A verifier-tracked spin lock provides implicit RCU protection while held. Consequently, a kptr loaded from a lock-protected map value is marked MEM_RCU. process_spin_lock() invalidates non-owning references on unlock, but leaves RCU-protected references intact. This is correct while another RCU context remains active. However, for a sleepable program, releasing its final lock can end the only RCU-protected context. The verifier then allows a MEM_RCU pointer to be used after its protection has ended. Invalidate RCU-protected references when a successful unlock changes in_rcu_cs() from true to false. Non-sleepable programs remain in their invocation-wide implicit RCU context, and an explicit RCU read-side section continues to protect pointers across the unlock. A task kptr retained across the final unlock can race with removal of the map kptr and bpf_task_release(). This was confirmed to result in a task_struct use-after-free in __bpf_get_task_stack(). Add a negative sleepable regression and positive non-sleepable and explicit RCU controls. Fixes: 5861d1e8dbc4 ("bpf: Allow bpf_spin_{lock,unlock} in sleepable progs") Assisted-by: Codex:gpt-5.6-sol Assisted-by: ChatGPT:GPT-5.6-Pro Signed-off-by: Ning Ding --- kernel/bpf/verifier.c | 5 ++ .../selftests/bpf/prog_tests/task_kfunc.c | 2 + .../selftests/bpf/progs/task_kfunc_common.h | 12 +++++ .../selftests/bpf/progs/task_kfunc_failure.c | 24 ++++++++++ .../selftests/bpf/progs/task_kfunc_success.c | 48 +++++++++++++++++++ 5 files changed, 91 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index fdc5fbb1f78c..aea9fdbbd33a 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -204,6 +204,7 @@ 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, @@ -7051,6 +7052,7 @@ 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; @@ -7078,10 +7080,13 @@ 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); } diff --git a/tools/testing/selftests/bpf/prog_tests/task_kfunc.c b/tools/testing/selftests/bpf/prog_tests/task_kfunc.c index e6e95c1416e6..fbd7855712c1 100644 --- a/tools/testing/selftests/bpf/prog_tests/task_kfunc.c +++ b/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", }; diff --git a/tools/testing/selftests/bpf/progs/task_kfunc_common.h b/tools/testing/selftests/bpf/progs/task_kfunc_common.h index e9c4fea7a4bb..052c9d0e3e2a 100644 --- a/tools/testing/selftests/bpf/progs/task_kfunc_common.h +++ b/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; diff --git a/tools/testing/selftests/bpf/progs/task_kfunc_failure.c b/tools/testing/selftests/bpf/progs/task_kfunc_failure.c index 8942b5478129..7a0c7ee95511 100644 --- a/tools/testing/selftests/bpf/progs/task_kfunc_failure.c +++ b/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; +} diff --git a/tools/testing/selftests/bpf/progs/task_kfunc_success.c b/tools/testing/selftests/bpf/progs/task_kfunc_success.c index d63a79ee33dc..2bab7634c9df 100644 --- a/tools/testing/selftests/bpf/progs/task_kfunc_success.c +++ b/tools/testing/selftests/bpf/progs/task_kfunc_success.c @@ -6,6 +6,7 @@ #include #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) { -- 2.43.0