Merge branch 'bpf-invalidate-rcu-pointers-after-final-spin-unlock'

Ning Ding says:

====================
bpf: Invalidate RCU pointers after final spin unlock

In a sleepable BPF program, a spin lock can provide the only RCU protection
for a kptr. The final spin unlock ends that protection, but the verifier
leaves the pointer valid. Another CPU can then free the object before the
pointer is used. A capability-limited runtime PoC triggered a
KASAN-confirmed task_struct use-after-free.

Patch 1 invalidates RCU-protected pointers only when an unlock leaves the
final RCU-protected context. Patch 2 adds a negative sleepable test and
positive controls for non-sleepable and explicit-RCU contexts.

Testing used fresh QEMU/KVM guests with KASAN enabled. The patched focused
test passed all three expected outcomes. The full task_kfunc test passed
all 39 subtests, and the selected RCU, refcount, and spin-lock group had no
failures.
---
v2:
  - Rebase onto bpf-next commit 60781269e2.
  - Target bpf-next and split the fix from its selftests, as requested.
  - Add positive controls for RCU contexts that remain valid after unlock.

v1: https://lore.kernel.org/r/20260802231248.2781334-1-dingning04@gmail.com
====================

Link: https://patch.msgid.link/20260803112615.3362122-1-dingning04@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

kernel/bpf/verifier.c

@@ -206,6 +206,7 @@ static int acquire_reference(struct bpf_verifier_env *env, int insn_idx, int par
 static int release_reference_nomark(struct bpf_verifier_state *state, int id);
 static int release_reference(struct bpf_verifier_env *env, int id);
 static void invalidate_non_owning_refs(struct bpf_verifier_env *env);
+static void invalidate_rcu_protected_refs(struct bpf_verifier_env *env);
 static bool in_rbtree_lock_required_cb(struct bpf_verifier_env *env);
 static bool is_tracing_prog_type(enum bpf_prog_type type);
 static int ref_set_non_owning(struct bpf_verifier_env *env,
@@ -7165,6 +7166,7 @@ static int process_spin_lock(struct bpf_verifier_env *env, struct bpf_reg_state
 			return err;
 		}
 	} else {
+		bool was_in_rcu_cs;
 		void *ptr;
 		int type;
 
@@ -7192,10 +7194,13 @@ static int process_spin_lock(struct bpf_verifier_env *env, struct bpf_reg_state
 			verbose(env, "%s_unlock cannot be out of order\n", lock_str);
 			return -EINVAL;
 		}
+		was_in_rcu_cs = in_rcu_cs(env);
 		if (release_lock_state(cur, type, reg->id, ptr)) {
 			verbose(env, "%s_unlock of different lock\n", lock_str);
 			return -EINVAL;
 		}
+		if (was_in_rcu_cs && !in_rcu_cs(env))
+			invalidate_rcu_protected_refs(env);
 
 		invalidate_non_owning_refs(env);
 	}

tools/testing/selftests/bpf/prog_tests/task_kfunc.c

@@ -176,6 +176,8 @@ static const char * const success_tests[] = {
 	"test_task_from_pid_current",
 	"test_task_from_pid_invalid",
 	"task_kfunc_acquire_trusted_walked",
+	"task_kfunc_acquire_after_spin_unlock_non_sleepable",
+	"task_kfunc_acquire_after_spin_unlock_explicit_rcu",
 	"test_task_kfunc_flavor_relo",
 	"test_task_kfunc_flavor_relo_not_found",
 };

tools/testing/selftests/bpf/progs/task_kfunc_common.h

@@ -20,6 +20,18 @@ struct {
 	__uint(max_entries, 1);
 } __tasks_kfunc_map SEC(".maps");
 
+struct task_kptr_lock_value {
+	struct bpf_spin_lock lock;
+	struct task_struct __kptr * task;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__type(key, int);
+	__type(value, struct task_kptr_lock_value);
+	__uint(max_entries, 1);
+} task_kptr_lock_map SEC(".maps");
+
 struct task_struct *bpf_task_acquire(struct task_struct *p) __ksym;
 void bpf_task_release(struct task_struct *p) __ksym;
 struct task_struct *bpf_task_from_pid(s32 pid) __ksym;

tools/testing/selftests/bpf/progs/task_kfunc_failure.c

@@ -378,3 +378,27 @@ int BPF_PROG(task_kfunc_release_in_map, struct task_struct *task, u64 clone_flag
 
 	return 0;
 }
+
+SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
+__failure __msg("R1 must be a rcu pointer")
+int BPF_PROG(task_kfunc_acquire_after_final_spin_unlock)
+{
+	struct task_kptr_lock_value *v;
+	struct task_struct *task, *acquired;
+	int key = 0;
+
+	v = bpf_map_lookup_elem(&task_kptr_lock_map, &key);
+	if (!v)
+		return 0;
+
+	bpf_spin_lock(&v->lock);
+	task = v->task;
+	bpf_spin_unlock(&v->lock);
+	if (!task)
+		return 0;
+
+	acquired = bpf_task_acquire(task);
+	if (acquired)
+		bpf_task_release(acquired);
+	return 0;
+}

tools/testing/selftests/bpf/progs/task_kfunc_success.c

@@ -6,6 +6,7 @@
 #include <bpf/bpf_helpers.h>
 
 #include "../bpf_experimental.h"
+#include "bpf_misc.h"
 #include "task_kfunc_common.h"
 
 char _license[] SEC("license") = "GPL";
@@ -366,6 +367,53 @@ int BPF_PROG(task_kfunc_acquire_trusted_walked, struct task_struct *task, u64 cl
 	return 0;
 }
 
+SEC("fentry/" SYS_PREFIX "sys_getpgid")
+int BPF_PROG(task_kfunc_acquire_after_spin_unlock_non_sleepable)
+{
+	struct task_kptr_lock_value *v;
+	struct task_struct *task, *acquired;
+	int key = 0;
+
+	v = bpf_map_lookup_elem(&task_kptr_lock_map, &key);
+	if (!v)
+		return 0;
+
+	bpf_spin_lock(&v->lock);
+	task = v->task;
+	bpf_spin_unlock(&v->lock);
+	if (!task)
+		return 0;
+
+	acquired = bpf_task_acquire(task);
+	if (acquired)
+		bpf_task_release(acquired);
+	return 0;
+}
+
+SEC("fentry.s/" SYS_PREFIX "sys_getpgid")
+int BPF_PROG(task_kfunc_acquire_after_spin_unlock_explicit_rcu)
+{
+	struct task_kptr_lock_value *v;
+	struct task_struct *task, *acquired;
+	int key = 0;
+
+	v = bpf_map_lookup_elem(&task_kptr_lock_map, &key);
+	if (!v)
+		return 0;
+
+	bpf_rcu_read_lock();
+	bpf_spin_lock(&v->lock);
+	task = v->task;
+	bpf_spin_unlock(&v->lock);
+	if (task) {
+		acquired = bpf_task_acquire(task);
+		if (acquired)
+			bpf_task_release(acquired);
+	}
+	bpf_rcu_read_unlock();
+	return 0;
+}
+
 SEC("syscall")
 int test_task_from_vpid_current(const void *ctx)
 {