[PATCH 5.16 111/164] bpf: Fix crash due to out of bounds access into reg2btf_ids.

Greg Kroah-Hartman
2022-02-28T18:10:04Z

From: Kumar Kartikeya Dwivedi <memxor@gmail.com>

[ Upstream commit 45ce4b4f9009102cd9f581196d480a59208690c1 ]

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.

Fixes: c25b2ae13603 ("bpf: Replace PTR_TO_XXX_OR_NULL with PTR_TO_XXX | PTR_MAYBE_NULL")
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220216201943.624869-1-memxor@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/bpf/btf.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 1621f9d45fbda..c9da250fee38c 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -5676,7 +5676,8 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
}
if (check_ctx_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;
@@ -5694,7 +5695,7 @@ 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,
--
2.34.1