Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752016AbXKSSWA (ORCPT ); Mon, 19 Nov 2007 13:22:00 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751410AbXKSSVf (ORCPT ); Mon, 19 Nov 2007 13:21:35 -0500 Received: from pentafluge.infradead.org ([213.146.154.40]:41882 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751096AbXKSSVd (ORCPT ); Mon, 19 Nov 2007 13:21:33 -0500 Date: Mon, 19 Nov 2007 10:18:08 -0800 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: Justin Forbes , Zwane Mwaikambo , "Theodore Ts'o" , Randy Dunlap , Dave Jones , Chuck Wolber , Chris Wedgwood , Michael Krufky , Chuck Ebbert , Domenico Andreoli , torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, bunk@kernel.org, "David S. Miller" Subject: [patch 02/26] Fix compat futex hangs. Message-ID: <20071119181808.GC15425@kroah.com> References: <20071119181438.617190424@mini.kroah.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline; filename="fix-compat-futex-hangs.patch" In-Reply-To: <20071119181746.GA15425@kroah.com> User-Agent: Mutt/1.5.16 (2007-06-09) X-Bad-Reply: References and In-Reply-To but no 'Re:' in Subject. Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3551 Lines: 109 From: David Miller 2.6.22-stable review patch. If anyone has any objections, please let us know. ------------------ [FUTEX]: Fix address computation in compat code. [ Upstream commit: 3c5fd9c77d609b51c0bab682c9d40cbb496ec6f1 ] compat_exit_robust_list() computes a pointer to the futex entry in userspace as follows: (void __user *)entry + futex_offset 'entry' is a 'struct robust_list __user *', and 'futex_offset' is a 'compat_long_t' (typically a 's32'). Things explode if the 32-bit sign bit is set in futex_offset. Type promotion sign extends futex_offset to a 64-bit value before adding it to 'entry'. This triggered a problem on sparc64 running 32-bit applications which would lock up a cpu looping forever in the fault handling for the userspace load in handle_futex_death(). Compat userspace runs with address masking (wherein the cpu zeros out the top 32-bits of every effective address given to a memory operation instruction) so the sparc64 fault handler accounts for this by zero'ing out the top 32-bits of the fault address too. Since the kernel properly uses the compat_uptr interfaces, kernel side accesses to compat userspace work too since they will only use addresses with the top 32-bit clear. Because of this compat futex layer bug we get into the following loop when executing the get_user() load near the top of handle_futex_death(): 1) load from address '0xfffffffff7f16bd8', FAULT 2) fault handler clears upper 32-bits, processes fault for address '0xf7f16bd8' which succeeds 3) goto #1 I want to thank Bernd Zeimetz, Josip Rodin, and Fabio Massimo Di Nitto for their tireless efforts helping me track down this bug. Signed-off-by: David S. Miller Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- kernel/futex_compat.c | 24 +++++++++++++++++++----- 1 file changed, 19 insertions(+), 5 deletions(-) --- a/kernel/futex_compat.c +++ b/kernel/futex_compat.c @@ -29,6 +29,15 @@ fetch_robust_entry(compat_uptr_t *uentry return 0; } +static void __user *futex_uaddr(struct robust_list *entry, + compat_long_t futex_offset) +{ + compat_uptr_t base = ptr_to_compat(entry); + void __user *uaddr = compat_ptr(base + futex_offset); + + return uaddr; +} + /* * Walk curr->robust_list (very carefully, it's a userspace list!) * and mark any locks found there dead, and notify any waiters. @@ -61,18 +70,23 @@ void compat_exit_robust_list(struct task if (fetch_robust_entry(&upending, &pending, &head->list_op_pending, &pip)) return; - if (pending) - handle_futex_death((void __user *)pending + futex_offset, curr, pip); + if (pending) { + void __user *uaddr = futex_uaddr(pending, + futex_offset); + handle_futex_death(uaddr, curr, pip); + } while (entry != (struct robust_list __user *) &head->list) { /* * A pending lock might already be on the list, so * dont process it twice: */ - if (entry != pending) - if (handle_futex_death((void __user *)entry + futex_offset, - curr, pi)) + if (entry != pending) { + void __user *uaddr = futex_uaddr(entry, + futex_offset); + if (handle_futex_death(uaddr, curr, pi)) return; + } /* * Fetch the next entry in the list: -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/