selftests/bpf: filter by pid to avoid cross-test interference

The test installs a kprobe on __sys_connect and checks that
bpf_probe_write_user() can modify the syscall argument. However, any
concurrent thread in any other test that calls connect() will also
trigger the kprobe and have its sockaddr silently overwritten, causing
flaky failures in unrelated tests.

Constrain the hook to the current test process by filtering on a PID
stored as a global variable in .bss. Initialize the .bss value from
user space before bpf_object__load() using bpf_map__set_initial_value(),
and validate the bss map value size to catch layout mismatches.

No new map is introduced and the test keeps the existing non-skeleton
flow.

Signed-off-by: Sun Jian <sun.jian.kdev@gmail.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260306083330.518627-1-sun.jian.kdev@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/testing/selftests/bpf/prog_tests/probe_user.c b/tools/testing/selftests/bpf/prog_tests/probe_user.c
index 8721671321de8d0a568a537acf618af8b9647ad8..b3e17a329cb47164b33eed0cccf3cb9b6c1865a4 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/probe_user.c
+++ b/tools/testing/selftests/bpf/prog_tests/probe_user.c
@@ -20,6 +20,11 @@ void serial_test_probe_user(void)
        struct bpf_program *kprobe_progs[prog_count];
        struct bpf_object *obj;
        static const int zero = 0;
+       struct test_pro_bss {
+               struct sockaddr_in old;
+               __u32 test_pid;
+       };
+       struct test_pro_bss results = {};
        size_t i;
 
        obj = bpf_object__open_file(obj_file, &opts);
@@ -34,6 +39,23 @@ void serial_test_probe_user(void)
                        goto cleanup;
        }
 
+       {
+               struct bpf_map *bss_map;
+               struct test_pro_bss bss_init = {};
+
+               bss_init.test_pid = getpid();
+               bss_map = bpf_object__find_map_by_name(obj, "test_pro.bss");
+               if (!ASSERT_OK_PTR(bss_map, "find_bss_map"))
+                       goto cleanup;
+               if (!ASSERT_EQ(bpf_map__value_size(bss_map), sizeof(bss_init),
+                              "bss_size"))
+                       goto cleanup;
+               err = bpf_map__set_initial_value(bss_map, &bss_init,
+                                                sizeof(bss_init));
+               if (!ASSERT_OK(err, "set_bss_init"))
+                       goto cleanup;
+       }
+
        err = bpf_object__load(obj);
        if (CHECK(err, "obj_load", "err %d\n", err))
                goto cleanup;
@@ -62,11 +84,13 @@ void serial_test_probe_user(void)
        connect(sock_fd, &curr, sizeof(curr));
        close(sock_fd);
 
-       err = bpf_map_lookup_elem(results_map_fd, &zero, &tmp);
+       err = bpf_map_lookup_elem(results_map_fd, &zero, &results);
        if (CHECK(err, "get_kprobe_res",
                  "failed to get kprobe res: %d\n", err))
                goto cleanup;
 
+       memcpy(&tmp, &results.old, sizeof(tmp));
+
        in = (struct sockaddr_in *)&tmp;
        if (CHECK(memcmp(&tmp, &orig, sizeof(orig)), "check_kprobe_res",
                  "wrong kprobe res from probe read: %s:%u\n",

diff --git a/tools/testing/selftests/bpf/progs/test_probe_user.c b/tools/testing/selftests/bpf/progs/test_probe_user.c
index a8e501af9604d82b2eb8fc1e5aea0903bd112792..4bc86c7654b14b1a8e5ad13a4dff3354cd3e8d21 100644 (file)
--- a/tools/testing/selftests/bpf/progs/test_probe_user.c
+++ b/tools/testing/selftests/bpf/progs/test_probe_user.c
@@ -5,13 +5,22 @@
 #include <bpf/bpf_core_read.h>
 #include "bpf_misc.h"
 
-static struct sockaddr_in old;
+struct test_pro_bss {
+       struct sockaddr_in old;
+       __u32 test_pid;
+};
+
+struct test_pro_bss bss;
 
 static int handle_sys_connect_common(struct sockaddr_in *uservaddr)
 {
        struct sockaddr_in new;
+       __u32 cur = bpf_get_current_pid_tgid() >> 32;
+
+       if (bss.test_pid && cur != bss.test_pid)
+               return 0;
 
-       bpf_probe_read_user(&old, sizeof(old), uservaddr);
+       bpf_probe_read_user(&bss.old, sizeof(bss.old), uservaddr);
        __builtin_memset(&new, 0xab, sizeof(new));
        bpf_probe_write_user(uservaddr, &new, sizeof(new));