5 is not supported when fips is enabled");
>>> + }
>>> +
>>> /* Allocate HMAC for generating cookie. */
>>> if (!sp->hmac && sp->sctp_hmac_alg) {
>>> sprintf(alg, "hmac(%s)", sp->sctp_hmac_alg);
>>> --
>>> 2.39.0
>>> 
>> 
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> 
> 
> 
> 
>