From 88c652df02ccf9e7644c012f8375fec24d848be3 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Mon, 5 Oct 2026 08:56:57 -0700 Subject: seq_buf: Add seq_buf_terminate() 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 Acked-by: Alexei Starovoitov Link: https://patch.msgid.link/20261005155708.1471260-7-kees@kernel.org Signed-off-by: Kees Cook --- lib/tests/seq_buf_kunit.c | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) (limited to 'lib/tests') diff --git a/lib/tests/seq_buf_kunit.c b/lib/tests/seq_buf_kunit.c index c6d941a4502f..33d351d0be64 100644 --- a/lib/tests/seq_buf_kunit.c +++ b/lib/tests/seq_buf_kunit.c @@ -632,6 +632,41 @@ 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; + + /* + * seq_buf_putmem() writes no NUL, so only seq_buf_terminate() can + * end these strings early. The NUL in the last byte of buf keeps + * the comparisons in bounds if it does not. + */ + + /* Terminates directly after the data when there is room. */ + memset(buf, 'z', sizeof(buf) - 1); + buf[sizeof(buf) - 1] = '\0'; + seq_buf_init(&s, buf, sizeof(buf)); + seq_buf_putmem(&s, "ab", 2); + 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) - 1); + buf[sizeof(buf) - 1] = '\0'; + seq_buf_init(&s, buf, 4); + seq_buf_putmem(&s, "abcdef", 6); + 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), @@ -655,6 +690,7 @@ 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), {} }; -- cgit v1.2.3