selftests/bpf: add missing netfilter return value and ctx access tests

Extend prog_tests with two test cases:

 # ./test_progs --allow=verifier_netfilter_retcode
 #278/1   verifier_netfilter_retcode/bpf_exit with invalid return code. test1:OK
 #278/2   verifier_netfilter_retcode/bpf_exit with valid return code. test2:OK
 #278/3   verifier_netfilter_retcode/bpf_exit with valid return code. test3:OK
 #278/4   verifier_netfilter_retcode/bpf_exit with invalid return code. test4:OK
 #278     verifier_netfilter_retcode:OK

This checks that only accept and drop (0,1) are permitted.

NF_QUEUE could be implemented later if we can guarantee that attachment
of such programs can be rejected if they get attached to a pf/hook that
doesn't support async reinjection.

NF_STOLEN could be implemented via trusted helpers that can guarantee
that the skb will eventually be free'd.

v4: test case for bpf_nf_ctx access checks, requested by Alexei Starovoitov.
v5: also check ctx->{state,skb} can be dereferenced (Alexei).

 # ./test_progs --allow=verifier_netfilter_ctx
 #281/1   verifier_netfilter_ctx/netfilter invalid context access, size too short:OK
 #281/2   verifier_netfilter_ctx/netfilter invalid context access, size too short:OK
 #281/3   verifier_netfilter_ctx/netfilter invalid context access, past end of ctx:OK
 #281/4   verifier_netfilter_ctx/netfilter invalid context, write:OK
 #281/5   verifier_netfilter_ctx/netfilter valid context read and invalid write:OK
 #281/6   verifier_netfilter_ctx/netfilter test prog with skb and state read access:OK
 #281/7   verifier_netfilter_ctx/netfilter test prog with skb and state read access @unpriv:OK
 #281     verifier_netfilter_ctx:OK
Summary: 1/7 PASSED, 0 SKIPPED, 0 FAILED

This checks:
1/2: partial reads of ctx->{skb,state} are rejected
3. read access past sizeof(ctx) is rejected
4. write to ctx content, e.g. 'ctx->skb = NULL;' is rejected
5. ctx->state content cannot be altered
6. ctx->state and ctx->skb can be dereferenced
7. ... same program fails for unpriv (CAP_NET_ADMIN needed).

Link: https://lore.kernel.org/bpf/20230419021152.sjq4gttphzzy6b5f@dhcp-172-26-102-232.dhcp.thefacebook.com/
Link: https://lore.kernel.org/bpf/20230420201655.77kkgi3dh7fesoll@MacBook-Pro-6.local/
Signed-off-by: Florian Westphal <fw@strlen.de>
Link: https://lore.kernel.org/r/20230421170300.24115-8-fw@strlen.de
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/verifier.c b/tools/testing/selftests/bpf/prog_tests/verifier.c
index 7c68d78da9ea..7534f5499d11 100644
--- a/tools/testing/selftests/bpf/prog_tests/verifier.c
+++ b/tools/testing/selftests/bpf/prog_tests/verifier.c
@@ -29,6 +29,8 @@
 #include "verifier_map_ret_val.skel.h"
 #include "verifier_masking.skel.h"
 #include "verifier_meta_access.skel.h"
+#include "verifier_netfilter_ctx.skel.h"
+#include "verifier_netfilter_retcode.skel.h"
 #include "verifier_raw_stack.skel.h"
 #include "verifier_raw_tp_writable.skel.h"
 #include "verifier_reg_equal.skel.h"
@@ -103,6 +105,8 @@ void test_verifier_map_ptr(void)              { RUN(verifier_map_ptr); }
 void test_verifier_map_ret_val(void)          { RUN(verifier_map_ret_val); }
 void test_verifier_masking(void)              { RUN(verifier_masking); }
 void test_verifier_meta_access(void)          { RUN(verifier_meta_access); }
+void test_verifier_netfilter_ctx(void)        { RUN(verifier_netfilter_ctx); }
+void test_verifier_netfilter_retcode(void)    { RUN(verifier_netfilter_retcode); }
 void test_verifier_raw_stack(void)            { RUN(verifier_raw_stack); }
 void test_verifier_raw_tp_writable(void)      { RUN(verifier_raw_tp_writable); }
 void test_verifier_reg_equal(void)            { RUN(verifier_reg_equal); }