6.7-stable review patch. If anyone has any objections, please let me know.
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From: Dave Marchevsky davemarchevsky@fb.com
[ Upstream commit 1500a5d9f49cb66906d3ea1c9158df25cc41dd40 ]
Refcounted local kptrs are kptrs to user-defined types with a bpf_refcount field. Recent commits ([0], [1]) modified the lifetime of refcounted local kptrs such that the underlying memory is not reused until RCU grace period has elapsed.
Separately, verification of bpf_refcount_acquire calls currently succeeds for MAYBE_NULL non-owning reference input, which is a problem as bpf_refcount_acquire_impl has no handling for this case.
This patch takes advantage of aforementioned lifetime changes to tag bpf_refcount_acquire_impl kfunc KF_RCU, thereby preventing MAYBE_NULL input to the kfunc. The KF_RCU flag applies to all kfunc params; it's fine for it to apply to the void *meta__ign param as that's populated by the verifier and is tagged __ign regardless.
[0]: commit 7e26cd12ad1c ("bpf: Use bpf_mem_free_rcu when bpf_obj_dropping refcounted nodes") is the actual change to allocation behaivor [1]: commit 0816b8c6bf7f ("bpf: Consider non-owning refs to refcounted nodes RCU protected") modified verifier understanding of refcounted local kptrs to match [0]'s changes
Signed-off-by: Dave Marchevsky davemarchevsky@fb.com Fixes: 7c50b1cb76ac ("bpf: Add bpf_refcount_acquire kfunc") Link: https://lore.kernel.org/r/20231107085639.3016113-2-davemarchevsky@fb.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/helpers.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 56b0c1f678ee..6950f0461634 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -2520,7 +2520,7 @@ BTF_ID_FLAGS(func, bpf_obj_new_impl, KF_ACQUIRE | KF_RET_NULL) BTF_ID_FLAGS(func, bpf_percpu_obj_new_impl, KF_ACQUIRE | KF_RET_NULL) BTF_ID_FLAGS(func, bpf_obj_drop_impl, KF_RELEASE) BTF_ID_FLAGS(func, bpf_percpu_obj_drop_impl, KF_RELEASE) -BTF_ID_FLAGS(func, bpf_refcount_acquire_impl, KF_ACQUIRE | KF_RET_NULL) +BTF_ID_FLAGS(func, bpf_refcount_acquire_impl, KF_ACQUIRE | KF_RET_NULL | KF_RCU) BTF_ID_FLAGS(func, bpf_list_push_front_impl) BTF_ID_FLAGS(func, bpf_list_push_back_impl) BTF_ID_FLAGS(func, bpf_list_pop_front, KF_ACQUIRE | KF_RET_NULL)