From: Theodore Tso Subject: Re: [OOPs] ext4: fixpoint divide exception at ext4_fill_super+0x141c/0x2908 Date: Fri, 6 Nov 2009 14:48:50 -0500 Message-ID: <20091106194850.GE26342@mit.edu> References: <4A93792C.2000705@linux.vnet.ibm.com> <4AF17638.7010105@linux.vnet.ibm.com> <4AF1877C.7010606@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-ext4 , Kamalesh Babulal , sachin p sant , Ramon , aneesh.kumar@in.ibm.com To: Nageswara R Sastry Return-path: Received: from thunk.org ([69.25.196.29]:52086 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759682AbZKFTsr (ORCPT ); Fri, 6 Nov 2009 14:48:47 -0500 Content-Disposition: inline In-Reply-To: <4AF1877C.7010606@linux.vnet.ibm.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed, Nov 04, 2009 at 07:24:04PM +0530, Nageswara R Sastry wrote: > Seems to be I have a little format related issue with the patch. So > resending it. Please accept my apologies. > Sachin thanks for letting me know. > >> > ------------[ cut here ]------------ >> > Kernel BUG at 000003e00429d934 [verbose debug info unavailable] >> > fixpoint divide exception: 0009 [#1] SMP >> >> Please find the patch which solves the following 'fixpoint divide >> exception'. I tested the same and not seeing any KERNEL BUG/exception. Nageswara, Thanks for sending this patch. The problem with it is that it leaves sbi->s_log_groups_per_flex non-zero, but it leaves sbi->s_flex_groups unallocated. This should lead to number of kernel oops caused by a null pointer dereference if there is any attempt to allocate blocks or inodes, or to resize the filesystem. A better fix is would be: ext4: Avoid divide by zero when trying to mount a corrupted file system If s_log_groups_per_flex is greater than 31, then groups_per_flex will will overflow and cause a divide by zero error. This can cause kernel BUG if such a file system is mounted. Thanks to Nageswara R Sastry for analyzing the failure and providing an initial patch. http://bugzilla.kernel.org/show_bug.cgi?id=14287 Signed-off-by: "Theodore Ts'o" diff --git a/fs/ext4/super.c b/fs/ext4/super.c index d4ca92a..8662b2e 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -1673,14 +1673,14 @@ static int ext4_fill_flex_info(struct super_block *sb) size_t size; int i; - if (!sbi->s_es->s_log_groups_per_flex) { + sbi->s_log_groups_per_flex = sbi->s_es->s_log_groups_per_flex; + groups_per_flex = 1 << sbi->s_log_groups_per_flex; + + if (groups_per_flex < 2) { sbi->s_log_groups_per_flex = 0; return 1; } - sbi->s_log_groups_per_flex = sbi->s_es->s_log_groups_per_flex; - groups_per_flex = 1 << sbi->s_log_groups_per_flex;