Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752755AbbBQTCY (ORCPT ); Tue, 17 Feb 2015 14:02:24 -0500 Received: from mout.gmx.net ([212.227.15.18]:54227 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751654AbbBQTCX (ORCPT ); Tue, 17 Feb 2015 14:02:23 -0500 From: Heinrich Schuchardt To: Andrew Morton Cc: "Kirill A. Shutemov" , Peter Zijlstra , Oleg Nesterov , Rik van Riel , Vladimir Davydov , Thomas Gleixner , David Rientjes , Kees Cook , linux-kernel@vger.kernel.org, Guenter Roeck , Heinrich Schuchardt Subject: [PATCH 1/1 v2] kernel/fork.c: avoid division by zero Date: Tue, 17 Feb 2015 20:01:38 +0100 Message-Id: <1424199698-7607-1-git-send-email-xypron.glpk@gmx.de> X-Mailer: git-send-email 2.1.4 X-Provags-ID: V03:K0:wguklldVBzWJgd4vNs2lQFQ3xPiRTYztx5J8h5mvQj0Bu/b9Cmd z858JcljCEcd2RFk/pzEJWmNE0n1CQirIPBYlOfl9mR+8h8AzkFa0aTmj7dT8mWsZFkWTZe cixwQOCW24B1MxI4vPHV7erLwtSBxjFIhE70Oe1rkQA72Gf9N9nlD9tKUS3MIdW/PWjDCDu E6ySRNQuHii+V2YYxL91w== X-UI-Out-Filterresults: notjunk:1; Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1846 Lines: 66 PAGE_SIZE is not guaranteed to be equal to or less than 8 times the THREAD_SIZE. E.g. architecture hexagon may have page size 1M and thread size 4096. This would lead to a division by zero. The futex implementation assumes that tids fit into the FUTEX_TID_MASK. This limits the number of allowable threads. version 2: * use div64_u64 * check against FUTEX_TID_MASK Signed-off-by: Heinrich Schuchardt --- kernel/fork.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/kernel/fork.c b/kernel/fork.c index cf65139..1449923 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -74,6 +74,7 @@ #include #include #include +#include #include #include @@ -255,6 +256,8 @@ void __init __weak arch_task_cache_init(void) { } void __init fork_init(unsigned long mempages) { + u64 temp; + #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR #ifndef ARCH_MIN_TASKALIGN #define ARCH_MIN_TASKALIGN L1_CACHE_BYTES @@ -273,7 +276,16 @@ void __init fork_init(unsigned long mempages) * value: the thread structures can take up at most half * of memory. */ - max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE); + temp = div64_u64((u64) mempages * (u64) PAGE_SIZE, + (u64) THREAD_SIZE * 8UL); + + /* + * The futex code assumes that tids fit into the FUTEX_TID_MASK. + */ + if (temp < FUTEX_TID_MASK) + max_threads = temp; + else + max_threads = FUTEX_TID_MASK; /* * we need to allow at least 20 threads to boot a system -- 2.1.4 -- 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/