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bpf: Reject resilient lock operations in rbtree callbacks

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__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: 0de2046137 ("bpf: Implement verifier support for rqspinlock")
Reported-by: Nicholas Carlini <npc@anthropic.com>
Suggested-by: Nicholas Carlini <npc@anthropic.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260903144433.1716731-6-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Kumar Kartikeya Dwivedi 2026-09-03 16:44:23 +02:00 committed by Alexei Starovoitov
parent d9ae3e4c7f
commit 7b7b8b5960
1 changed files with 5 additions and 0 deletions
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5
kernel/bpf/verifier.c
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@ -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));