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 7A10D3DA5D9; Thu, 21 May 2026 13:33:28 +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=1779370410; cv=none; b=JofttuYW3Jyt6QN4QfZdTodsvuu2rlTOFmBNxLG10TLvdr0Lu33UKwGm9WqC7qNbva5ZZ0Gnrd9Gh6hYte+7dcFRGl61MY2cKTlw3lpA45rnxIteDoJQRwNLGtgRWhMfqjGpdGFd0Tscll4N9EwXKFpQS+S88rGZhGCaU3ZoN3Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779370410; c=relaxed/simple; bh=T4N6FoAPN5e2cqvWSGS7oEs1xiLk99wdr1LKck0ur78=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=d58JjWDKtFwLOrKo41yGHcEyMHsbUPPe2x+l0iPkN9vrVsG3Y2NlWwB4SySJrHfzgbI1x02TzY+ltg8p3Bqa6/YO1BoMjnAIenPw2pwcjnew/UwAb4UEqGzv7zaRRTIiggn9YdPCz0oHFIy/IdwWjisujVK5oJlXrzJhhwwmh/k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eL7P5sQO; 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="eL7P5sQO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D38751F00A3E; Thu, 21 May 2026 13:33:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779370406; bh=Mj7DVCvMStdFPb34OrcUAAH1hWW4OYzU+C7hp9VpbjY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=eL7P5sQOnRUqovuCINXrhkkCMFQg4gJz9lHl+mo5l/7tWzuLIYX1MykUtmft4cIo2 M+FcdXMoQ4rswOfqo73Od6nx4/NZcLe4hChmGlU7e8EHcktUR9bbKkyMDXjIyfyf9B eV78dkZWgUFtYC1qxRKZKBtpzjNh1YNv+xYbvGb/59goFKFuu3NOIeGjgRpvSgtIPo 8ivmmDGfUlUajD9Xi2Zb0jv40IpLIkZ1zlVqLGUDtdGxm942GdK2191iVOUAdgY/d9 LkEDqWs4BcK2jEMPeiyQHLfliXA1m2lVAX62EVolUfTIC9T8HiuTytz5hngxpheUFV LHEYk2tMnbFvw== From: Kees Cook To: Luis Chamberlain Cc: Kees Cook , Pengpeng Hou , Petr Pavlu , Richard Weinberger , Anton Ivanov , Johannes Berg , "Rafael J. Wysocki" , Len Brown , Corey Minyard , Gabriel Somlo , "Michael S. Tsirkin" , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , David Airlie , Simona Vetter , Bart Van Assche , Jason Gunthorpe , Leon Romanovsky , Laurent Pinchart , Hans de Goede , Mauro Carvalho Chehab , Bjorn Helgaas , Hannes Reinecke , "James E.J. Bottomley" , "Martin K. Petersen" , Daniel Lezcano , Zhang Rui , Lukasz Luba , Greg Kroah-Hartman , Jiri Slaby , Alan Stern , Jason Wang , Xuan Zhuo , =?UTF-8?q?Eugenio=20P=C3=A9rez?= , Jason Baron , Jim Cromie , Tiwei Bie , Benjamin Berg , =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= , "David E. Box" , "Maciej W. Rozycki" , Srinivas Pandruvada , Peter Zijlstra , Heiko Carstens , Vasily Gorbik , Sean Christopherson , Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Vinod Koul , Frank Li , Daniel Gomez , Sami Tolvanen , Aaron Tomlin , Alexander Potapenko , Marco Elver , Dmitry Vyukov , Andrew Morton , John Johansen , Paul Moore , James Morris , "Serge E. Hallyn" , Andy Shevchenko , Georgia Garcia , kvm@vger.kernel.org, dmaengine@vger.kernel.org, linux-modules@vger.kernel.org, kasan-dev@googlegroups.com, linux-mm@kvack.org, apparmor@lists.ubuntu.com, linux-security-module@vger.kernel.org, linux-um@lists.infradead.org, linux-acpi@vger.kernel.org, openipmi-developer@lists.sourceforge.net, qemu-devel@nongnu.org, intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-rdma@vger.kernel.org, linux-media@vger.kernel.org, linux-pci@vger.kernel.org, linux-scsi@vger.kernel.org, linux-pm@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-serial@vger.kernel.org, linux-usb@vger.kernel.org, usb-storage@lists.one-eyed-alien.net, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, netdev@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH 06/11] moduleparam: Add seq_buf-based .get callback alongside .get_str Date: Thu, 21 May 2026 06:33:19 -0700 Message-Id: <20260521133326.2465264-6-kees@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260521133315.work.845-kees@kernel.org> References: <20260521133315.work.845-kees@kernel.org> Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3696; i=kees@kernel.org; h=from:subject; bh=T4N6FoAPN5e2cqvWSGS7oEs1xiLk99wdr1LKck0ur78=; b=owGbwMvMwCVmps19z/KJym7G02pJDFn8nIs2HH8iHuPEcem9X7HM2rJrS2LZVs8vP/M+reLdF K3trxtfdZSyMIhxMciKKbIE2bnHuXi8bQ93n6sIM4eVCWQIAxenAExEwZOR4alreLoXi13roV/i 9/tfrbvsVLZZb2L3Qh33TS8N1v2/U8fwT//2x1KTz9OUg91P7LvT39NrdVL4qeIHRzc9ZcnAHRc /cgAA X-Developer-Key: i=kees@kernel.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: 8bit Add a new struct kernel_param_ops::get callback whose signature takes a struct seq_buf instead of a raw char buffer: int (*get)(struct seq_buf *sb, const struct kernel_param *kp); The previously-legacy .get field is now .get_str (char *buffer); .get is the new seq_buf-aware form. param_attr_show() prefers .get when set, otherwise falls back to .get_str. WARN_ON_ONCE() if both are set. Return contract for .get: < 0 : errno propagated to userspace; seq_buf contents discarded = 0 : success; length derived from seq_buf_used() > 0 : forbidden; the dispatcher WARN_ON_ONCE()s and treats as 0 The default policy on seq_buf_has_overflowed() is silent truncation, matching scnprintf()/sysfs_emit() behaviour. Callbacks that want a specific overflow errno can check seq_buf_has_overflowed() and return their preferred error. No callbacks use .get yet; the legacy path is still the only one in use after this commit. A subsequent commit teaches DEFINE_KERNEL_PARAM_OPS to route initializers by type. Signed-off-by: Kees Cook --- include/linux/moduleparam.h | 13 ++++++++++++- kernel/params.c | 26 ++++++++++++++++++++++++-- 2 files changed, 36 insertions(+), 3 deletions(-) diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h index f5f4148e2504..c52120f6ac28 100644 --- a/include/linux/moduleparam.h +++ b/include/linux/moduleparam.h @@ -7,6 +7,7 @@ #include #include #include +#include #include #include #include @@ -62,7 +63,17 @@ struct kernel_param_ops { unsigned int flags; /* Returns 0, or -errno. arg is in kp->arg. */ int (*set)(const char *val, const struct kernel_param *kp); - /* Returns length written or -errno. Buffer is 4k (ie. be short!) */ + /* + * Format the parameter's value into @s. Return 0 on success + * (length derived from seq_buf_used()) or -errno on error. + * Exactly one of .get and .get_str should be set; the dispatcher + * WARNs and prefers .get if both are. + */ + int (*get)(struct seq_buf *s, const struct kernel_param *kp); + /* + * Returns length written or -errno. Buffer is 4k (ie. be short!). + * Deprecated: callbacks should implement .get instead. + */ int (*get_str)(char *buffer, const struct kernel_param *kp); /* Optional function to free kp->arg when module unloaded. */ void (*free)(void *arg); diff --git a/kernel/params.c b/kernel/params.c index 6852caea1785..4eda2d23ddf2 100644 --- a/kernel/params.c +++ b/kernel/params.c @@ -553,12 +553,34 @@ static ssize_t param_attr_show(const struct module_attribute *mattr, { int count; const struct param_attribute *attribute = to_param_attr(mattr); + const struct kernel_param_ops *ops = attribute->param->ops; - if (!attribute->param->ops->get_str) + if (!ops->get && !ops->get_str) return -EPERM; + WARN_ON_ONCE(ops->get && ops->get_str); + kernel_param_lock(mk->mod); - count = attribute->param->ops->get_str(buf, attribute->param); + if (ops->get) { + struct seq_buf s; + + seq_buf_init(&s, buf, PAGE_SIZE); + count = ops->get(&s, attribute->param); + if (count >= 0) { + WARN_ON_ONCE(count > 0); + count = seq_buf_used(&s); + /* Make sure string is terminated. */ + seq_buf_str(&s); + /* + * If overflowed, reduce count by 1 for trailing + * NUL byte. + */ + if (seq_buf_has_overflowed(&s)) + count--; + } + } else { + count = ops->get_str(buf, attribute->param); + } kernel_param_unlock(mk->mod); return count; } -- 2.34.1