The verifier could accept an unchecked bpf_refcount_acquire() result for a borrowed RCU-loaded map kptr. If the call returns NULL, passing the result to bpf_obj_drop() can crash the kernel.
Add tests showing that an owned input remains non-NULL, a checked borrowed result is accepted, and an unchecked borrowed result is rejected. Assisted-by: Codex:gpt-5.5 Assisted-by: ChatGPT:GPT-5.6-Thinking Signed-off-by: Ning Ding <[email protected]> --- .../selftests/bpf/progs/refcounted_kptr.c | 61 +++++++++++++++++++ .../bpf/progs/refcounted_kptr_fail.c | 47 ++++++++++++++ 2 files changed, 108 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/refcounted_kptr.c b/tools/testing/selftests/bpf/progs/refcounted_kptr.c index 61906f48025cc..fd35093285c0d 100644 --- a/tools/testing/selftests/bpf/progs/refcounted_kptr.c +++ b/tools/testing/selftests/bpf/progs/refcounted_kptr.c @@ -23,6 +23,15 @@ struct map_value { struct node_data __kptr *node; }; +struct node_refcount_only { + long key; + struct bpf_refcount refcount; +}; + +struct map_value_refcount_only { + struct node_refcount_only __kptr *node; +}; + struct { __uint(type, BPF_MAP_TYPE_ARRAY); __type(key, int); @@ -30,6 +39,13 @@ struct { __uint(max_entries, 2); } stashed_nodes SEC(".maps"); +struct { + __uint(type, BPF_MAP_TYPE_ARRAY); + __type(key, int); + __type(value, struct map_value_refcount_only); + __uint(max_entries, 1); +} stashed_refcount_only SEC(".maps"); + struct node_acquire { long key; long data; @@ -832,6 +848,51 @@ long rbtree_refcounted_node_ref_escapes_owning_input(void *ctx) return 0; } +SEC("tc") +__success +long refcount_acquire_owning_input_no_null_check(void *ctx) +{ + struct node_refcount_only *n, *m; + + n = bpf_obj_new(typeof(*n)); + if (!n) + return 1; + + m = bpf_refcount_acquire(n); + bpf_obj_drop(m); + bpf_obj_drop(n); + + return 0; +} + +SEC("tc") +__success +long refcount_acquire_rcu_map_kptr_null_checked(void *ctx) +{ + struct map_value_refcount_only *mapval; + struct node_refcount_only *n, *m; + int idx = 0; + + mapval = bpf_map_lookup_elem(&stashed_refcount_only, &idx); + if (!mapval) + return 1; + + bpf_rcu_read_lock(); + n = mapval->node; + if (!n) { + bpf_rcu_read_unlock(); + return 2; + } + m = bpf_refcount_acquire(n); + bpf_rcu_read_unlock(); + + if (!m) + return 3; + bpf_obj_drop(m); + + return 0; +} + static long __stash_map_empty_xchg(struct node_data *n, int idx) { struct map_value *mapval = bpf_map_lookup_elem(&stashed_nodes, &idx); diff --git a/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c b/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c index 024ef2aae2008..acd3e81a39168 100644 --- a/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c +++ b/tools/testing/selftests/bpf/progs/refcounted_kptr_fail.c @@ -19,6 +19,15 @@ struct node_refcounted { struct bpf_refcount refcount; }; +struct node_refcount_only { + long key; + struct bpf_refcount refcount; +}; + +struct map_value_refcount_only { + struct node_refcount_only __kptr *node; +}; + extern void bpf_rcu_read_lock(void) __ksym; extern void bpf_rcu_read_unlock(void) __ksym; @@ -28,6 +37,13 @@ private(A) struct bpf_rb_root groot __contains(node_acquire, node); private(B) struct bpf_spin_lock lock; private(B) struct bpf_list_head head __contains(node_refcounted, list); +struct { + __uint(type, BPF_MAP_TYPE_ARRAY); + __type(key, int); + __type(value, struct map_value_refcount_only); + __uint(max_entries, 1); +} stashed_refcount_only SEC(".maps"); + static bool less(struct bpf_rb_node *a, const struct bpf_rb_node *b) { struct node_acquire *node_a; @@ -80,6 +96,37 @@ long refcount_acquire_maybe_null(void *ctx) return 0; } +SEC("?tc") +__failure __msg("Possibly NULL pointer passed to trusted R1") +long refcount_acquire_rcu_map_kptr_unchecked_drop(void *ctx) +{ + struct map_value_refcount_only *mapval; + struct node_refcount_only *tmp, *n, *m; + int idx = 0; + + tmp = bpf_obj_new(typeof(*tmp)); + if (!tmp) + return 3; + bpf_obj_drop(tmp); + + mapval = bpf_map_lookup_elem(&stashed_refcount_only, &idx); + if (!mapval) + return 1; + + bpf_rcu_read_lock(); + n = mapval->node; + if (!n) { + bpf_rcu_read_unlock(); + return 2; + } + m = bpf_refcount_acquire(n); + bpf_rcu_read_unlock(); + + bpf_obj_drop(m); + + return 0; +} + SEC("?tc") __failure __msg("Unreleased reference id=3 alloc_insn={{[0-9]+}}") long rbtree_refcounted_node_ref_escapes_owning_input(void *ctx) -- 2.43.0
