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Thu, 02 May 2024 17:41:25 -0700 (PDT) Received: from www.outflux.net ([198.0.35.241]) by smtp.gmail.com with ESMTPSA id f2-20020a170902ce8200b001ecf865a019sm1958663plg.224.2024.05.02.17.41.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 May 2024 17:41:25 -0700 (PDT) Date: Thu, 2 May 2024 17:41:23 -0700 From: Kees Cook To: Al Viro Cc: Christian Brauner , Jan Kara , linux-fsdevel@vger.kernel.org, Zack Rusin , Broadcom internal kernel review list , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Daniel Vetter , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , Andi Shyti , Lucas De Marchi , Matt Atwood , Matthew Auld , Nirmoy Das , Jonathan Cavitt , Will Deacon , Peter Zijlstra , Boqun Feng , Mark Rutland , Kent Overstreet , Masahiro Yamada , Nathan Chancellor , Nicolas Schier , Andrew Morton , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-kbuild@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH 5/5] fs: Convert struct file::f_count to refcount_long_t Message-ID: <202405021736.574A688@keescook> References: <20240502222252.work.690-kees@kernel.org> <20240502223341.1835070-5-keescook@chromium.org> <20240502224250.GM2118490@ZenIV> <202405021548.040579B1C@keescook> <20240502231228.GN2118490@ZenIV> <202405021620.C8115568@keescook> <20240502234152.GP2118490@ZenIV> <202405021708.267B02842@keescook> <20240503001445.GR2118490@ZenIV> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240503001445.GR2118490@ZenIV> On Fri, May 03, 2024 at 01:14:45AM +0100, Al Viro wrote: > On Thu, May 02, 2024 at 05:10:18PM -0700, Kees Cook wrote: > > > But anyway, there needs to be a general "oops I hit 0"-aware form of > > get_file(), and it seems like it should just be get_file() itself... > > ... which brings back the question of what's the sane damage mitigation > for that. Adding arseloads of never-exercised failure exits is generally > a bad idea - it's asking for bitrot and making the thing harder to review > in future. Linus seems to prefer best-effort error recovery to sprinkling BUG()s around. But if that's really the solution, then how about get_file() switching to to use inc_not_zero and BUG on 0? -- Kees Cook