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

[Ashwin Dayanand Kamat]

> On 23-Mar-2023, at 2:16 AM, Simon Horman <simon.horman@xxxxxxxxxxxx> wrote:
> 
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> 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

>> + 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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