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[198.0.35.241]) by smtp.gmail.com with ESMTPSA id a8-20020a170902900800b0019a70a42b0asm168526plp.169.2023.03.02.14.39.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Mar 2023 14:39:18 -0800 (PST) Message-ID: <64012596.170a0220.1940.0a34@mx.google.com> X-Google-Original-Message-ID: <202303021434.@keescook> Date: Thu, 2 Mar 2023 14:39:17 -0800 From: Kees Cook To: Jakub Kicinski Cc: Kees Cook , linux-hardening@vger.kernel.org, bpf@vger.kernel.org Subject: Re: splat in ikheaders_read (bpftrace) References: <20230302112130.6e402a98@kernel.org> <22EA7360-E2FC-4A23-BF0B-EFDE523F9605@kernel.org> <20230302140814.294aece0@kernel.org> <20230302141231.2c0a3761@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230302141231.2c0a3761@kernel.org> Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Thu, Mar 02, 2023 at 02:12:31PM -0800, Jakub Kicinski wrote: > On Thu, 2 Mar 2023 14:08:14 -0800 Jakub Kicinski wrote: > > > static ssize_t > > > ikheaders_read(struct file *file, struct kobject *kobj, > > > struct bin_attribute *bin_attr, > > > char *buf, loff_t off, size_t len) > > > { > > > memcpy(buf, &kernel_headers_data + off, len); > > > return len; > > > } > > > > > > I will take a look at the caller's allocation of "buf" and kernel_headers_data. > > > > Mm. Actually stopping to look at the code - I don't see it bound > > checking against kernel_headers_data_end :| Maybe we need: > > > > @@ -34,6 +35,7 @@ ikheaders_read(struct file *file, struct kobject *kobj, > > struct bin_attribute *bin_attr, > > char *buf, loff_t off, size_t len) > > { > > + len = min_t(size_t, kernel_headers_data_end - kernel_headers_data, len); > > memcpy(buf, &kernel_headers_data + off, len); > > return len; > > } > > Scratch that, the size is set at init time. > My guess was memcpy() thinks the size of kernel_headers_data > is 1 since it's declared as char? I've improved the reporting, and yeah, it's due to the declaration: memcpy: detected buffer overflow: 4096 byte read from buffer of size 1 But that's an easy fix -- this has been done in lots of other places. It needs to be an array, not a single char. (I'm surprised we hadn't seen this before.) diff --git a/kernel/kheaders.c b/kernel/kheaders.c index 8f69772af77b..42163c9e94e5 100644 --- a/kernel/kheaders.c +++ b/kernel/kheaders.c @@ -26,15 +26,15 @@ asm ( " .popsection \n" ); -extern char kernel_headers_data; -extern char kernel_headers_data_end; +extern char kernel_headers_data[]; +extern char kernel_headers_data_end[]; static ssize_t ikheaders_read(struct file *file, struct kobject *kobj, struct bin_attribute *bin_attr, char *buf, loff_t off, size_t len) { - memcpy(buf, &kernel_headers_data + off, len); + memcpy(buf, &kernel_headers_data[off], len); return len; } @@ -48,8 +48,8 @@ static struct bin_attribute kheaders_attr __ro_after_init = { static int __init ikheaders_init(void) { - kheaders_attr.size = (&kernel_headers_data_end - - &kernel_headers_data); + kheaders_attr.size = (kernel_headers_data_end - + kernel_headers_data); return sysfs_create_bin_file(kernel_kobj, &kheaders_attr); } -- Kees Cook