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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>
This commit is contained in:
Florian Westphal 2023-04-21 19:03:00 +02:00 committed by Alexei Starovoitov
parent 2b99ef22e0
commit 006c0e44ed
3 changed files with 174 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
tools/testing/selftests/bpf/prog_tests/verifier.c
View File

@ -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); }

121
tools/testing/selftests/bpf/progs/verifier_netfilter_ctx.c Normal file
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@ -0,0 +1,121 @@
// SPDX-License-Identifier: GPL-2.0
#include "vmlinux.h"
#include "bpf_misc.h"
#include <bpf/bpf_endian.h>
#include <bpf/bpf_tracing.h>
#include <bpf/bpf_helpers.h>
SEC("netfilter")
__description("netfilter invalid context access, size too short")
__failure __msg("invalid bpf_context access")
__naked void with_invalid_ctx_access_test1(void)
{
asm volatile (" \
r2 = *(u8*)(r1 + %[__bpf_nf_ctx_state]); \
r0 = 0; \
exit; \
" :
: __imm_const(__bpf_nf_ctx_state, offsetof(struct bpf_nf_ctx, state))
: __clobber_all);
}
SEC("netfilter")
__description("netfilter invalid context access, size too short")
__failure __msg("invalid bpf_context access")
__naked void with_invalid_ctx_access_test2(void)
{
asm volatile (" \
r2 = *(u16*)(r1 + %[__bpf_nf_ctx_skb]); \
r0 = 0; \
exit; \
" :
: __imm_const(__bpf_nf_ctx_skb, offsetof(struct bpf_nf_ctx, skb))
: __clobber_all);
}
SEC("netfilter")
__description("netfilter invalid context access, past end of ctx")
__failure __msg("invalid bpf_context access")
__naked void with_invalid_ctx_access_test3(void)
{
asm volatile (" \
r2 = *(u64*)(r1 + %[__bpf_nf_ctx_size]); \
r0 = 0; \
exit; \
" :
: __imm_const(__bpf_nf_ctx_size, sizeof(struct bpf_nf_ctx))
: __clobber_all);
}
SEC("netfilter")
__description("netfilter invalid context, write")
__failure __msg("invalid bpf_context access")
__naked void with_invalid_ctx_access_test4(void)
{
asm volatile (" \
r2 = r1; \
*(u64*)(r2 + 0) = r1; \
r0 = 1; \
exit; \
" :
: __imm_const(__bpf_nf_ctx_skb, offsetof(struct bpf_nf_ctx, skb))
: __clobber_all);
}
#define NF_DROP 0
#define NF_ACCEPT 1
SEC("netfilter")
__description("netfilter valid context read and invalid write")
__failure __msg("only read is supported")
int with_invalid_ctx_access_test5(struct bpf_nf_ctx *ctx)
{
struct nf_hook_state *state = (void *)ctx->state;
state->sk = NULL;
return NF_ACCEPT;
}
extern int bpf_dynptr_from_skb(struct sk_buff *skb, __u64 flags,
struct bpf_dynptr *ptr__uninit) __ksym;
extern void *bpf_dynptr_slice(const struct bpf_dynptr *ptr, uint32_t offset,
void *buffer, uint32_t buffer__sz) __ksym;
SEC("netfilter")
__description("netfilter test prog with skb and state read access")
__success __failure_unpriv
__retval(0)
int with_valid_ctx_access_test6(struct bpf_nf_ctx *ctx)
{
const struct nf_hook_state *state = ctx->state;
struct sk_buff *skb = ctx->skb;
const struct iphdr *iph;
const struct tcphdr *th;
u8 buffer_iph[20] = {};
u8 buffer_th[40] = {};
struct bpf_dynptr ptr;
uint8_t ihl;
if (skb->len <= 20 || bpf_dynptr_from_skb(skb, 0, &ptr))
return NF_ACCEPT;
iph = bpf_dynptr_slice(&ptr, 0, buffer_iph, sizeof(buffer_iph));
if (!iph)
return NF_ACCEPT;
if (state->pf != 2)
return NF_ACCEPT;
ihl = iph->ihl << 2;
th = bpf_dynptr_slice(&ptr, ihl, buffer_th, sizeof(buffer_th));
if (!th)
return NF_ACCEPT;
return th->dest == bpf_htons(22) ? NF_ACCEPT : NF_DROP;
}
char _license[] SEC("license") = "GPL";

49
tools/testing/selftests/bpf/progs/verifier_netfilter_retcode.c Normal file
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@ -0,0 +1,49 @@
// SPDX-License-Identifier: GPL-2.0
#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include "bpf_misc.h"
SEC("netfilter")
__description("bpf_exit with invalid return code. test1")
__failure __msg("R0 is not a known value")
__naked void with_invalid_return_code_test1(void)
{
asm volatile (" \
r0 = *(u64*)(r1 + 0); \
exit; \
" ::: __clobber_all);
}
SEC("netfilter")
__description("bpf_exit with valid return code. test2")
__success
__naked void with_valid_return_code_test2(void)
{
asm volatile (" \
r0 = 0; \
exit; \
" ::: __clobber_all);
}
SEC("netfilter")
__description("bpf_exit with valid return code. test3")
__success
__naked void with_valid_return_code_test3(void)
{
asm volatile (" \
r0 = 1; \
exit; \
" ::: __clobber_all);
}
SEC("netfilter")
__description("bpf_exit with invalid return code. test4")
__failure __msg("R0 has value (0x2; 0x0)")
__naked void with_invalid_return_code_test4(void)
{
asm volatile (" \
r0 = 2; \
exit; \
" ::: __clobber_all);
}