From 7b7b8b5960102566bd625ae829d1f330c5b5d104 Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Thu, 3 Sep 2026 16:44:23 +0200 Subject: [PATCH] bpf: Reject resilient lock operations in rbtree callbacks __bpf_rbtree_add() keeps parent and link pointers live across calls to the program-supplied comparison callback. The verifier therefore requires the root's lock to remain held throughout the callback. The helper path enforces this rule for bpf_spin_lock() and bpf_spin_unlock(), but the resilient lock kfunc argument path does not. Since resilient locks may protect BPF rbtree roots, a callback can release the root lock and let another CPU remove and free the node referenced by the in-progress tree walk. The walk then resumes using freed pointers. Reject resilient lock kfuncs in an rbtree comparison callback, matching the existing policy for the spin lock helpers. Resilient-lock-protected trees remain valid when their comparison callbacks leave lock state alone. Fixes: 0de2046137f9 ("bpf: Implement verifier support for rqspinlock") Reported-by: Nicholas Carlini Suggested-by: Nicholas Carlini Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20260903144433.1716731-6-memxor@gmail.com Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f540279ff4ab..32d31fa67036 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -13241,6 +13241,11 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_call_arg_me { int flags = PROCESS_RES_LOCK; + if (in_rbtree_lock_required_cb(env)) { + verbose(env, "can't res_spin_{lock,unlock} in rbtree cb\n"); + return -EACCES; + } + if (reg->type != PTR_TO_MAP_VALUE && reg->type != (PTR_TO_BTF_ID | MEM_ALLOC)) { verbose(env, "%s doesn't point to map value or allocated object\n", reg_arg_name(env, argno));