In the Linux kernel, the following vulnerability has been resolved: quota: Fix potential NULL pointer dereference Below race may cause NULL pointer dereference P1 P2 dquotfreeinode quotaoff dropdquotref removedquotref dquots = idquot(inode) dquots = idquot(inode) srcureadlock dquots[cnt]) != NULL (1) dquots[type] = NULL (2) spinlock(&dquots[cnt]->dqdqblock) (3) .... If dquotfreeinode(or other routines) checks inode's quota pointers (1) before quota_off sets it to NULL(2) and use it (3) after that, NULL pointer dereference will be triggered. So let's fix it by using a temporary pointer to avoid this issue.