From 8c39925e98d498b9531343066ef82ae39e41adae Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Thu, 28 Apr 2022 16:57:51 -0700 Subject: [PATCH] bpf: Fix crash due to out of bounds access into reg2btf_ids. commit 45ce4b4f9009102cd9f581196d480a59208690c1 upstream When commit e6ac2450d6de ("bpf: Support bpf program calling kernel function") added kfunc support, it defined reg2btf_ids as a cheap way to translate the verifier reg type to the appropriate btf_vmlinux BTF ID, however commit c25b2ae13603 ("bpf: Replace PTR_TO_XXX_OR_NULL with PTR_TO_XXX | PTR_MAYBE_NULL") moved the __BPF_REG_TYPE_MAX from the last member of bpf_reg_type enum to after the base register types, and defined other variants using type flag composition. However, now, the direct usage of reg->type to index into reg2btf_ids may no longer fall into __BPF_REG_TYPE_MAX range, and hence lead to out of bounds access and kernel crash on dereference of bad pointer. [backport note: commit 3363bd0cfbb80 ("bpf: Extend kfunc with PTR_TO_CTX, PTR_TO_MEM argument support") was introduced after 5.15 and contains an out of bound reg2btf_ids access. Since that commit hasn't been backported, this patch doesn't include fix to that access. If we backport that commit in future, we need to fix its faulting access as well.] Fixes: c25b2ae13603 ("bpf: Replace PTR_TO_XXX_OR_NULL with PTR_TO_XXX | PTR_MAYBE_NULL") Signed-off-by: Kumar Kartikeya Dwivedi Signed-off-by: Hao Luo Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/bpf/20220216201943.624869-1-memxor@gmail.com Cc: stable@vger.kernel.org # v5.15+ Signed-off-by: Greg Kroah-Hartman --- kernel/bpf/btf.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index ba471f3..40df350 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -5510,9 +5510,9 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, if (reg->type == PTR_TO_BTF_ID) { reg_btf = reg->btf; reg_ref_id = reg->btf_id; - } else if (reg2btf_ids[reg->type]) { + } else if (reg2btf_ids[base_type(reg->type)]) { reg_btf = btf_vmlinux; - reg_ref_id = *reg2btf_ids[reg->type]; + reg_ref_id = *reg2btf_ids[base_type(reg->type)]; } else { bpf_log(log, "kernel function %s args#%d expected pointer to %s %s but R%d is not a pointer to btf_id\n", func_name, i, -- 2.7.4