The d_path selftest closes its descriptors with close_range() so that its fentry program on filp_close() runs. Commit 056069eb2b66 ("fs: make close_range() synchronous") switched close_range() to filp_close_sync(), so the program still attaches but is never called: test_d_path_basic:FAIL:close trampoline for filp_close was not called With that series, close(), close_range() and the closes on exec and exit all go through filp_close_sync(). Few paths still reach filp_close(), dup2() being one of them, so a program on filp_close() no longer sees most file closes. Allow bpf_d_path() from filp_close_sync(), but only from fentry. filp_close_sync() drops the last file reference inline, so by the time an fexit program runs, file->f_path may already be freed, with no RCU delay for NORCU dentries such as pipes and sockets. Attach the selftest program to filp_close_sync() and keep triggering it with close_range(). Add a test rejecting bpf_d_path() from fexit/filp_close_sync. Assisted-by: LLM Fixes: 056069eb2b66 ("fs: make close_range() synchronous") Signed-off-by: Ihor Solodrai --- v2->v3: * Drop the unreachable BPF_TRACE_FENTRY_MULTI check (Sashiko) * Add a Fixes: tag v2: https://lore.kernel.org/bpf/20260925210347.1364191-1-ihor.solodrai@linux.dev/ v1->v2: * Allow bpf_d_path() from filp_close_sync() only for fentry (bpf-ci-bot) * Add a verifier test rejecting bpf_d_path() from fexit/filp_close_sync v1: https://lore.kernel.org/bpf/20260924204226.190315-1-ihor.solodrai@linux.dev/ The issue was found by BPF CI when running on linux-next: https://github.com/kernel-patches/bpf/actions/runs/35923662147/job/107398237366 --- kernel/trace/bpf_trace.c | 15 +++++++++++-- .../testing/selftests/bpf/prog_tests/d_path.c | 7 ++++--- .../testing/selftests/bpf/progs/test_d_path.c | 2 +- .../selftests/bpf/progs/verifier_d_path.c | 21 +++++++++++++++++++ 4 files changed, 39 insertions(+), 6 deletions(-) diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 29260951aa87..4b2f944bf67f 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -974,6 +974,10 @@ BTF_ID(func, vfs_getattr) BTF_ID(func, filp_close) BTF_SET_END(btf_allowlist_d_path) +BTF_SET_START(btf_allowlist_d_path_fentry) +BTF_ID(func, filp_close_sync) +BTF_SET_END(btf_allowlist_d_path_fentry) + static bool bpf_d_path_allowed(const struct bpf_prog *prog) { if (prog->type == BPF_PROG_TYPE_TRACING && @@ -983,8 +987,15 @@ static bool bpf_d_path_allowed(const struct bpf_prog *prog) if (prog->type == BPF_PROG_TYPE_LSM) return bpf_lsm_is_sleepable_hook(prog->aux->attach_btf_id); - return btf_id_set_contains(&btf_allowlist_d_path, - prog->aux->attach_btf_id); + if (btf_id_set_contains(&btf_allowlist_d_path, + prog->aux->attach_btf_id)) + return true; + + if (btf_id_set_contains(&btf_allowlist_d_path_fentry, + prog->aux->attach_btf_id)) + return prog->expected_attach_type == BPF_TRACE_FENTRY; + + return false; } BTF_ID_LIST_SINGLE(bpf_d_path_btf_ids, struct, path) diff --git a/tools/testing/selftests/bpf/prog_tests/d_path.c b/tools/testing/selftests/bpf/prog_tests/d_path.c index 1a2a2f1abf03..7665e1d28a64 100644 --- a/tools/testing/selftests/bpf/prog_tests/d_path.c +++ b/tools/testing/selftests/bpf/prog_tests/d_path.c @@ -109,8 +109,9 @@ static int trigger_fstat_events(pid_t pid) fstat(indicatorfd, &fileStat); out_close: - /* sys_close no longer triggers filp_close, but we can - * call sys_close_range instead which still does + /* + * filp_close_sync() may be inlined into close(2), so use + * close_range(2), which calls it directly. */ syscall_close(pipefd[0]); syscall_close(pipefd[1]); @@ -165,7 +166,7 @@ static void test_d_path_basic(void) if (CHECK(!bss->called_close, "close", - "trampoline for filp_close was not called\n")) + "trampoline for filp_close_sync was not called\n")) goto cleanup; for (int i = 0; i < MAX_FILES; i++) { diff --git a/tools/testing/selftests/bpf/progs/test_d_path.c b/tools/testing/selftests/bpf/progs/test_d_path.c index 561b2f861808..edb5494a47f7 100644 --- a/tools/testing/selftests/bpf/progs/test_d_path.c +++ b/tools/testing/selftests/bpf/progs/test_d_path.c @@ -41,7 +41,7 @@ int BPF_PROG(prog_stat, struct path *path, struct kstat *stat, return 0; } -SEC("fentry/filp_close") +SEC("fentry/filp_close_sync") int BPF_PROG(prog_close, struct file *file, void *id) { pid_t pid = bpf_get_current_pid_tgid() >> 32; diff --git a/tools/testing/selftests/bpf/progs/verifier_d_path.c b/tools/testing/selftests/bpf/progs/verifier_d_path.c index 87e51a215558..7ab9b6b1d589 100644 --- a/tools/testing/selftests/bpf/progs/verifier_d_path.c +++ b/tools/testing/selftests/bpf/progs/verifier_d_path.c @@ -45,4 +45,25 @@ __naked void d_path_reject(void) : __clobber_all); } +SEC("fexit/filp_close_sync") +__description("d_path fexit reject") +__failure __msg("helper call is not allowed in probe") +__naked void d_path_fexit_reject(void) +{ + asm volatile (" \ + r1 = *(u64 *)(r1 + 0); \ + r2 = r10; \ + r2 += -8; \ + r6 = 0; \ + *(u64*)(r2 + 0) = r6; \ + r3 = 8 ll; \ + call %[bpf_d_path]; \ + r0 = 0; \ + exit; \ + " + : + : __imm(bpf_d_path) + : __clobber_all); +} + char _license[] SEC("license") = "GPL"; base-commit: a804c5742bff224d4cb4d25dd383554d598be32b -- 2.56.0