Use-after-free / memory safety in tracepoint BPF link deallocation (SRCU vs RCU)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 05b34a6355b035..35b1e25bd10437 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1854,6 +1854,10 @@ struct bpf_link_ops { * target hook is sleepable, we'll go through tasks trace RCU GP and * then "classic" RCU GP; this need for chaining tasks trace and * classic RCU GPs is designated by setting bpf_link->sleepable flag + * + * For non-sleepable tracepoint links we go through SRCU gp instead, + * since RCU is not used in that case. Sleepable tracepoints still + * follow the scheme above. */ void (*dealloc_deferred)(struct bpf_link *link); int (*detach)(struct bpf_link *link); diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h index 22ca1c8b54f32b..1d7f29f5e90147 100644 --- a/include/linux/tracepoint.h +++ b/include/linux/tracepoint.h @@ -122,6 +122,22 @@ static inline bool tracepoint_is_faultable(struct tracepoint *tp) { return tp->ext && tp->ext->faultable; } +/* + * Run RCU callback with the appropriate grace period wait for non-faultable + * tracepoints, e.g., those used in atomic context. + */ +static inline void call_tracepoint_unregister_atomic(struct rcu_head *rcu, rcu_callback_t func) +{ + call_srcu(&tracepoint_srcu, rcu, func); +} +/* + * Run RCU callback with the appropriate grace period wait for faultable + * tracepoints, e.g., those used in syscall context. + */ +static inline void call_tracepoint_unregister_syscall(struct rcu_head *rcu, rcu_callback_t func) +{ + call_rcu_tasks_trace(rcu, func); +} #else static inline void tracepoint_synchronize_unregister(void) { } @@ -129,6 +145,10 @@ static inline bool tracepoint_is_faultable(struct tracepoint *tp) { return false; } +static inline void call_tracepoint_unregister_atomic(struct rcu_head *rcu, rcu_callback_t func) +{ } +static inline void call_tracepoint_unregister_syscall(struct rcu_head *rcu, rcu_callback_t func) +{ } #endif #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 274039e36465df..700938782bed2f 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -3261,6 +3261,18 @@ static void bpf_link_defer_dealloc_rcu_gp(struct rcu_head *rcu) bpf_link_dealloc(link); } +static bool bpf_link_is_tracepoint(struct bpf_link *link) +{ + /* + * Only these combinations support a tracepoint bpf_link. + * BPF_LINK_TYPE_TRACING raw_tp progs are hardcoded to use + * bpf_raw_tp_link_lops and thus dealloc_deferred(), see + * bpf_raw_tp_link_attach(). + */ + return link->type == BPF_LINK_TYPE_RAW_TRACEPOINT || + (link->type == BPF_LINK_TYPE_TRACING && link->attach_type == BPF_TRACE_RAW_TP); +} + static void bpf_link_defer_dealloc_mult_rcu_gp(struct rcu_head *rcu) { if (rcu_trace_implies_rcu_gp()) @@ -3279,16 +3291,25 @@ static void bpf_link_free(struct bpf_link *link) if (link->prog) ops->release(link); if (ops->dealloc_deferred) { - /* Schedule BPF link deallocation, which will only then + /* + * Schedule BPF link deallocation, which will only then * trigger putting BPF program refcount. * If underlying BPF program is sleepable or BPF link's target * attach hookpoint is sleepable or otherwise requires RCU GPs * to ensure link and its underlying BPF program is not * reachable anymore, we need to first wait for RCU tasks - * trace sync, and then go through "classic" RCU grace period + * trace sync, and then go through "classic" RCU grace period. + * + * For tracepoint BPF links, we need to go through SRCU grace + * period wait instead when non-faultable tracepoint is used. We + * don't need to chain SRCU grace period waits, however, for the + * faultable case, since it exclusively uses RCU Tasks Trace. */ if (link->sleepable || (link->prog && link->prog->sleepable)) call_rcu_tasks_trace(&link->rcu, bpf_link_defer_dealloc_mult_rcu_gp); + /* We need to do a SRCU grace period wait for non-faultable tracepoint BPF links. */ + else if (bpf_link_is_tracepoint(link)) + call_tracepoint_unregister_atomic(&link->rcu, bpf_link_defer_dealloc_rcu_gp); else call_rcu(&link->rcu, bpf_link_defer_dealloc_rcu_gp); } else if (ops->dealloc) {