The sk_run_filter function in net/core/filter.c in the Linux kernel
before 2.6.36.2 does not check whether a certain memory location has
been initialized before executing a (1) BPF_S_LD_MEM or (2)
BPF_S_LDX_MEM instruction, which allows local users to obtain
potentially sensitive information from kernel stack memory via a
crafted socket filter.