From 503358ae01b70ce6909d19dd01287093f6b6271c Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Mon, 23 Nov 2009 07:24:46 -0500 Subject: [PATCH] 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" Cc: stable@kernel.org --- fs/ext4/super.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/fs/ext4/super.c b/fs/ext4/super.c index d4ca92aab514..8662b2e6e9f9 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; - /* We allocate both existing and potentially added groups */ flex_group_count = ((sbi->s_groups_count + groups_per_flex - 1) + ((le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks) + 1) << -- 2.20.1