From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7621D2ED141; Sat, 19 Sep 2026 00:27:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789777641; cv=none; b=sp3MfNAlT92nfID3NNf2eb8gpSxifUrXT7TC+AivVFaYwv5s9z5a+RSLUZTjEQHgxZSUkklQkKe3fThKoMvieZ3GdfyqqHYCNt39M6rjbwcC300vXD2Z2gCC2hGzrZdy+uRR3SvtwOfmHO3IP34fj9yxp3rX9BuUlmWPlIYeDkU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789777641; c=relaxed/simple; bh=g3n4Mc6ZCOTrZ0oyKstJy14X2L3I+LTBsJnqtfZJ9xs=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=pAlRTe959s9f7S9tH4Qsgem3Jtb/YL7M5LXqx78kCh7kG58ClTNuUQrG446cKstX0Rx9L7fjGAOLVfj8ubUrhNF5m7xwEeVAI4RgqoyiRmH01XzFDcD3qFQBJnZGwQXR7Bs1ZZsCL9CIr6ZBCbKCo8+EExNIYRiRiQlTHFXI52w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nrmdqRlE; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="nrmdqRlE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CE7111F008A0; Sat, 19 Sep 2026 00:27:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789777634; bh=HeGhXR3Juett99sfkepIICZY00QfUwUjyLbhtWPzTaM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=nrmdqRlEQRF90lLwBBlxvCiMXyX1NuTFPv0T55a7Y2oEk+v4XR/cXJbgLeONNKt1Y kJy9DCQkO1RQub2k7hH1wn4snnWDi9zAQ4P9dxlSUq/0LWJdk9MGFJsH0vNN9V3Lob OerK9RdT7F6c0wChVuvQSGXd9tyRkwNAMSXDMewKB5aTXy1KFNec9o8hKTz2Dyklsi zJ3pNpwJ9EHbDUnPGeaU+T2gk4C08uY25vSqBlro7mvSZYM7VooDVerS1B72KlvOIW PXBMRRkWnvZFlBPreK24uYD5iJ5uo/HrwbGncEZrEHnKDzxvq9ssOUXPhImWYJFSCo HinxjCSjx7xIw== From: Kees Cook To: Bill Wendling Cc: Kees Cook , "Matthew Wilcox (Oracle)" , Andrew Morton , Andy Shevchenko , David Gow , Petr Mladek , Shuvam Pandey , Steven Rostedt , nikitash.mariiaw@gmail.com, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH v2 6/9] seq_buf: Add seq_buf_init_append() Date: Fri, 18 Sep 2026 17:27:04 -0700 Message-Id: <20260919002714.4060307-6-kees@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260919002658.stay.929-kees@kernel.org> References: <20260919002658.stay.929-kees@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=5159; i=kees@kernel.org; h=from:subject; bh=2jEhoAnmYol0m29D/A4CG+1cEgBdo3afaKT4TBfBk1k=; b=owGbwMvMwCVmps19z/KJym7G02pJDFlrr918q+DlZhubIHxMT+tES5zAkRCXdVOjo24wzJNcN 8X/wGyBjlIWBjEuBlkxRZYgO/c4F4+37eHucxVh5rAygQxh4OIUgIls4WH475RpnrZBLiSMtWaK tfFDrW+JFv+Lpit7eF6Z2739p4m8EsP/GHb7pwENB3/zNTzNusf7/mKDXnTonuLyA3fi5l66zjG bAQA= X-Developer-Key: i=kees@kernel.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: 8bit From: Bill Wendling Several strlcat() call sites being converted to seq_buf need behavior seq_buf doesn't currently provide. The normal seq_buf_init() always sets the new buffer size to 0 via seq_buf_clear(). Code migrating from strlcat(buf, ...), which appends to whatever buf already contains, can't use seq_buf_init() without discarding that existing content. Add seq_buf_init_append(), which preserves the existing contents and positions the seq_buf to append after it. Add KUnit tests for behavior coverage. Tests passed under qemu on ARCH=x86_64 with GCC 16.2.0 and CONFIG_KASAN=y, and on big-endian ARCH=s390 with GCC s390x-linux-gnu 16.1.0. Assisted-by: LLM Signed-off-by: Bill Wendling Co-developed-by: Kees Cook Signed-off-by: Kees Cook --- Cc: "Matthew Wilcox (Oracle)" Cc: Andrew Morton Cc: Andy Shevchenko Cc: David Gow Cc: Petr Mladek Cc: Shuvam Pandey Cc: Steven Rostedt --- include/linux/seq_buf.h | 20 +++++++++++++++ lib/tests/seq_buf_kunit.c | 53 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 73 insertions(+) diff --git a/include/linux/seq_buf.h b/include/linux/seq_buf.h index 7f025c7a68be..89d847d40626 100644 --- a/include/linux/seq_buf.h +++ b/include/linux/seq_buf.h @@ -46,6 +46,26 @@ seq_buf_init(struct seq_buf *s, char *buf, unsigned int size) seq_buf_clear(s); } +/** + * seq_buf_init_append - initialize a seq_buf over a buffer that may + * already hold NUL-terminated content + * @s: the seq_buf handle + * @buf: pointer to the (possibly non-empty) buffer + * @size: total size of @buf + * + * Unlike seq_buf_init(), which always starts @buf at len=0, this + * preserves whatever NUL-terminated content @buf already holds and + * positions @s to append after it. Useful for converting code that used + * to append to an existing buffer with strlcat()/scnprintf() and friends. + */ +static inline void +seq_buf_init_append(struct seq_buf *s, char *buf, unsigned int size) +{ + s->buffer = buf; + s->size = size; + s->len = strnlen(buf, size); +} + /* * seq_buf have a buffer that might overflow. When this happens * len is set to be greater than size. diff --git a/lib/tests/seq_buf_kunit.c b/lib/tests/seq_buf_kunit.c index 0259c8506b89..f3058771d96c 100644 --- a/lib/tests/seq_buf_kunit.c +++ b/lib/tests/seq_buf_kunit.c @@ -29,6 +29,58 @@ static void seq_buf_init_test(struct kunit *test) KUNIT_EXPECT_EQ(test, seq_buf_strlen(&s), 0); } +static void seq_buf_init_append_test(struct kunit *test) +{ + char buf[32] = "hello"; + struct seq_buf s; + + /* Initial string contents match. */ + seq_buf_init_append(&s, buf, sizeof(buf)); + KUNIT_EXPECT_EQ(test, s.size, 32); + KUNIT_EXPECT_EQ(test, s.len, 5); + KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s)); + KUNIT_EXPECT_EQ(test, seq_buf_buffer_left(&s), 32 - 5); + KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 5); + KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "hello"); + KUNIT_EXPECT_EQ(test, seq_buf_strlen(&s), 5); + + /* Appending with space works. */ + seq_buf_puts(&s, " world"); + KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s)); + KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 11); + KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "hello world"); + KUNIT_EXPECT_EQ(test, seq_buf_strlen(&s), 11); + + /* No truncation when space for NUL is present. */ + seq_buf_init_append(&s, buf, 12); + KUNIT_EXPECT_EQ(test, s.size, 12); + KUNIT_EXPECT_EQ(test, s.len, 11); + KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s)); + KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 11); + KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "hello world"); + KUNIT_EXPECT_EQ(test, seq_buf_strlen(&s), 11); + + /* Check for required truncation when full. */ + seq_buf_init_append(&s, buf, 11); + KUNIT_EXPECT_EQ(test, s.size, 11); + KUNIT_EXPECT_EQ(test, s.len, 11); + KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s)); + KUNIT_EXPECT_EQ(test, seq_buf_buffer_left(&s), 0); + KUNIT_EXPECT_EQ(test, seq_buf_used(&s), 11); + KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "hello worl"); + KUNIT_EXPECT_EQ(test, seq_buf_strlen(&s), 10); + + /* + * The size bounds the scan: the string reaches past it, so an + * unbounded strlen() would report 10 here and leave @s overflowed. + */ + seq_buf_init_append(&s, buf, 5); + KUNIT_EXPECT_EQ(test, s.size, 5); + KUNIT_EXPECT_EQ(test, s.len, 5); + KUNIT_EXPECT_FALSE(test, seq_buf_has_overflowed(&s)); + KUNIT_EXPECT_EQ(test, seq_buf_buffer_left(&s), 0); + KUNIT_EXPECT_STREQ(test, seq_buf_str(&s), "hell"); +} static void seq_buf_declare_test(struct kunit *test) { @@ -621,6 +673,7 @@ static void seq_buf_strlen_embedded_nul_test(struct kunit *test) static struct kunit_case seq_buf_test_cases[] = { KUNIT_CASE(seq_buf_init_test), + KUNIT_CASE(seq_buf_init_append_test), KUNIT_CASE(seq_buf_declare_test), KUNIT_CASE(seq_buf_clear_test), KUNIT_CASE(seq_buf_puts_test), -- 2.34.1