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
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 @@
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) <<