On Thu, Jul 7, 2022 at 3:09 PM Martin KaFai Lau <kafai@xxxxxx> wrote:
>
> On Thu, Jul 07, 2022 at 12:18:33PM -0700, sdf@xxxxxxxxxx wrote:
> > On 07/07, Martin KaFai Lau wrote:
> > > On Thu, Jul 07, 2022 at 09:02:33AM -0700, Stanislav Fomichev wrote:
> > > > Syzkaller reports the following crash:
> > > > RIP: 0010:check_return_code kernel/bpf/verifier.c:10575 [inline]
> > > > RIP: 0010:do_check kernel/bpf/verifier.c:12346 [inline]
> > > > RIP: 0010:do_check_common+0xb3d2/0xd250 kernel/bpf/verifier.c:14610
> > > >
> > > > With the following reproducer:
> > > > bpf$PROG_LOAD_XDP(0x5, &(0x7f00000004c0)={0xd, 0x3,
> > > &(0x7f0000000000)=ANY=[@ANYBLOB="1800000000000019000000000000000095"],
> > > &(0x7f0000000300)='GPL\x00', 0x0, 0x0, 0x0, 0x0, 0x0, '\x00', 0x0, 0x2b,
> > > 0xffffffffffffffff, 0x8, 0x0, 0x0, 0x10, 0x0}, 0x80)
> > > >
> > > > Because we don't enforce expected_attach_type for XDP programs,
> > > > we end up in hitting 'if (prog->expected_attach_type == BPF_LSM_CGROUP'
> > > > part in check_return_code and follow up with testing
> > > > `prog->aux->attach_func_proto->type`, but `prog->aux->attach_func_proto`
> > > > is NULL.
> > > >
> > > > Add explicit prog_type check for the "Note, BPF_LSM_CGROUP that
> > > > attach ..." condition. Also, don't skip return code check for
> > > > LSM/STRUCT_OPS.
> > > >
> > > > The above actually brings an issue with existing selftest which
> > > > tries to return EPERM from void inet_csk_clone. Fix the
> > > > test (and move called_socket_clone to make sure it's not
> > > > incremented in case of an error) and add a new one to explicitly
> > > > verify this condition.
> > > >
> > > > v2:
> > > > - Martin: don't add new helper, check prog_type instead
> > > > - Martin: check expected_attach_type as well at the function entry
> > > > - Update selftest to verify this condition
> > > >
> > > > Fixes: 69fd337a975c ("bpf: per-cgroup lsm flavor")
> > > > Reported-by: syzbot+5cc0730bd4b4d2c5f152@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > > Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> > > > ---
> > > > kernel/bpf/verifier.c | 2 ++
> > > > .../testing/selftests/bpf/prog_tests/lsm_cgroup.c | 12 ++++++++++++
> > > > tools/testing/selftests/bpf/progs/lsm_cgroup.c | 12 ++++++------
> > > > .../selftests/bpf/progs/lsm_cgroup_nonvoid.c | 14 ++++++++++++++
> > > > 4 files changed, 34 insertions(+), 6 deletions(-)
> > > > create mode 100644
> > > tools/testing/selftests/bpf/progs/lsm_cgroup_nonvoid.c
> > > >
> > > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > > > index df3ec6b05f05..2bc1e7252778 100644
> > > > --- a/kernel/bpf/verifier.c
> > > > +++ b/kernel/bpf/verifier.c
> > > > @@ -10445,6 +10445,7 @@ static int check_return_code(struct
> > > bpf_verifier_env *env)
> > > >
> > > > /* LSM and struct_ops func-ptr's return type could be "void" */
> > > > if (!is_subprog &&
> > > > + prog->expected_attach_type != BPF_LSM_CGROUP &&
> > > BPF_PROG_TYPE_STRUCT_OPS also uses the expected_attach_type,
> > > so the expected_attach_type check should only be done for LSM prog alone.
> > > Others lgtm.
> >
> > In this case, something like the following should be sufficient?
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 2bc1e7252778..6702a5fc12e6 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -10445,11 +10445,13 @@ static int check_return_code(struct
> > bpf_verifier_env *env)
> >
> > /* LSM and struct_ops func-ptr's return type could be "void" */
> > if (!is_subprog &&
> > - prog->expected_attach_type != BPF_LSM_CGROUP &&
> > - (prog_type == BPF_PROG_TYPE_STRUCT_OPS ||
> > - prog_type == BPF_PROG_TYPE_LSM) &&
> > - !prog->aux->attach_func_proto->type)
> > - return 0;
> > + !prog->aux->attach_func_proto->type) {
> prog_type check has to be done first since prog->aux->attach_func_proto
> depends on the prog_type.
>
> How about a small tweak on top of yours ?
Looks good, thanks! Will test and resend sometime tomorrow.
> /* LSM and struct_ops func-ptr's return type could be "void" */
> if (!is_subprog) {
> switch (prog_type) {
> case BPF_PROG_TYPE_LSM:
> if (prog->expected_attach_type == BPF_LSM_CGROUP)
> /* cgroup prog needs to return 0 or 1 */
> break;
> fallthrough;
> case BPF_PROG_TYPE_STRUCT_OPS:
> if (!prog->aux->attach_func_proto->type)
> return 0;
> break;
> default:
> break;
> }
> }
>
> > + if (prog_type == BPF_PROG_TYPE_STRUCT_OPS)
> > + return 0;
> > + if (prog_type == BPF_PROG_TYPE_LSM &&
> > + prog->expected_attach_type != BPF_LSM_CGROUP)
> > + return 0;
> > + }
> >
> > /* eBPF calling convention is such that R0 is used
> > * to return the value from eBPF program.
> >
> > > > (prog_type == BPF_PROG_TYPE_STRUCT_OPS ||
> > > > prog_type == BPF_PROG_TYPE_LSM) &&
> > > > !prog->aux->attach_func_proto->type)
> > > > @@ -10572,6 +10573,7 @@ static int check_return_code(struct
> > > bpf_verifier_env *env)
> > > > if (!tnum_in(range, reg->var_off)) {
> > > > verbose_invalid_scalar(env, reg, &range, "program exit", "R0");
> > > > if (prog->expected_attach_type == BPF_LSM_CGROUP &&
> > > > + prog_type == BPF_PROG_TYPE_LSM &&
> > > > !prog->aux->attach_func_proto->type)
> > > > verbose(env, "Note, BPF_LSM_CGROUP that attach to void LSM hooks
> > > can't modify return value!\n");
> > > > return -EINVAL;
