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

Pu Lehui · gregkh · commit 539137e3038c · 2025-12-18T13:55:00.000+01:00
[ Upstream commit 7dc211c ] 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: 492ecee ("bpf: enable program stats") Signed-off-by: Pu Lehui <pulehui@huawei.com> Link: https://lore.kernel.org/r/20251115102343.2200727-1-pulehui@huaweicloud.com Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
diff --git a/include/linux/filter.h b/include/linux/filter.h
@@ -692,11 +692,13 @@ 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);
 	}
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
@@ -2281,6 +2281,9 @@ 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);
