From 0bf1ff3b8c46b9f03ab61e174f7cda8eb9b669ab Mon Sep 17 00:00:00 2001 From: Pu Lehui Date: Mon, 10 Nov 2025 07:17:14 +0000 Subject: [PATCH] bpf: Fix invalid mem access when update_effective_progs fails in __cgroup_bpf_detach 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 stats of dummy_bpf_prog.prog in the softirq triggers invalid mem access. To fix it, we can use static per-cpu variables to initialize the stats of dummy_bpf_prog.prog. Fixes: 4c46091ee985 ("bpf: Fix KASAN use-after-free Read in compute_effective_progs") Signed-off-by: Pu Lehui --- kernel/bpf/core.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index d595fe512498c..c7c9c78f171a6 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -2536,11 +2536,14 @@ static unsigned int __bpf_prog_ret1(const void *ctx, return 1; } +DEFINE_PER_CPU(struct bpf_prog_stats, __dummy_stats); + static struct bpf_prog_dummy { struct bpf_prog prog; } dummy_bpf_prog = { .prog = { .bpf_func = __bpf_prog_ret1, + .stats = &__dummy_stats, }, };