From: Theodore Ts'o Date: Mon, 23 Nov 2009 12:24:46 +0000 (-0500) Subject: ext4: avoid divide by zero when trying to mount a corrupted file system X-Git-Tag: v2.6.31.8~33 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=a7aaaff940e284035a16e07cf90424da386ddce1;p=karo-tx-linux.git ext4: avoid divide by zero when trying to mount a corrupted file system (cherry picked from commit 503358ae01b70ce6909d19dd01287093f6b6271c) 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" Signed-off-by: Greg Kroah-Hartman --- diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 667e672e58c8..bc9e02a3609d 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -1695,14 +1695,14 @@ 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) <<