Commit 7dc211c1 authored by Pu Lehui's avatar Pu Lehui Committed by Alexei Starovoitov
Browse files

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.

Fixes: 492ecee8 ("bpf: enable program stats")
Signed-off-by: default avatarPu Lehui <pulehui@huawei.com>
Link: https://lore.kernel.org/r/20251115102343.2200727-1-pulehui@huaweicloud.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 4722981c

include/linux/filter.h

+7 −5
Original line number Diff line number Diff line
@@ -712,11 +712,13 @@ static __always_inline u32 __bpf_prog_run(const struct bpf_prog *prog, 
		ret = dfunc(ctx, prog->insnsi, prog->bpf_func);



		duration = sched_clock() - start;

		if (likely(prog->stats)) {

			stats = this_cpu_ptr(prog->stats);

			flags = u64_stats_update_begin_irqsave(&stats->syncp);

			u64_stats_inc(&stats->cnt);

			u64_stats_add(&stats->nsecs, duration);

			u64_stats_update_end_irqrestore(&stats->syncp, flags);

		}

	} else {

		ret = dfunc(ctx, prog->insnsi, prog->bpf_func);

	}

kernel/bpf/syscall.c

+3 −0
Original line number Diff line number Diff line
@@ -2463,6 +2463,9 @@ void notrace bpf_prog_inc_misses_counter(struct bpf_prog *prog) 
	struct bpf_prog_stats *stats;

	unsigned int flags;



	if (unlikely(!prog->stats))

		return;



	stats = this_cpu_ptr(prog->stats);

	flags = u64_stats_update_begin_irqsave(&stats->syncp);

	u64_stats_inc(&stats->misses);