From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752224Ab3FZLJL (ORCPT ); Wed, 26 Jun 2013 07:09:11 -0400 Received: from multi.imgtec.com ([194.200.65.239]:37897 "EHLO multi.imgtec.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751166Ab3FZLJI (ORCPT ); Wed, 26 Jun 2013 07:09:08 -0400 Message-ID: <51CACB80.5020706@imgtec.com> Date: Wed, 26 Jun 2013 12:07:44 +0100 From: James Hogan User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130514 Thunderbird/17.0.6 MIME-Version: 1.0 To: Andrew Morton CC: Oleg Nesterov , David Daney , David Daney , LKML , Ralf Baechle , Al Viro , "Kees Cook" , David Daney , "Paul E. McKenney" , David Howells , Dave Jones , , Subject: Re: [PATCH v3] kernel/signal.c: fix BUG_ON with SIG128 (MIPS) References: <1371821962-9151-1-git-send-email-james.hogan@imgtec.com> <51C47864.9030200@gmail.com> <20130621202244.GA16610@redhat.com> <51C4BB86.1020004@caviumnetworks.com> <20130622190940.GA14150@redhat.com> <51C80CF0.4070608@imgtec.com> <20130625144015.1e4e70a0ac888f4ccf5c6a8f@linux-foundation.org> In-Reply-To: X-Enigmail-Version: 1.5.1 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [192.168.154.65] X-SEF-Processed: 7_3_0_01192__2013_06_26_12_08_51 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25/06/13 23:13, James Hogan wrote: > On 25 June 2013 22:40, Andrew Morton wrote: >> Meanwhile, unprivileged users can make a MIPS kernel go BUG. >> >> How much of a problem is this? Obviously less of a problem with MIPS >> than it would be with some other CPU types, but I'd imagine it's still >> awkward in some environments. >> >> If this _is_ considered a problem, can we think of some nasty little >> hack which at least makes the effects less damaging, which we can also >> put into -stable kernels? > > The first rfc patch I sent sort of satisfies that by passing 127 if > sig==128, or slightly better would be passing 126 if sig>=127 (so that > SIFSIGNALED returns true). Effectively #ifdef'ing it on _NSIG>127 as > this patch does may be preferable too. > > That's probably the minimum change necessary to evade the BUG_ON > without removing it. The wait status code will still be wrong, but it > wasn't exactly right before so it's no worse. > > IMO changing the ABI by reducing _NSIG to 127 or 126 isn't appropriate > for stable. How does this look for a nasty/stable fix? >>From 94d734526d61f5c74fd2df1c3ecb677495fc7a23 Mon Sep 17 00:00:00 2001 From: James Hogan Date: Wed, 26 Jun 2013 11:48:11 +0100 Subject: [PATCH 1/1] kernel/signal.c: fix BUG_ON with SIG128 (MIPS) MIPS has 128 signals, the highest of which has the number 128 (they start from 1). The following command causes get_signal_to_deliver() to pass this signal number straight through to do_group_exit() as the exit code: strace sleep 10 & sleep 1 && kill -128 `pidof sleep` However do_group_exit() checks for the core dump bit (0x80) in the exit code which matches in this particular case and the kernel panics: BUG_ON(exit_code & 0x80); /* core dumps don't get here */ As a quick fix, mask out higher bits in the signal number. This effectively matches the exit code from other code paths but avoids the BUG_ON. Signed-off-by: James Hogan Cc: Ralf Baechle Cc: Al Viro Cc: Andrew Morton Cc: Oleg Nesterov Cc: Kees Cook Cc: David Daney Cc: "Paul E. McKenney" Cc: David Howells Cc: Dave Jones Cc: linux-mips@linux-mips.org Cc: stable@vger.kernel.org --- kernel/signal.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/signal.c b/kernel/signal.c index 113411b..9ea8f4f 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2366,8 +2366,14 @@ relock: /* * Death signals, no core dump. + * + * Some architectures (MIPS) have 128 signals which doesn't play + * nicely with the exit code since there are only 7 bits to + * store the terminating signal number. Mask out higher bits to + * avoid overflowing into the core dump bit and triggering + * BUG_ON in do_group_exit. */ - do_group_exit(info->si_signo); + do_group_exit(info->si_signo & 0x7f); /* NOTREACHED */ } spin_unlock_irq(&sighand->siglock); -- 1.8.1.2 From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Wed, 26 Jun 2013 13:09:01 +0200 (CEST) Received: from multi.imgtec.com ([194.200.65.239]:37892 "EHLO multi.imgtec.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S6816900Ab3FZLI7hxAKU (ORCPT ); Wed, 26 Jun 2013 13:08:59 +0200 Message-ID: <51CACB80.5020706@imgtec.com> Date: Wed, 26 Jun 2013 12:07:44 +0100 From: James Hogan User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130514 Thunderbird/17.0.6 MIME-Version: 1.0 To: Andrew Morton CC: Oleg Nesterov , David Daney , David Daney , LKML , Ralf Baechle , Al Viro , "Kees Cook" , David Daney , "Paul E. McKenney" , David Howells , Dave Jones , , Subject: Re: [PATCH v3] kernel/signal.c: fix BUG_ON with SIG128 (MIPS) References: <1371821962-9151-1-git-send-email-james.hogan@imgtec.com> <51C47864.9030200@gmail.com> <20130621202244.GA16610@redhat.com> <51C4BB86.1020004@caviumnetworks.com> <20130622190940.GA14150@redhat.com> <51C80CF0.4070608@imgtec.com> <20130625144015.1e4e70a0ac888f4ccf5c6a8f@linux-foundation.org> In-Reply-To: X-Enigmail-Version: 1.5.1 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [192.168.154.65] X-SEF-Processed: 7_3_0_01192__2013_06_26_12_08_51 Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 37131 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: james.hogan@imgtec.com Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips On 25/06/13 23:13, James Hogan wrote: > On 25 June 2013 22:40, Andrew Morton wrote: >> Meanwhile, unprivileged users can make a MIPS kernel go BUG. >> >> How much of a problem is this? Obviously less of a problem with MIPS >> than it would be with some other CPU types, but I'd imagine it's still >> awkward in some environments. >> >> If this _is_ considered a problem, can we think of some nasty little >> hack which at least makes the effects less damaging, which we can also >> put into -stable kernels? > > The first rfc patch I sent sort of satisfies that by passing 127 if > sig==128, or slightly better would be passing 126 if sig>=127 (so that > SIFSIGNALED returns true). Effectively #ifdef'ing it on _NSIG>127 as > this patch does may be preferable too. > > That's probably the minimum change necessary to evade the BUG_ON > without removing it. The wait status code will still be wrong, but it > wasn't exactly right before so it's no worse. > > IMO changing the ABI by reducing _NSIG to 127 or 126 isn't appropriate > for stable. How does this look for a nasty/stable fix? From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from multi.imgtec.com ([194.200.65.239]:37892 "EHLO multi.imgtec.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S6816900Ab3FZLI7hxAKU (ORCPT ); Wed, 26 Jun 2013 13:08:59 +0200 Message-ID: <51CACB80.5020706@imgtec.com> Date: Wed, 26 Jun 2013 12:07:44 +0100 From: James Hogan MIME-Version: 1.0 Subject: Re: [PATCH v3] kernel/signal.c: fix BUG_ON with SIG128 (MIPS) References: <1371821962-9151-1-git-send-email-james.hogan@imgtec.com> <51C47864.9030200@gmail.com> <20130621202244.GA16610@redhat.com> <51C4BB86.1020004@caviumnetworks.com> <20130622190940.GA14150@redhat.com> <51C80CF0.4070608@imgtec.com> <20130625144015.1e4e70a0ac888f4ccf5c6a8f@linux-foundation.org> In-Reply-To: Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Return-Path: Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-subscribe: List-owner: List-post: List-archive: To: Andrew Morton Cc: Oleg Nesterov , David Daney , David Daney , LKML , Ralf Baechle , Al Viro , Kees Cook , David Daney , "Paul E. McKenney" , David Howells , Dave Jones , linux-mips@linux-mips.org, stable@vger.kernel.org Message-ID: <20130626110744.q5eK40izMzJoc03ME5d5XXHRN7ZhDv3TWBC-0umPdfQ@z> On 25/06/13 23:13, James Hogan wrote: > On 25 June 2013 22:40, Andrew Morton wrote: >> Meanwhile, unprivileged users can make a MIPS kernel go BUG. >> >> How much of a problem is this? Obviously less of a problem with MIPS >> than it would be with some other CPU types, but I'd imagine it's still >> awkward in some environments. >> >> If this _is_ considered a problem, can we think of some nasty little >> hack which at least makes the effects less damaging, which we can also >> put into -stable kernels? > > The first rfc patch I sent sort of satisfies that by passing 127 if > sig==128, or slightly better would be passing 126 if sig>=127 (so that > SIFSIGNALED returns true). Effectively #ifdef'ing it on _NSIG>127 as > this patch does may be preferable too. > > That's probably the minimum change necessary to evade the BUG_ON > without removing it. The wait status code will still be wrong, but it > wasn't exactly right before so it's no worse. > > IMO changing the ABI by reducing _NSIG to 127 or 126 isn't appropriate > for stable. How does this look for a nasty/stable fix?