Re: [PATCH][next] KEYS: trusted: Fix missing null return from kzalloc call

[Sumit Garg <sumit.garg@linaro.org>]

On Mon, 12 Apr 2021 at 22:34, Colin Ian King <colin.king@canonical.com> wrote:
>
> On 12/04/2021 17:48, James Bottomley wrote:
> > On Mon, 2021-04-12 at 17:01 +0100, Colin King wrote:
> >> From: Colin Ian King <colin.king@canonical.com>
> >>
> >> The kzalloc call can return null with the GFP_KERNEL flag so
> >> add a null check and exit via a new error exit label. Use the
> >> same exit error label for another error path too.
> >>
> >> Addresses-Coverity: ("Dereference null return value")
> >> Fixes: 830027e2cb55 ("KEYS: trusted: Add generic trusted keys
> >> framework")
> >> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> >> ---
> >>  security/keys/trusted-keys/trusted_core.c | 6 ++++--
> >>  1 file changed, 4 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/security/keys/trusted-keys/trusted_core.c
> >> b/security/keys/trusted-keys/trusted_core.c
> >> index ec3a066a4b42..90774793f0b1 100644
> >> --- a/security/keys/trusted-keys/trusted_core.c
> >> +++ b/security/keys/trusted-keys/trusted_core.c
> >> @@ -116,11 +116,13 @@ static struct trusted_key_payload
> >> *trusted_payload_alloc(struct key *key)
> >>
> >>      ret = key_payload_reserve(key, sizeof(*p));
> >>      if (ret < 0)
> >> -            return p;
> >> +            goto err;
> >>      p = kzalloc(sizeof(*p), GFP_KERNEL);
> >> +    if (!p)
> >> +            goto err;
> >>
> >>      p->migratable = migratable;
> >> -
> >> +err:
> >>      return p;
> >
> > This is clearly a code migration bug in
> >
> > commit 251c85bd106099e6f388a89e88e12d14de2c9cda
> > Author: Sumit Garg <sumit.garg@linaro.org>
> > Date:   Mon Mar 1 18:41:24 2021 +0530
> >
> >     KEYS: trusted: Add generic trusted keys framework
> >
> > Which has for addition to trusted_core.c:
> >
> > +static struct trusted_key_payload *trusted_payload_alloc(struct key
> > *key)
> > +{
> > +       struct trusted_key_payload *p = NULL;
> > +       int ret;
> > +
> > +       ret = key_payload_reserve(key, sizeof(*p));
> > +       if (ret < 0)
> > +               return p;
> > +       p = kzalloc(sizeof(*p), GFP_KERNEL);
> > +
> > +       p->migratable = migratable;
> > +
> > +       return p;
> > +}
> >
> > And for trusted_tpm1.c:
> >
> > -static struct trusted_key_payload *trusted_payload_alloc(struct key
> > *key)
> > -{
> > -       struct trusted_key_payload *p = NULL;
> > -       int ret;
> > -
> > -       ret = key_payload_reserve(key, sizeof *p);
> > -       if (ret < 0)
> > -               return p;
> > -       p = kzalloc(sizeof *p, GFP_KERNEL);
> > -       if (p)
> > -               p->migratable = 1; /* migratable by default */
> > -       return p;
> > -}
> >
> > The trusted_tpm1.c code was correct and we got this bug introduced by
> > what should have been a simple cut and paste ... how did that happen?

It was a little more than just cut and paste where I did generalized
"migratable" flag to be provided by the corresponding trust source's
ops struct.

> > And therefore, how safe is the rest of the extraction into
> > trusted_core.c?
> >
>
> fortunately it gets caught by static analysis, but it does make me also
> concerned about what else has changed and how this gets through review.
>

I agree that extraction into trusted_core.c was a complex change but
this patch has been up for review for almost 2 years [1]. And
extensive testing can't catch this sort of bug as allocation wouldn't
normally fail.

[1] https://lwn.net/Articles/795416/

-Sumit

> > James
> >
> >
>