Re: [PATCH bpf-next v3 2/4] selftests/bpf: Update EFAULT {g,s}etsockopt selftests

[Martin KaFai Lau <martin.lau@xxxxxxxxx>]

On 5/2/23 5:29 PM, Martin KaFai Lau wrote:
> On 5/1/23 12:48 PM, Stanislav Fomichev wrote:
> > Instead of assuming EFAULT, let's assume the BPF program's
> > output is ignored.
> >
> > Remove "getsockopt: deny arbitrary ctx->retval" because it
> > was actually testing optlen. We have separate set of tests
> > for retval.
> >
> > Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> > ---
> >   .../selftests/bpf/prog_tests/sockopt.c        | 98 +++++++++++++++++--
> >   1 file changed, 92 insertions(+), 6 deletions(-)
> >
> > diff --git a/tools/testing/selftests/bpf/prog_tests/sockopt.c 
> > b/tools/testing/selftests/bpf/prog_tests/sockopt.c
> > index aa4debf62fc6..a7bc9dc93ce0 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/sockopt.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/sockopt.c
> > @@ -5,6 +5,10 @@
> >   static char bpf_log_buf[4096];
> >   static bool verbose;
> > +#ifndef PAGE_SIZE
> > +#define PAGE_SIZE 4096
> > +#endif
> > +
> >   enum sockopt_test_error {
> >       OK = 0,
> >       DENY_LOAD,
> > @@ -273,10 +277,30 @@ static struct sockopt_test {
> >           .error = EFAULT_GETSOCKOPT,
> >       },
> >       {
> > -        .descr = "getsockopt: deny arbitrary ctx->retval",
> > +        .descr = "getsockopt: ignore >PAGE_SIZE optlen",
> >           .insns = {
> > -            /* ctx->retval = 123 */
> > -            BPF_MOV64_IMM(BPF_REG_0, 123),
> > +            /* write 0xFF to the first optval byte */
> > +
> > +            /* r6 = ctx->optval */
> > +            BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1,
> > +                    offsetof(struct bpf_sockopt, optval)),
> > +            /* r2 = ctx->optval */
> > +            BPF_MOV64_REG(BPF_REG_2, BPF_REG_6),
> > +            /* r6 = ctx->optval + 1 */
> > +            BPF_ALU64_IMM(BPF_ADD, BPF_REG_6, 1),
> > +
> > +            /* r7 = ctx->optval_end */
> > +            BPF_LDX_MEM(BPF_DW, BPF_REG_7, BPF_REG_1,
> > +                    offsetof(struct bpf_sockopt, optval_end)),
> > +
> > +            /* if (ctx->optval + 1 <= ctx->optval_end) { */
> > +            BPF_JMP_REG(BPF_JGT, BPF_REG_6, BPF_REG_7, 1),
> > +            /* ctx->optval[0] = 0xF0 */
> > +            BPF_ST_MEM(BPF_B, BPF_REG_2, 0, 0xFF),
> > +            /* } */
> > +
> > +            /* ctx->retval = 0 */
> > +            BPF_MOV64_IMM(BPF_REG_0, 0),
>
>
> This is an interesting test case. One more question just came to my mind,
> does it make sense to also ignore the bpf-prog's 'ctx->retval = 0' in getsockopt 
> considering its optval change has already been ignored. Something like:
>
>      if (optval && (ctx.optlen > max_optlen || ctx.optlen < 0)) {
>          if (orig_optlen > PAGE_SIZE && ctx.optlen >= 0) {
>              pr_info_once("bpf getsockopt: ignoring program buffer with 
> optlen=%d (max_optlen=%d)\n",
>                       ctx.optlen, max_optlen);
>              ret = retval;
>                          goto out;
>                  }
>                  ret = -EFAULT;
>                  goto out;
>          }

Previous one has indentation off. Meaning to be:

	if (optval && (ctx.optlen > max_optlen || ctx.optlen < 0)) {
		if (orig_optlen > PAGE_SIZE && ctx.optlen >= 0) {
			pr_info_once("bpf getsockopt: ignoring program buffer with optlen=%d 
(max_optlen=%d)\n",
				     ctx.optlen, max_optlen);
			ret = retval;
			goto out;
		}
		ret = -EFAULT;
		goto out;
	}

> >               BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
> >                       offsetof(struct bpf_sockopt, retval)),
> > @@ -287,9 +311,10 @@ static struct sockopt_test {
> >           .attach_type = BPF_CGROUP_GETSOCKOPT,
> >           .expected_attach_type = BPF_CGROUP_GETSOCKOPT,
> > -        .get_optlen = 64,
> > -
> > -        .error = EFAULT_GETSOCKOPT,
> > +        .get_level = 1234,
> > +        .get_optname = 5678,
> > +        .get_optval = {}, /* the changes are ignored */
> > +        .get_optlen = PAGE_SIZE + 1,
> >           }
> > +        if (optlen > sizeof(test->get_optval))
> > +            optlen = sizeof(test->get_optval);
> > +
> >           if (memcmp(optval, test->get_optval, optlen) != 0) {
> >               errno = 0;
> >               log_err("getsockopt returned unexpected optval");