[PATCH 5.10 11/36] bpf: Refactor and streamline bounds check into helper

Greg Kroah-Hartman
2021-04-26T07:49:43Z

From: Daniel Borkmann <daniel@iogearbox.net>

[ Upstream commit 073815b756c51ba9d8384d924c5d1c03ca3d1ae4 ]

Move the bounds check in adjust_ptr_min_max_vals() into a small helper named
sanitize_check_bounds() in order to simplify the former a bit.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/bpf/verifier.c | 49 +++++++++++++++++++++++++++++--------------
1 file changed, 33 insertions(+), 16 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 94923c2bdd81..1b97fd364ce2 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5883,6 +5883,37 @@ static int check_stack_access_for_ptr_arithmetic(
return 0;
}

+static int sanitize_check_bounds(struct bpf_verifier_env *env,
+ const struct bpf_insn *insn,
+ const struct bpf_reg_state *dst_reg)
+{
+ u32 dst = insn->dst_reg;
+
+ /* For unprivileged we require that resulting offset must be in bounds
+ * in order to be able to sanitize access later on.
+ */
+ if (env->bypass_spec_v1)
+ return 0;
+
+ switch (dst_reg->type) {
+ case PTR_TO_STACK:
+ if (check_stack_access_for_ptr_arithmetic(env, dst, dst_reg,
+ dst_reg->off + dst_reg->var_off.value))
+ return -EACCES;
+ break;
+ case PTR_TO_MAP_VALUE:
+ if (check_map_access(env, dst, dst_reg->off, 1, false)) {
+ verbose(env, "R%d pointer arithmetic of map value goes out of range, "
+ "prohibited for !root\n", dst);
+ return -EACCES;
+ }
+ break;
+ default:
+ break;
+ }
+
+ return 0;
+}

/* Handles arithmetic on a pointer and a scalar: computes new min/max and var_off.
* Caller should also handle BPF_MOV case separately.
@@ -6108,22 +6139,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
__reg_deduce_bounds(dst_reg);
__reg_bound_offset(dst_reg);

- /* For unprivileged we require that resulting offset must be in bounds
- * in order to be able to sanitize access later on.
- */
- if (!env->bypass_spec_v1) {
- if (dst_reg->type == PTR_TO_MAP_VALUE &&
- check_map_access(env, dst, dst_reg->off, 1, false)) {
- verbose(env, "R%d pointer arithmetic of map value goes out of range, "
- "prohibited for !root\n", dst);
- return -EACCES;
- } else if (dst_reg->type == PTR_TO_STACK &&
- check_stack_access_for_ptr_arithmetic(
- env, dst, dst_reg, dst_reg->off +
- dst_reg->var_off.value)) {
- return -EACCES;
- }
- }
+ if (sanitize_check_bounds(env, insn, dst_reg) < 0)
+ return -EACCES;

return 0;
}
--
2.30.2