bpf: Fix invalid prog->stats access when update_effective_progs fails

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix invalid prog->stats access when update_effective_progs fails Syzkaller triggers an invalid memory access issue following fault injection in update_effective_progs. The issue can be described as follows: __cgroup_bpf_detach update_effective_progs compute_effective_progs bpf_prog_array_alloc <-- fault inject purge_effective_progs /* change to dummy_bpf_prog */ array->items[index] = &dummy_bpf_prog.prog ---softirq start--- __do_softirq ... __cgroup_bpf_run_filter_skb __bpf_prog_run_save_cb bpf_prog_run stats = this_cpu_ptr(prog->stats) /* invalid memory access */ flags = u64_stats_update_begin_irqsave(&stats->syncp) ---softirq end--- static_branch_dec(&cgroup_bpf_enabled_key[atype]) The reason is that fault injection caused update_effective_progs to fail and then changed the original prog into dummy_bpf_prog.prog in purge_effective_progs. Then a softirq came, and accessing the members of dummy_bpf_prog.prog in the softirq triggers invalid mem access. To fix it, skip updating stats when stats is NULL.

References

• https://git.kernel.org/stable/c/93d1964773ff513c9bd530f7686d3e48b786fa6b
• https://git.kernel.org/stable/c/bf2c990b012100610c0f1ec5c4ea434da2d080c2
• https://git.kernel.org/stable/c/539137e3038ce6f953efd72110110f03c14c7d97
• https://git.kernel.org/stable/c/56905bb70c8b88421709bb4e32fcba617aa37d41
• https://git.kernel.org/stable/c/2579c356ccd35d06238b176e4b460978186d804b
• https://git.kernel.org/stable/c/7dc211c1159d991db609bdf4b0fb9033c04adcbc