Seven callers call seq_buf_str() only to NUL-terminate the buffer, discarding the returned pointer. Two of them need a comment to say so.
Add seq_buf_terminate(), wrapping the __seq_buf_terminate() helper that seq_buf_str() and seq_buf_strlen() already use, and convert those callers. It returns void: returning the offset would just be seq_buf_strlen() under another name. A zero-sized seq_buf is left untouched, as in the other accessors. Add tests for the three cases: room for the NUL after the data, an overflowed buffer where it lands in the last byte, and a zero-sized buffer that must not be written to. Build tested ARCH=x86_64 defconfig with GCC 16.2.0, plus CONFIG_HIST_TRIGGERS=y and CONFIG_BPF_SYSCALL=y to reach the converted call sites in kernel/trace/trace_events_hist.c and kernel/bpf/diagnostics.c. Tests run 24/24 passing on ARCH=um. Assisted-by: LLM Signed-off-by: Kees Cook <[email protected]> --- include/linux/seq_buf.h | 23 +++++++++++++++++++++++ kernel/bpf/diagnostics.c | 6 +++--- kernel/trace/trace_events.c | 4 ++-- kernel/trace/trace_events_hist.c | 6 ++---- lib/tests/seq_buf_kunit.c | 28 ++++++++++++++++++++++++++++ 5 files changed, 58 insertions(+), 9 deletions(-) diff --git a/include/linux/seq_buf.h b/include/linux/seq_buf.h index 87ccc62f1c62..195e612a212a 100644 --- a/include/linux/seq_buf.h +++ b/include/linux/seq_buf.h @@ -171,6 +171,29 @@ static inline size_t seq_buf_strlen(struct seq_buf *s) return __seq_buf_terminate(s); } +/** + * seq_buf_terminate - NUL-terminate the string in a seq_buf + * @s: the seq_buf handle + * + * Terminate @s->buffer exactly as seq_buf_str() and seq_buf_strlen() do, + * for callers that want neither the pointer nor the length and only need + * the buffer to be safe to read as a C string. A zero-sized seq_buf has + * nowhere to put a NUL and is left untouched. + * + * Nothing is returned on purpose: a caller that wants the length should + * use seq_buf_strlen(), which says so. + * + * After this function is called, s->buffer is safe to use + * in string operations. + */ +static inline void seq_buf_terminate(struct seq_buf *s) +{ + if (s->size == 0) + return; + + __seq_buf_terminate(s); +} + /** * seq_buf_get_buf - get buffer to write arbitrary data to * @s: the seq_buf handle diff --git a/kernel/bpf/diagnostics.c b/kernel/bpf/diagnostics.c index 0abbbe177e31..594cf3c8b74c 100644 --- a/kernel/bpf/diagnostics.c +++ b/kernel/bpf/diagnostics.c @@ -351,7 +351,7 @@ static void diag_fmt_restore(struct bpf_verifier_env *env, struct diag_fmt_mark if (mark.chunk) { mark.chunk->seq.len = mark.len; - seq_buf_str(&mark.chunk->seq); + seq_buf_terminate(&mark.chunk->seq); } } @@ -631,11 +631,11 @@ static void format_disasm_line(struct bpf_verifier_env *env, int insn_idx, return; print_bpf_insn(&cbs, insn, env->allow_ptr_leaks); - seq_buf_str(&ctx.seq); + seq_buf_terminate(&ctx.seq); ctx.seq.len = strnlen(line->text, sizeof(line->text)); while (ctx.seq.len && line->text[ctx.seq.len - 1] == '\n') seq_buf_pop(&ctx.seq); - seq_buf_str(&ctx.seq); + seq_buf_terminate(&ctx.seq); line->valid = true; } diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 9dbc2441763b..39bb391546de 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -4906,7 +4906,7 @@ static __init int event_trace_enable(void) */ __trace_early_add_events(tr); - seq_buf_str(&bootup_event_seq); + seq_buf_terminate(&bootup_event_seq); early_enable_events(tr, bootup_event_buf, false); trace_printk_start_comm(); @@ -4935,7 +4935,7 @@ static __init int event_trace_enable_again(void) if (!tr) return -ENODEV; - seq_buf_str(&bootup_event_seq); + seq_buf_terminate(&bootup_event_seq); early_enable_events(tr, bootup_event_buf, true); return 0; diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index 963e0d6b61fd..57bd1cd5c657 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -2988,8 +2988,7 @@ find_synthetic_field_var(struct hist_trigger_data *target_hist_data, seq_buf_init(&s, synthetic_name, MAX_FILTER_STR_VAL); seq_buf_printf(&s, "synthetic_%s", field_name); - /* Terminate synthetic_name with a NUL. */ - seq_buf_str(&s); + seq_buf_terminate(&s); if (seq_buf_has_overflowed(&s)) { kfree(synthetic_name); @@ -3106,8 +3105,7 @@ create_field_var_hist(struct hist_trigger_data *target_hist_data, if (saved_filter) seq_buf_printf(&s, " if %s", saved_filter); - /* Terminate cmd with a NUL. */ - seq_buf_str(&s); + seq_buf_terminate(&s); if (seq_buf_has_overflowed(&s)) { kfree(cmd); diff --git a/lib/tests/seq_buf_kunit.c b/lib/tests/seq_buf_kunit.c index 569ab3d96f10..b6fc7b784859 100644 --- a/lib/tests/seq_buf_kunit.c +++ b/lib/tests/seq_buf_kunit.c @@ -633,6 +633,33 @@ static void seq_buf_strlen_zero_size_test(struct kunit *test) KUNIT_EXPECT_STREQ(test, buf, "untouched"); } +static void seq_buf_terminate_test(struct kunit *test) +{ + char buf[16]; + struct seq_buf s; + + /* Terminates directly after the data when there is room. */ + memset(buf, 'z', sizeof(buf)); + seq_buf_init(&s, buf, sizeof(buf)); + seq_buf_puts(&s, "ab"); + seq_buf_terminate(&s); + KUNIT_EXPECT_STREQ(test, buf, "ab"); + + /* Terminates in the last byte once the buffer has overflowed. */ + memset(buf, 'z', sizeof(buf)); + seq_buf_init(&s, buf, 4); + seq_buf_puts(&s, "abcdef"); + KUNIT_EXPECT_TRUE(test, seq_buf_has_overflowed(&s)); + seq_buf_terminate(&s); + KUNIT_EXPECT_STREQ(test, buf, "abc"); + + /* A zero-sized seq_buf is left alone. */ + strscpy(buf, "untouched", sizeof(buf)); + seq_buf_init(&s, buf, 0); + seq_buf_terminate(&s); + KUNIT_EXPECT_STREQ(test, buf, "untouched"); +} + static struct kunit_case seq_buf_test_cases[] = { KUNIT_CASE(seq_buf_init_test), KUNIT_CASE(seq_buf_declare_test), @@ -656,6 +683,7 @@ static struct kunit_case seq_buf_test_cases[] = { KUNIT_CASE(seq_buf_strlen_puts_overflow_test), KUNIT_CASE(seq_buf_strlen_embedded_nul_test), KUNIT_CASE(seq_buf_strlen_zero_size_test), + KUNIT_CASE(seq_buf_terminate_test), KUNIT_CASE(seq_buf_do_printk_test), {} }; -- 2.55.0
