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Tue, 11 Nov 2025 11:24:45 -0800 (PST) Date: Wed, 12 Nov 2025 00:54:41 +0530 From: Ayaan Mirza Baig To: Paul Menzel Cc: marcel@holtmann.org, luiz.dentz@gmail.com, linux-bluetooth@vger.kernel.org Subject: Re: [PATCH] drivers/bluetooth: btbcm: Use kmalloc_array() to prevent overflow Message-ID: References: <20251111142041.229145-1-ayaanmirzabaig85@gmail.com> <78ccae43-731d-4cee-868d-50d3c5842ea8@molgen.mpg.de> Precedence: bulk X-Mailing-List: linux-bluetooth@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <78ccae43-731d-4cee-868d-50d3c5842ea8@molgen.mpg.de> On Tue, Nov 11, 2025 at 04:20:14PM +0100, Paul Menzel wrote: > > Replace the open-coded multiplication in kmalloc() with a call > > to kmalloc_array() to prevent potential integer overflows. > > Excuse my ignorance, how would that overflow happen? How is the generated > code different? Hi Paul, The compiler firstly calculates the size then calles kmalloc(). If BCM_FW_NAME_COUNT_MAX and BCM_FW_NAME_LEN are two large unsigned numbers, their product can le larget than SIZE_T_MAX, this then leads to it wrapping to a modulo of SIZE_T_MAX. kmalloc() then gets called with this tiny, wrapped size. It allocates a small buffer, and the when the code is executed further, believing it has a large buffer, writes past the end of the tiny buffer causing a heap buffer overflow. > I’d add a dot/period at the end of the sentence. Thanks! I'll keep that in mind for the future. Regards, Ayaan Mirza Baig --- P.S. By the way, I'm a second year engineering student and I apologize for any stupid-ish thing I might have done. Also I would love to learn from my mistakes, any tips and pointers are highly appreciated.