Commit 45ce4b4f authored by Kumar Kartikeya Dwivedi's avatar Kumar Kartikeya Dwivedi Committed by Alexei Starovoitov
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bpf: Fix crash due to out of bounds access into reg2btf_ids. 



When commit e6ac2450 ("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 c25b2ae1 ("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.

Fixes: c25b2ae1 ("bpf: Replace PTR_TO_XXX_OR_NULL with PTR_TO_XXX | PTR_MAYBE_NULL")
Signed-off-by: default avatarKumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220216201943.624869-1-memxor@gmail.com
parent 61d06f01

kernel/bpf/btf.c

+3 −2
Original line number Diff line number Diff line
@@ -5688,7 +5688,8 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, 
			}

			if (check_ptr_off_reg(env, reg, regno))

				return -EINVAL;

		} else if (is_kfunc && (reg->type == PTR_TO_BTF_ID || reg2btf_ids[reg->type])) {

		} else if (is_kfunc && (reg->type == PTR_TO_BTF_ID ||

			   (reg2btf_ids[base_type(reg->type)] && !type_flag(reg->type)))) {

			const struct btf_type *reg_ref_t;

			const struct btf *reg_btf;

			const char *reg_ref_tname;
@@ -5706,7 +5707,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, 
				reg_ref_id = reg->btf_id;

			} else {

				reg_btf = btf_vmlinux;

				reg_ref_id = *reg2btf_ids[reg->type];

				reg_ref_id = *reg2btf_ids[base_type(reg->type)];

			}



			reg_ref_t = btf_type_skip_modifiers(reg_btf, reg_ref_id,