Commit 24c109bb authored by Daniel Borkmann's avatar Daniel Borkmann
Browse files

bpf: Ensure off_reg has no mixed signed bounds for all types 



The mixed signed bounds check really belongs into retrieve_ptr_limit()
instead of outside of it in adjust_ptr_min_max_vals(). The reason is
that this check is not tied to PTR_TO_MAP_VALUE only, but to all pointer
types that we handle in retrieve_ptr_limit() and given errors from the latter
propagate back to adjust_ptr_min_max_vals() and lead to rejection of the
program, it's a better place to reside to avoid anything slipping through
for future types. The reason why we must reject such off_reg is that we
otherwise would not be able to derive a mask, see details in 9d7eceed
("bpf: restrict unknown scalars of mixed signed bounds for unprivileged").

Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 6f55b2f2

kernel/bpf/verifier.c

+9 −10
Original line number Diff line number Diff line
@@ -5857,12 +5857,18 @@ static struct bpf_insn_aux_data *cur_aux(struct bpf_verifier_env *env) 
}



static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg,

			      u32 *ptr_limit, u8 opcode, bool off_is_neg)

			      const struct bpf_reg_state *off_reg,

			      u32 *ptr_limit, u8 opcode)

{

	bool off_is_neg = off_reg->smin_value < 0;

	bool mask_to_left = (opcode == BPF_ADD &&  off_is_neg) ||

			    (opcode == BPF_SUB && !off_is_neg);

	u32 off, max;



	if (!tnum_is_const(off_reg->var_off) &&

	    (off_reg->smin_value < 0) != (off_reg->smax_value < 0))

		return -EACCES;



	switch (ptr_reg->type) {

	case PTR_TO_STACK:

		/* Offset 0 is out-of-bounds, but acceptable start for the
@@ -5956,7 +5962,7 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, 
	alu_state |= ptr_is_dst_reg ?

		     BPF_ALU_SANITIZE_SRC : BPF_ALU_SANITIZE_DST;



	err = retrieve_ptr_limit(ptr_reg, &alu_limit, opcode, off_is_neg);

	err = retrieve_ptr_limit(ptr_reg, off_reg, &alu_limit, opcode);

	if (err < 0)

		return err;
@@ -6036,8 +6042,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, 
	    smin_ptr = ptr_reg->smin_value, smax_ptr = ptr_reg->smax_value;

	u64 umin_val = off_reg->umin_value, umax_val = off_reg->umax_value,

	    umin_ptr = ptr_reg->umin_value, umax_ptr = ptr_reg->umax_value;

	u32 dst = insn->dst_reg, src = insn->src_reg;

	u8 opcode = BPF_OP(insn->code);

	u32 dst = insn->dst_reg;

	int ret;



	dst_reg = &regs[dst];
@@ -6085,13 +6091,6 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, 
		verbose(env, "R%d pointer arithmetic on %s prohibited\n",

			dst, reg_type_str[ptr_reg->type]);

		return -EACCES;

	case PTR_TO_MAP_VALUE:

		if (!env->env->bypass_spec_v1 && !known && (smin_val < 0) != (smax_val < 0)) {

			verbose(env, "R%d has unknown scalar with mixed signed bounds, pointer arithmetic with it prohibited for !root\n",

				off_reg == dst_reg ? dst : src);

			return -EACCES;

		}

		fallthrough;

	default:

		break;

	}