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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" <tytso@mit.edu>
Cc: stable@kernel.org
This commit is contained in:
Theodore Ts'o 2009-11-23 07:24:46 -05:00
parent 2de770a406
commit 503358ae01
1 changed files with 4 additions and 4 deletions
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8
fs/ext4/super.c
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@ -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) <<