Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Mon, 4 Jul 2022 21:07:43 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Alexander Potapenko <glider@google.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Christoph Hellwig <hch@lst.de>,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Ilya Leoshkevich <iii@linux.ibm.com>,
        Ingo Molnar <mingo@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Kees Cook <keescook@chromium.org>,
        Marco Elver <elver@google.com>,
        Mark Rutland <mark.rutland@arm.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Pekka Enberg <penberg@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Vegard Nossum <vegard.nossum@oracle.com>,
        Vlastimil Babka <vbabka@suse.cz>, kasan-dev@googlegroups.com,
        linux-mm@kvack.org, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 44/45] mm: fs: initialize fsdata passed to
 write_begin/write_end interface
Message-ID: <YsNIjwTw41y0Ij0n@casper.infradead.org>
References: <20220701142310.2188015-1-glider@google.com>
 <20220701142310.2188015-45-glider@google.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20220701142310.2188015-45-glider@google.com>
Precedence: bulk

On Fri, Jul 01, 2022 at 04:23:09PM +0200, Alexander Potapenko wrote:
> Functions implementing the a_ops->write_end() interface accept the
> `void *fsdata` parameter that is supposed to be initialized by the
> corresponding a_ops->write_begin() (which accepts `void **fsdata`).
> 
> However not all a_ops->write_begin() implementations initialize `fsdata`
> unconditionally, so it may get passed uninitialized to a_ops->write_end(),
> resulting in undefined behavior.

... wait, passing an uninitialised variable to a function *which doesn't
actually use it* is now UB?  What genius came up with that rule?  What
purpose does it serve?