Re: [PATCH bpf v2 2/2] selftests/bpf: Add tests for sock_ops ctx access with same src/dst register

[sun jian]

On Mon, Apr 6, 2026 at 11:15 AM Jiayuan Chen <jiayuan.chen@xxxxxxxxx> wrote:
>
> Add selftests to verify SOCK_OPS_GET_SK() and SOCK_OPS_GET_FIELD()
> correctly return NULL/zero when dst_reg == src_reg and is_fullsock == 0.
>
> Three subtests are included:
>  - get_sk: ctx->sk with same src/dst register (SOCK_OPS_GET_SK)
>  - get_field: ctx->snd_cwnd with same src/dst register (SOCK_OPS_GET_FIELD)
>  - get_sk_diff_reg: ctx->sk with different src/dst register (baseline)
>
> Each BPF program uses inline asm (__naked) to force specific register
> allocation, reads is_fullsock first, then loads the field using the same
> (or different) register. The test triggers TCP_NEW_SYN_RECV via a TCP
> handshake and checks that the result is NULL/zero when is_fullsock == 0.
>
> Test:
>         ./test_progs -a sock_ops_get_sk -v
>         test_sock_ops_get_sk:PASS:join_cgroup 0 nsec
>         test_sock_ops_get_sk:PASS:skel_open_load 0 nsec
>         run_sock_ops_test:PASS:prog_attach 0 nsec
>         run_sock_ops_test:PASS:start_server 0 nsec
>         run_sock_ops_test:PASS:connect_to_fd 0 nsec
>         test_sock_ops_get_sk:PASS:null_seen 0 nsec
>         test_sock_ops_get_sk:PASS:bug_not_detected 0 nsec
>         #419/1   sock_ops_get_sk/get_sk:OK
>         run_sock_ops_test:PASS:prog_attach 0 nsec
>         run_sock_ops_test:PASS:start_server 0 nsec
>         run_sock_ops_test:PASS:connect_to_fd 0 nsec
>         test_sock_ops_get_sk:PASS:field_null_seen 0 nsec
>         test_sock_ops_get_sk:PASS:field_bug_not_detected 0 nsec
>         #419/2   sock_ops_get_sk/get_field:OK
>         run_sock_ops_test:PASS:prog_attach 0 nsec
>         run_sock_ops_test:PASS:start_server 0 nsec
>         run_sock_ops_test:PASS:connect_to_fd 0 nsec
>         test_sock_ops_get_sk:PASS:diff_reg_null_seen 0 nsec
>         test_sock_ops_get_sk:PASS:diff_reg_bug_not_detected 0 nsec
>         #419/3   sock_ops_get_sk/get_sk_diff_reg:OK
>         #419     sock_ops_get_sk:OK
>         Summary: 1/3 PASSED, 0 SKIPPED, 0 FAILED
>
> Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>
> ---
>  .../bpf/prog_tests/sock_ops_get_sk.c          |  77 ++++++++++++
>  .../selftests/bpf/progs/sock_ops_get_sk.c     | 117 ++++++++++++++++++
>  2 files changed, 194 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/sock_ops_get_sk.c
>  create mode 100644 tools/testing/selftests/bpf/progs/sock_ops_get_sk.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/sock_ops_get_sk.c b/tools/testing/selftests/bpf/prog_tests/sock_ops_get_sk.c
> new file mode 100644
> index 0000000000000..e086f7abb197e
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/sock_ops_get_sk.c
> @@ -0,0 +1,77 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <test_progs.h>
> +#include "cgroup_helpers.h"
> +#include "network_helpers.h"
> +#include "sock_ops_get_sk.skel.h"
> +
> +/* See progs/sock_ops_get_sk.c for the bug description. */
> +static void run_sock_ops_test(struct sock_ops_get_sk *skel, int cgroup_fd,
> +                             int prog_fd)
> +{
> +       int server_fd, client_fd, err;
> +
> +       err = bpf_prog_attach(prog_fd, cgroup_fd, BPF_CGROUP_SOCK_OPS, 0);
> +       if (!ASSERT_OK(err, "prog_attach"))
> +               return;
> +
> +       server_fd = start_server(AF_INET, SOCK_STREAM, NULL, 0, 0);
> +       if (!ASSERT_GE(server_fd, 0, "start_server"))
> +               goto detach;
> +
> +       /* Trigger TCP handshake which causes TCP_NEW_SYN_RECV state where
> +        * is_fullsock == 0 and is_locked_tcp_sock == 0.
> +        */
> +       client_fd = connect_to_fd(server_fd, 0);
> +       if (!ASSERT_GE(client_fd, 0, "connect_to_fd"))
> +               goto close_server;
> +
> +       close(client_fd);
> +
> +close_server:
> +       close(server_fd);
> +detach:
> +       bpf_prog_detach(cgroup_fd, BPF_CGROUP_SOCK_OPS);
> +}
> +
> +void test_sock_ops_get_sk(void)
> +{
> +       struct sock_ops_get_sk *skel;
> +       int cgroup_fd;
> +
> +       cgroup_fd = test__join_cgroup("/sock_ops_get_sk");
> +       if (!ASSERT_GE(cgroup_fd, 0, "join_cgroup"))
> +               return;
> +
> +       skel = sock_ops_get_sk__open_and_load();
> +       if (!ASSERT_OK_PTR(skel, "skel_open_load"))
> +               goto close_cgroup;
> +
> +       /* Test SOCK_OPS_GET_SK with same src/dst register */
> +       if (test__start_subtest("get_sk")) {
> +               run_sock_ops_test(skel, cgroup_fd,
> +                                 bpf_program__fd(skel->progs.sock_ops_get_sk_same_reg));
> +               ASSERT_EQ(skel->bss->null_seen, 1, "null_seen");
> +               ASSERT_EQ(skel->bss->bug_detected, 0, "bug_not_detected");
> +       }
> +
> +       /* Test SOCK_OPS_GET_FIELD with same src/dst register */
> +       if (test__start_subtest("get_field")) {
> +               run_sock_ops_test(skel, cgroup_fd,
> +                                 bpf_program__fd(skel->progs.sock_ops_get_field_same_reg));
> +               ASSERT_EQ(skel->bss->field_null_seen, 1, "field_null_seen");
> +               ASSERT_EQ(skel->bss->field_bug_detected, 0, "field_bug_not_detected");
> +       }
> +
> +       /* Test SOCK_OPS_GET_SK with different src/dst register */
> +       if (test__start_subtest("get_sk_diff_reg")) {
> +               run_sock_ops_test(skel, cgroup_fd,
> +                                 bpf_program__fd(skel->progs.sock_ops_get_sk_diff_reg));
> +               ASSERT_EQ(skel->bss->diff_reg_null_seen, 1, "diff_reg_null_seen");
> +               ASSERT_EQ(skel->bss->diff_reg_bug_detected, 0, "diff_reg_bug_not_detected");
> +       }
> +
> +       sock_ops_get_sk__destroy(skel);
> +close_cgroup:
> +       close(cgroup_fd);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/sock_ops_get_sk.c b/tools/testing/selftests/bpf/progs/sock_ops_get_sk.c
> new file mode 100644
> index 0000000000000..3a0689f8ce7ca
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/sock_ops_get_sk.c
> @@ -0,0 +1,117 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include "bpf_misc.h"
> +
> +/*
> + * Test the SOCK_OPS_GET_SK() and SOCK_OPS_GET_FIELD() macros in
> + * sock_ops_convert_ctx_access() when dst_reg == src_reg.
> + *
> + * When dst_reg == src_reg, the macros borrow a temporary register to load
> + * is_fullsock / is_locked_tcp_sock, because dst_reg holds the ctx pointer
> + * and cannot be clobbered before ctx->sk / ctx->field is read. If
> + * is_fullsock == 0 (e.g., TCP_NEW_SYN_RECV with a request_sock), the macro
> + * must still zero dst_reg so the verifier's PTR_TO_SOCKET_OR_NULL /
> + * SCALAR_VALUE type is correct at runtime. A missing clear leaves a stale
> + * ctx pointer in dst_reg that passes NULL checks (GET_SK) or leaks a kernel
> + * address as a scalar (GET_FIELD).
> + *
> + * When dst_reg != src_reg, dst_reg itself is used to load is_fullsock, so
> + * the JEQ (dst_reg == 0) naturally leaves it zeroed on the !fullsock path.
> + */
> +
> +int bug_detected;
> +int null_seen;
> +
> +SEC("sockops")
> +__naked void sock_ops_get_sk_same_reg(void)
> +{
> +       asm volatile (
> +               "r7 = *(u32 *)(r1 + %[is_fullsock_off]);"
> +               "r1 = *(u64 *)(r1 + %[sk_off]);"
> +               "if r7 != 0 goto 2f;"
> +               "if r1 == 0 goto 1f;"
> +               "r1 = %[bug_detected] ll;"
> +               "r2 = 1;"
> +               "*(u32 *)(r1 + 0) = r2;"
> +               "goto 2f;"
> +       "1:"
> +               "r1 = %[null_seen] ll;"
> +               "r2 = 1;"
> +               "*(u32 *)(r1 + 0) = r2;"
> +       "2:"
> +               "r0 = 1;"
> +               "exit;"
> +               :
> +               : __imm_const(is_fullsock_off, offsetof(struct bpf_sock_ops, is_fullsock)),
> +                 __imm_const(sk_off, offsetof(struct bpf_sock_ops, sk)),
> +                 __imm_addr(bug_detected),
> +                 __imm_addr(null_seen)
> +               : __clobber_all);
> +}
> +
> +/* SOCK_OPS_GET_FIELD: same-register, is_locked_tcp_sock == 0 path. */
> +int field_bug_detected;
> +int field_null_seen;
> +
> +SEC("sockops")
> +__naked void sock_ops_get_field_same_reg(void)
> +{
> +       asm volatile (
> +               "r7 = *(u32 *)(r1 + %[is_fullsock_off]);"
> +               "r1 = *(u32 *)(r1 + %[snd_cwnd_off]);"
> +               "if r7 != 0 goto 2f;"
> +               "if r1 == 0 goto 1f;"
> +               "r1 = %[field_bug_detected] ll;"
> +               "r2 = 1;"
> +               "*(u32 *)(r1 + 0) = r2;"
> +               "goto 2f;"
> +       "1:"
> +               "r1 = %[field_null_seen] ll;"
> +               "r2 = 1;"
> +               "*(u32 *)(r1 + 0) = r2;"
> +       "2:"
> +               "r0 = 1;"
> +               "exit;"
> +               :
> +               : __imm_const(is_fullsock_off, offsetof(struct bpf_sock_ops, is_fullsock)),
> +                 __imm_const(snd_cwnd_off, offsetof(struct bpf_sock_ops, snd_cwnd)),
> +                 __imm_addr(field_bug_detected),
> +                 __imm_addr(field_null_seen)
> +               : __clobber_all);
> +}
> +
> +/* SOCK_OPS_GET_SK: different-register, is_fullsock == 0 path. */
> +int diff_reg_bug_detected;
> +int diff_reg_null_seen;
> +
> +SEC("sockops")
> +__naked void sock_ops_get_sk_diff_reg(void)
> +{
> +       asm volatile (
> +               "r7 = r1;"
> +               "r6 = *(u32 *)(r7 + %[is_fullsock_off]);"
> +               "r2 = *(u64 *)(r7 + %[sk_off]);"
> +               "if r6 != 0 goto 2f;"
> +               "if r2 == 0 goto 1f;"
> +               "r1 = %[diff_reg_bug_detected] ll;"
> +               "r3 = 1;"
> +               "*(u32 *)(r1 + 0) = r3;"
> +               "goto 2f;"
> +       "1:"
> +               "r1 = %[diff_reg_null_seen] ll;"
> +               "r3 = 1;"
> +               "*(u32 *)(r1 + 0) = r3;"
> +       "2:"
> +               "r0 = 1;"
> +               "exit;"
> +               :
> +               : __imm_const(is_fullsock_off, offsetof(struct bpf_sock_ops, is_fullsock)),
> +                 __imm_const(sk_off, offsetof(struct bpf_sock_ops, sk)),
> +                 __imm_addr(diff_reg_bug_detected),
> +                 __imm_addr(diff_reg_null_seen)
> +               : __clobber_all);
> +}
> +
> +char _license[] SEC("license") = "GPL";
> --
> 2.43.0
>
>

Reviewed-by: Sun Jian <sun.jian.kdev@xxxxxxxxx>