It looks like there is an issue in bpf_tracing_prog_attach, in the "prog->aux->dst_trampoline and tgt_prog is NULL" case. One can construct a sequence of events when prog->aux->attach_btf will be NULL, and bpf_trampoline_compute_key will fail. BUG: kernel NULL pointer dereference, address: 0000000000000058 Call Trace: <TASK> ? __die+0x20/0x70 ? page_fault_oops+0x15b/0x430 ? fixup_exception+0x22/0x330 ? exc_page_fault+0x6f/0x170 ? asm_exc_page_fault+0x22/0x30 ? bpf_tracing_prog_attach+0x279/0x560 ? btf_obj_id+0x5/0x10 bpf_tracing_prog_attach+0x439/0x560 __sys_bpf+0x1cf4/0x2de0 __x64_sys_bpf+0x1c/0x30 do_syscall_64+0x41/0xf0 entry_SYSCALL_64_after_hwframe+0x6e/0x76 The issue seems to be not relevant to the previous changes with recursive tracing prog attach, because the reproducing test doesn't actually include recursive fentry attaching. Signed-off-by: Dmitrii Dolgov <9erthalion6@xxxxxxxxx> --- kernel/bpf/syscall.c | 4 +- .../bpf/prog_tests/recursive_attach.c | 48 +++++++++++++++++++ .../bpf/progs/fentry_recursive_target.c | 11 +++++ 3 files changed, 62 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index a595d7a62dbc..e01a949dfed7 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -3197,7 +3197,9 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog, goto out_unlock; } btf_id = prog->aux->attach_btf_id; - key = bpf_trampoline_compute_key(NULL, prog->aux->attach_btf, btf_id); + if (prog->aux->attach_btf) + key = bpf_trampoline_compute_key(NULL, prog->aux->attach_btf, + btf_id); } if (!prog->aux->dst_trampoline || diff --git a/tools/testing/selftests/bpf/prog_tests/recursive_attach.c b/tools/testing/selftests/bpf/prog_tests/recursive_attach.c index 9c422dd92c4e..a4abf1745e62 100644 --- a/tools/testing/selftests/bpf/prog_tests/recursive_attach.c +++ b/tools/testing/selftests/bpf/prog_tests/recursive_attach.c @@ -83,3 +83,51 @@ void test_recursive_fentry_attach(void) fentry_recursive__destroy(tracing_chain[i]); } } + +/* + * Test that a tracing prog reattachment (when we land in + * "prog->aux->dst_trampoline and tgt_prog is NULL" branch in + * bpf_tracing_prog_attach) does not lead to a crash due to missing attach_btf + */ +void test_fentry_attach_btf_presence(void) +{ + struct fentry_recursive_target *target_skel = NULL; + struct fentry_recursive *tracing_skel = NULL; + struct bpf_program *prog; + int err, link_fd, tgt_prog_fd; + + target_skel = fentry_recursive_target__open_and_load(); + if (!ASSERT_OK_PTR(target_skel, "fentry_recursive_target__open_and_load")) + goto close_prog; + + tracing_skel = fentry_recursive__open(); + if (!ASSERT_OK_PTR(tracing_skel, "fentry_recursive__open")) + goto close_prog; + + prog = tracing_skel->progs.recursive_attach; + tgt_prog_fd = bpf_program__fd(target_skel->progs.fentry_target); + err = bpf_program__set_attach_target(prog, tgt_prog_fd, "fentry_target"); + if (!ASSERT_OK(err, "bpf_program__set_attach_target")) + goto close_prog; + + err = fentry_recursive__load(tracing_skel); + if (!ASSERT_OK(err, "fentry_recursive__load")) + goto close_prog; + + LIBBPF_OPTS(bpf_link_create_opts, link_opts); + + link_fd = bpf_link_create(bpf_program__fd(tracing_skel->progs.recursive_attach), + 0, BPF_TRACE_FENTRY, &link_opts); + if (!ASSERT_GE(link_fd, 0, "link_fd")) + goto close_prog; + + fentry_recursive__detach(tracing_skel); + + err = fentry_recursive__attach(tracing_skel); + if (!ASSERT_ERR(err, "fentry_recursive__attach")) + goto close_prog; + +close_prog: + fentry_recursive_target__destroy(target_skel); + fentry_recursive__destroy(tracing_skel); +} diff --git a/tools/testing/selftests/bpf/progs/fentry_recursive_target.c b/tools/testing/selftests/bpf/progs/fentry_recursive_target.c index b6fb8ebd598d..f812d2de0c3c 100644 --- a/tools/testing/selftests/bpf/progs/fentry_recursive_target.c +++ b/tools/testing/selftests/bpf/progs/fentry_recursive_target.c @@ -18,3 +18,14 @@ int BPF_PROG(test1, int a) test1_result = a == 1; return 0; } + +/* + * Dummy bpf prog for testing attach_btf presence when attaching an fentry + * program. + */ +SEC("raw_tp/sys_enter") +int BPF_PROG(fentry_target, struct pt_regs *regs, long id) +{ + test1_result = id == 1; + return 0; +} -- 2.41.0