From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f197.google.com (mail-pl1-f197.google.com [209.85.214.197]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DDE944AD4D1 for ; Wed, 16 Sep 2026 22:21:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.197 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789597302; cv=none; b=I9UeaRBR1vsWQjO9dWL3vY/Iv8iPNFC4OBhmxMhIkmhrRUAMnVGbUPUwS9/qkqWWU0X6VU4xC731oNi1E9hOlpllf5LVcoKjJyEVSVo0V6lWLw/JRzdYcZOSjT2nslK+drTYPbSy+KE5amLU6jO+vqTYwIUKLhZgBdDO1fnLqlc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789597302; c=relaxed/simple; bh=3IUthFCIQe0CN7x8Mg7+90SA1ewsCpM6PLVBE4HZS44=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=MbRqkJPCnWrcYtD9cHNjum3U7qsv7gaVwxJXDpSr7XceCDZNz5ND/WeZmI+dMnhuf1b1Lsb+KGNSRh253A9JDbW+6ioFQvICHwa9+RQXpKfEzu+cPQObiiCZMBvUIpp7LL0KBcl7vg+3XPSQPg+MzQzf6+ChKRj5vjOETevfdNo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--morbo.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=eU+xYvOv; arc=none smtp.client-ip=209.85.214.197 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--morbo.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="eU+xYvOv" Received: by mail-pl1-f197.google.com with SMTP id d9443c01a7336-2cfc52ddc55so2613635ad.3 for ; Wed, 16 Sep 2026 15:21:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1789597288; x=1790202088; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=cdC0Aij8DIx1VpvwjMV99CPapZgugvAI9la0yQFpjcc=; b=eU+xYvOveSpQCzax4NbbMciXVi0+Fk5YaOy4U2Z17rt336Gh+ReqdwmK8anC1OSQqh 0YkyT/Vm+AQmCWcQVCplilenIXIPW42+jBxlpXFl5ipawiAtWS/KnChBwvUBoBY7KAqx M0T93a+uqoFrw0s4ZphR7QGoLEkGmd5KhXedwu4o7Lp37VWC+sVf2p6/rxQG8bKfFexy /QH61xnnnxhKSByZ3FaFZTVsrQLd1ew9R69oVkXWZDeNYYgw7eXKDUOiIKpYbnDYReH3 QaYWWju11vyxFN/Y6dOjB4067J5KJJtKWqk3NCMmm2/3XTrnPZbUg346Z9V2t02FUcT9 rH0A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1789597288; x=1790202088; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=cdC0Aij8DIx1VpvwjMV99CPapZgugvAI9la0yQFpjcc=; b=EbKWapLazl058pb2wGVjAQTUCkftii+WewWRqSx0ygLR6Wkea9OimIv79FVWAWJ71X vs/K5UVJbe3vu8ca8EMvTS6+vKGgwZvRsIp/bbbxEGrxbQyRyKtB2hWHvDTDhxdsyUPK uo1zCAixRx31m8C3URD28Ug1AU55jU7+SytQbrQiAsH+BfTy1In1Fwc+Wxv9pVitQwad vu4ebz9YigMs3ft5yBjqdelbsoer+We1Eg9S01N4J6NOYP19fxOYE+zBHRLgax8yEU+n Dq+3qrew5lfRZd40BgT8aW6PVuYK3M2r9kpxiHFbLvmvAi22JeLafyNyUiREHbARQL2B FnoA== X-Forwarded-Encrypted: i=1; AKwUvBwXulMJx5jJzZXfoC+26ZFT7gGWfwGVHQn7lCj1eR+1+gp8PVzknyKp/p7kVte5wdIIdfge9bcDQNLxTvk=@vger.kernel.org X-Gm-Message-State: AFuF++mClEIt7T4rnoWR3+UaGPe3IMR0YZsG72+lr8Od2zCATAyhLi2/ jWhEVUFSlKcbctU+mVxSxrznAjs7uQFKjvCdXGlLt8csK/SbpTSqOB+crVAEdEUWwLjY6dO00Ms W X-Received: from plhy3.prod.google.com ([2002:a17:902:d643:b0:2dd:7e95:7c98]) (user=morbo job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:faf:b0:2dd:8e5:28d with SMTP id d9443c01a7336-2dd8e026e01mr89207705ad.8.1789597287619; Wed, 16 Sep 2026 15:21:27 -0700 (PDT) Date: Wed, 16 Sep 2026 22:21:25 +0000 In-Reply-To: <20260916221528.1256283-1-morbo@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260916221528.1256283-1-morbo@google.com> X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog Message-ID: <20260916222125.1259631-1-morbo@google.com> Subject: [PATCH v2] seq_buf: add seq_buf_strlen(), seq_buf_init_append(), seq_buf_puts_trunc() From: Bill Wendling To: Andrew Morton Cc: Kees Cook , Steven Rostedt , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, Bill Wendling Content-Type: text/plain; charset="UTF-8" Converting some strlcat() call sites seq_buf need behavior seq_buf doesn't currently provide, either directly or without introducing subtle bugs: - seq_buf_strlen(): seq_buf_used() reports the full buffer size when the buffer is completely filled, even though seq_buf_str() then overwrites the final byte with a NUL terminator, leaving only size - 1 bytes of actual content. Callers that need the true length of the NUL-terminated string have to fall back to strlen(seq_buf_str(s)). seq_buf_strlen() mirrors seq_buf_str()'s NUL-termination logic but returns the resulting string's length directly. - seq_buf_init_append(): seq_buf_init() always clears the buffer it's given via seq_buf_clear(). Code migrating from strlcat(buf, ...), which appends to whatever @buf already contains, can't use seq_buf_init() without silently discarding that existing content. seq_buf_init_append() preserves it and positions the seq_buf to append after it. - seq_buf_puts_trunc(): seq_buf_puts() (like seq_buf_printf() and friends) writes nothing at all if the string doesn't fully fit, whereas strlcat() always copies as much of the source as there is room for. Converting a strlcat() call site that relied on that partial-copy behavior to plain seq_buf_puts() can silently drop content that used to survive truncated. seq_buf_puts_trunc() keeps the leading bytes of the string that fit. Assisted-by: LLM Suggested-by: Kees Cook Signed-off-by: Bill Wendling --- v2: Reword the commit message to be clearer and not refer to a series of patches --- include/linux/seq_buf.h | 60 +++++++++++++++++++++++++++++++++++++++++ lib/seq_buf.c | 35 ++++++++++++++++++++++++ 2 files changed, 95 insertions(+) diff --git a/include/linux/seq_buf.h b/include/linux/seq_buf.h index 9f2839e73f8a..a552bcaab07f 100644 --- a/include/linux/seq_buf.h +++ b/include/linux/seq_buf.h @@ -30,6 +30,10 @@ struct seq_buf { .size = SIZE, \ } +/** + * seq_buf_clear - reset the seq_buf to be read / appended from the beginning + * @s: the seq_buf handle + */ static inline void seq_buf_clear(struct seq_buf *s) { s->len = 0; @@ -37,6 +41,14 @@ static inline void seq_buf_clear(struct seq_buf *s) s->buffer[0] = '\0'; } +/** + * seq_buf_init - initialize a seq_buf + * @s: the seq_buf handle + * @buf: pointer to the buffer + * @size: total size of @buf + * + * The contents of the buffer are ignored. + */ static inline void seq_buf_init(struct seq_buf *s, char *buf, unsigned int size) { @@ -45,6 +57,26 @@ 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 clears @buf, 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. @@ -108,6 +140,33 @@ static inline const char *seq_buf_str(struct seq_buf *s) return s->buffer; } +/** + * seq_buf_strlen - get the length of the NUL-terminated string in seq_buf + * @s: the seq_buf handle + * + * Like seq_buf_str(), this makes sure that the buffer in @s is + * NUL-terminated, and returns the length of the resulting string. + * Unlike seq_buf_used(), the returned length is always correct, even + * when the buffer is completely full: in that case seq_buf_used() + * reports @s->size, but the last byte was overwritten with the + * trailing NUL, so only @s->size - 1 bytes of content remain. + * + * Returns: the length of the NUL-terminated string in @s->buffer. + */ +static inline size_t seq_buf_strlen(struct seq_buf *s) +{ + if (WARN_ON(s->size == 0)) + return 0; + + if (seq_buf_buffer_left(s)) { + s->buffer[s->len] = 0; + return s->len; + } + + s->buffer[s->size - 1] = 0; + return s->size - 1; +} + /** * seq_buf_get_buf - get buffer to write arbitrary data to * @s: the seq_buf handle @@ -179,6 +238,7 @@ extern int seq_buf_putmem(struct seq_buf *s, const void *mem, unsigned int len); extern int seq_buf_putmem_hex(struct seq_buf *s, const void *mem, unsigned int len); extern int seq_buf_path(struct seq_buf *s, const struct path *path, const char *esc); +extern size_t seq_buf_puts_trunc(struct seq_buf *s, const char *str); extern int seq_buf_hex_dump(struct seq_buf *s, const char *prefix_str, int prefix_type, int rowsize, int groupsize, const void *buf, size_t len, bool ascii); diff --git a/lib/seq_buf.c b/lib/seq_buf.c index a92093f346da..4d56ac71fafe 100644 --- a/lib/seq_buf.c +++ b/lib/seq_buf.c @@ -376,6 +376,41 @@ int seq_buf_to_user(struct seq_buf *s, char __user *ubuf, size_t start, int cnt) return cnt - ret; } +/** + * seq_buf_puts_trunc - append as much of a string as fits, keeping any of it + * @s: the seq_buf handle + * @str: the string to append + * + * seq_buf_puts() writes nothing at all if @str doesn't fully fit, + * unlike strlcat()/strscpy(), which copy as much of the source as + * there is room for. That all-or-nothing behavior is usually what's + * wanted for building diagnostic/trace text, but it's the wrong + * choice when converting code that relied on strlcat()'s always-copy- + * what-fits truncation to avoid losing content that was already + * appended. This copies the leading bytes of @str that fit, reserving + * room for the NUL terminator later added by seq_buf_str(). + * + * Unlike seq_buf_puts(), this does NOT NUL-terminate @s->buffer as it + * goes (it copies raw bytes via seq_buf_putmem(), not @str's own + * terminator). Callers MUST call seq_buf_str() or seq_buf_strlen() + * before using @s->buffer as a C string. + * + * Returns: the number of bytes copied from @str. + */ +size_t seq_buf_puts_trunc(struct seq_buf *s, const char *str) +{ + size_t left = seq_buf_buffer_left(s); + size_t len; + + if (left <= 1) + return 0; + + len = strnlen(str, left - 1); + seq_buf_putmem(s, str, len); + + return len; +} + /** * seq_buf_hex_dump - print formatted hex dump into the sequence buffer * @s: seq_buf descriptor -- 2.55.0.1082.g2b9226bbc0-goog