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

[Simon Horman]

On Sat, May 27, 2023 at 07:49:26AM +0000, Ashwin Dayanand Kamat wrote:
> 
> 
> > 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?

Hi Ashwin,

I don't recall exactly what I was thinking 2 months ago.
But looking at this a second time it seems that I may have misread your
patch: I now have no objections to it in its original form.