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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45ef34b834esm33184301f8f.11.2026.06.02.06.04.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Jun 2026 06:04:54 -0700 (PDT) Date: Tue, 2 Jun 2026 14:04:51 +0100 From: David Laight To: Andy Shevchenko Cc: Kees Cook , Luis Chamberlain , Pengpeng Hou , stable@vger.kernel.org, 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 , Eugenio =?UTF-8?B?UMOpcmV6?= , Jason Baron , Jim Cromie , Tiwei Bie , Benjamin Berg , Ilpo =?UTF-8?B?SsOkcnZpbmVu?= , "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" , 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: Re: [PATCH 01/11] params: bound array element output to the caller's page buffer Message-ID: <20260602140451.2e3e6622@pumpkin> In-Reply-To: References: <20260521133315.work.845-kees@kernel.org> <20260521133326.2465264-1-kees@kernel.org> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 2 Jun 2026 14:26:46 +0300 Andy Shevchenko wrote: > On Thu, May 21, 2026 at 06:33:14AM -0700, Kees Cook wrote: > > > > param_array_get() appends each element's string representation into the > > shared sysfs page buffer by passing buffer + off to the element getter. > > > > That works for getters that only write a small bounded string, but > > param_get_charp() and similar helpers format against PAGE_SIZE from the > > pointer they receive. Once off is non-zero, an element getter can > > therefore write past the end of the original sysfs page buffer. > > > > Collect each element into a temporary PAGE_SIZE buffer first and then > > copy only the remaining space into the caller's page buffer. > > ... > > > + elem_buf = kmalloc(PAGE_SIZE, GFP_KERNEL); > > get_free_page() (or how it is called)? The kmalloc() should be faster and I think has to be aligned. There is another patch set to replace get_free_pages() with kmalloc(). Although all these 'show' functions should really head to using a safer interface. Although, at the moment, it is really difficult to find the ones that are guaranteed to be passed a page aligned buffer. -- David > > > + if (!elem_buf) > > + return -ENOMEM; > > + > > for (i = off = 0; i < (arr->num ? *arr->num : arr->max); i++) { > > - /* Replace \n with comma */ > > - if (i) > > - buffer[off - 1] = ','; > > p.arg = arr->elem + arr->elemsize * i; > > check_kparam_locked(p.mod); > > - ret = arr->ops->get(buffer + off, &p); > > + ret = arr->ops->get(elem_buf, &p); > > if (ret < 0) > > - return ret; > > + goto out; > > + ret = min(ret, (int)(PAGE_SIZE - 1 - off)); > > It's usually discouraged to use castings in min/max/clamp. Can we make ret long > or do something different here? > > > + if (!ret) > > + break; > > > + /* Replace the previous element's trailing newline with a comma. */ > > + if (i) > > + buffer[off - 1] = ','; > > Can't we do this after with help of strreplace()? > > > + memcpy(buffer + off, elem_buf, ret); > > off += ret; > > + if (off == PAGE_SIZE - 1) > > + break; > > } > > buffer[off] = '\0'; > > - return off; > > + ret = off; > > +out: > > + kfree(elem_buf); > > + return ret; >