From: Pu Lehui 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, we can skip updating stats when stats is NULL. Fixes: 4c46091ee985 ("bpf: Fix KASAN use-after-free Read in compute_effective_progs") Signed-off-by: Pu Lehui --- v4: - roll back to the skip solution, but skip only updating stats. v3: - add static for the per-cpu variable. v2: - Use static per-cpu variables to initialize the stats of dummy_bpf_prog.prog suggested by Eduard. include/linux/filter.h | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/include/linux/filter.h b/include/linux/filter.h index 973233b82dc1..569de3b14279 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -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; - 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); + 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); } -- 2.34.1