From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm2-f12.google.com (mail-wm2-f12.google.com [74.125.225.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 002354AFE14 for ; Wed, 16 Sep 2026 09:50:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.225.140 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789552252; cv=none; b=Ot1xFxWb9M36nLnaP5H1LSg6v8xpb4PBW8Haofy/CZ5EYML1zd1wSjD33X9zn3iaQJK5aXAOHj8qyUE+Ri3c+WXOjU+0/LrxQryr5jZBoqaV0YNgrUuOuB0qi4budJ4bM8LMszEuEW8k9cjHNtOZPFRBaIt6ofYu8T2M22sJ+Wk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789552252; c=relaxed/simple; bh=zVftL0e6KTn1Fup/RmgkkUqXURXldH56P13A6WLi8KQ=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=pxZqbYxpJcrje8P3T/rvJx7tavZlDwlnJdxliR0M7Q997APJcc5WijBb1+KWVM9wlE2uOg4/F89dJYfYQX8FrgO2zMZSr+YfjZ8e4cEyGIdW5E4yyRLhRbZA6SPUYCXLGiJsQX7KPDDyZysvUVqVkh9zR8BQqqxakGbBMxS7+6A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=Dzby88uf; arc=none smtp.client-ip=74.125.225.140 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Dzby88uf" Received: by mail-wm2-f12.google.com with SMTP id 5b1f17b1804b1-49ccead2aecso3137605e9.0 for ; Wed, 16 Sep 2026 02:50:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1789552219; x=1790157019; darn=vger.kernel.org; h=content-transfer-encoding:content-type:mime-version:references :in-reply-to:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=79YAdtaHEv3S3nDvYc6X9C5ar06F3FncZEtUncQdJQ4=; b=Dzby88ufsV19pEuHSQnO0Z3r75FgiJ44qF/jXgKTm3w+wAYVSGDUH6LyexeTQiqa/g mb7EWvB3UuhKI7YAj+i2TOZr9/Z0Jn4HnQ3SO6kUkIrvAwSnRTzKzvfGb0So06LetuEf Ts3VEs9CM5zHiWBu1V4JZ71jpXN6ZkETnLDwqKE7PV3aA5kY0+ABvWOim6YHWnbq5cCK nHzOneSJDYvvXY/C7BkTDDo/hN/r3+9IBjrwRhsKYcoz9kdWM+uOTg6K8qjcDaH6D7EX KA0rYEGGzwyipB5cM3imDGmhTpbUuWgcSiyW3ZIBr1TR7/Q7dN5mD7jr++kuJyreI5UR skeQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1789552219; x=1790157019; h=content-transfer-encoding:content-type:mime-version:references :in-reply-to:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=79YAdtaHEv3S3nDvYc6X9C5ar06F3FncZEtUncQdJQ4=; b=L96nmjjg4kCUYsqiFFaOqcIS+uCixhWXzlB6EkhlP2TavitL/wMell0iBN8IBZxhRj pZ/OiF/7wLKqfyQsdgAytFFeJ4LA4/V2fG7SbQevfbZUVtIBXhO8zMTgnKu3l90mKjj9 tNZ9Gbj4VJGGo5afWv+JibGDAXfyegW9VobawIinyY7FOuQjHwEmQn4IfF8pOmTJxSCr Rew9yZf/Y/laFkEWGmGiO9qXBL+8LGcjNftA7AELvF9mgntDTjfuemp+oa/TcIxkn+3/ UcBRdfN2tyw93xg8KZP8cPzZ9qnGRuAI9+iP8l1WZDCzYwI3qgPJ6sMZetAXchNvC1Lm y41Q== X-Forwarded-Encrypted: i=1; AKwUvByWAfuB/4KlGbHjKYbhzf2f3Liwo5HB3/jC3+XbJcx88MgowOCFrOyqwRbtokvNZO8tVJL5zdjaDRd0@vger.kernel.org X-Gm-Message-State: AFuF++mgFgzuBRosRr/eHyYZ4giamspdlhaHxgIkKT9dhGsvSjaJ6K8D hxMec5W3h086cTqCy7HPg1UN7CXjA6z82tlbdfH2pWUwxuB8HtFC2pNu X-Gm-Gg: AYBFou0CD5E9lKfwMSQT6jwz/jPeC01Gks8ZhbvPdWFHlPG3Nfr3391RvAEoOYRUXij ibgBAUNxAgG1X/mglZYtduc0DBU8wdkyZfC033CWvYw1Gg1GyyTO+mSr62PvoA09wiHPdpKfUXa 6llfqCXkngtZM7Q4MbcecLcd1PiFnkx0wNr3EimnOLG7WXVaKYjrUzUxbQbCp+bbk5TBTiCgiDl DE6OtI4J3Y7qyMYfe8e9PcJReVsakXj24LVjC4fc8Pb+Rqt69rkBKrP3UyGx3cWYeQ7RE14XGnF Yr5gBYezpm/Q7p4N+J/d8nr5cjRJfT3RtKYAU407URKSaWtzq4lE5CTIndjbZBsAfAejMe05Bt+ xzEdDiI67nbt6zDLbJuK0COtfuTqAxNUN+0uwyvS2tHcDAEcgnm3d3Td4+ulsWs3BpkMxzJsXy0 pvLwU2KscVeISS+3TtbEw3+9Caw0jF9GUDiW8y+XklG7+UwYcrqPHOJLJ+Xdjns0ON5ERrfqTGn lNV4Dwr2ES5Kl5QAeE+o7OZfQU8QbKxcL88lmYv1RAFD1c= X-Received: by 2002:a05:600c:4ec6:b0:49c:fea3:8633 with SMTP id 5b1f17b1804b1-49eb732aec0mr19444455e9.24.1789552219000; Wed, 16 Sep 2026 02:50:19 -0700 (PDT) Received: from pumpkin (82-69-66-36.dsl.in-addr.zen.co.uk. [82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49e83b02245sm84055225e9.10.2026.09.16.02.50.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Sep 2026 02:50:18 -0700 (PDT) Date: Wed, 16 Sep 2026 10:50:17 +0100 From: David Laight To: Linus Torvalds Cc: Jann Horn , Christian Brauner , Alexander Viro , Jan Kara , Ingo Molnar , Peter Zijlstra , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Oleg Nesterov , linux-alpha@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-openrisc@vger.kernel.org, linux-parisc@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-um@lists.infradead.org, Jens Axboe , io-uring@vger.kernel.org, netdev@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-gpio@vger.kernel.org, linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, bpf@vger.kernel.org, David Airlie , virtualization@lists.linux.dev, kvm@vger.kernel.org, kexec@lists.infradead.org, linux-hyperv@vger.kernel.org Subject: Re: [PATCH RFC POC 00/50] file: handle files on syscall exit Message-ID: <20260916105017.13ea5e36@pumpkin> In-Reply-To: References: <20260915-work-fd-reserve-unify-folded-v1-0-4d5217d6b246@kernel.org> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-mips@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 Tue, 15 Sep 2026 12:08:57 -0700 Linus Torvalds wrote: > On Tue, 15 Sept 2026 at 10:52, Jann Horn wrote: > > > > Is this mainly about stuff like "we installed a file descriptor and > > then the following put_user() failed"? Because if so, I think a nicer > > fix would be to have a policy of "if userspace provides unwritable > > memory to a syscall, just keep going and pretend the access worked", > > and maybe have a sysctl that kills the process when this happens to > > emphasize that userspace should not be doing this. > > We've done that before, where we just ignore put_user() errors and the > user gets whatever the user gets. > > It is maybe not optimal, but it's fine. You can find quite a lot of > unchecked put_user() calls with a pattern like > > git grep '^[[:space:]]*put_user(.*);' > > and some of them are in core code - see the two in kernel/fork.c, for example. > > One of them says "if userspace has not set up a proper pointer then > tough luck". The other one doesn't even bother with a comment. I think the code should try to return EFAULT (IIRC that is too hard in one of the exec cases). Otherwise very unexpected things might happen if the memory is just readonly. If you ignore the error and the pointer is invalid the application will get a SIGSEGV and (usually) die. But winding back kernel data because a user copy failed is likely to be problematic/difficult and at best have error path code that isn't really tested. As well as writing fd numbers to userspace, some sockopt code tries to wind back if the write to optlen fails (which has been read earlier). I've forgotten which Unix converted EFAULT to SIGSEGV in the system call exit code - I'm sure one of the ones I've used did. David > > The scheduler has two cases too, although one of them is admittedly > for another error case. > > So yes, saying "if you pass bogus arguments, you get what you get" is > a valid model. It's perhaps not the *preferred* model, but it's not > wrong. > > It *would* be wrong to take code that already has error handling and > remove the error handling, though. > > Linus >