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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-435699982aasm11193342f8f.42.2026.01.17.04.06.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 17 Jan 2026 04:06:37 -0800 (PST) Date: Sat, 17 Jan 2026 12:06:32 +0000 From: David Laight To: Greg KH Cc: Weigang He , mathias.nyman@intel.com, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] usb: xhci: fix missing null termination after copy_from_user() Message-ID: <20260117120632.75e3c394@pumpkin> In-Reply-To: <2026011725-ecosystem-proved-a6ba@gregkh> References: <20260117094631.504232-1-geoffreyhe2@gmail.com> <2026011725-ecosystem-proved-a6ba@gregkh> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sat, 17 Jan 2026 10:58:41 +0100 Greg KH wrote: > On Sat, Jan 17, 2026 at 09:46:31AM +0000, Weigang He wrote: > > The buffer 'buf' is filled by copy_from_user() but is not properly > > null-terminated before being used with strncmp(). If userspace provides > > fewer than 10 bytes, strncmp() may read beyond the copied data into > > uninitialized stack memory. > > But that's fine, it will not match the check, and so it will stop when > told, so no overflow happens anywhere. That's not entirely true. If the user passes "complianc" (without a '\0') and the on-stack buf[9] happens to be 'e' then the test will succeed rather than fail. But the only thing that will get upset is KASAN. More 'interestingly': - why is it min_t() not min(), everything is size_t. - why sizeof(buf) - 1, reading into the last byte won't matter. - why buf[32] not buf[10], even [16] would be plenty for 'future expansion'. David