From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Subject: Re: [RFC PATCH] poll() in 32-bit applications does not handle timeout of -1 properly on 64-bit kernels Date: Tue, 7 Feb 2012 00:38:19 +0000 Message-ID: <20120207003819.GH23916@ZenIV.linux.org.uk> References: <4F306ACA.4090404@akamai.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" To: Josh Hunt Return-path: Content-Disposition: inline In-Reply-To: <4F306ACA.4090404@akamai.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Mon, Feb 06, 2012 at 06:05:30PM -0600, Josh Hunt wrote: > We've hit an issue where our 32-bit applications, when running on a > 64-bit kernel, using poll() and passing in a value of -1 for the timeout > return after ~49 days (2^32 msec). Instead of waiting indefinitely as it > is stated they should. Reproducing the issue is trivial. I've > instrumented the kernel and found we are hitting the case where poll() > believes we've passed in a positive number and thus creates a timespec, > etc. Currently poll() is defined in userspace as: > > int poll(struct pollfd *ufds, nfds_t nfds, int timeout); > > but in the kernel timeout is of type long. > > I can think of a few ways to solve this. One, which is the patch I've > attached, is to change the type of timeout to int in the kernel. I'm not > certain the ramifications this may have since it's changing a syscall's > arguments which may be a big no-no :) Another way I am proposing is by > bounds checking. Currently we do the following: > > if (timeout_msecs >= 0) { > to = &end_time; > poll_select_set_timeout(to, timeout_msecs / MSEC_PER_SEC, > NSEC_PER_MSEC * (timeout_msecs % MSEC_PER_SEC)); > } > > We could add an upper bound on timeout_msecs to say < 0xffffffff. I'm > not sure if either is acceptable though. Or just add compat_sys_poll() with that argument being int and have it call sys_poll(). The value will be sign-extended...