bpf: Generalize check_ctx_reg for reuse with other types

jira VULN-72
cve CVE-2021-4204
commit-author Daniel Borkmann <[email protected]>
commit be80a1d

Generalize the check_ctx_reg() helper function into a more generic named one
so that it can be reused for other register types as well to check whether
their offset is non-zero. No functional change.

	Signed-off-by: Daniel Borkmann <[email protected]>
	Acked-by: John Fastabend <[email protected]>
	Acked-by: Alexei Starovoitov <[email protected]>
(cherry picked from commit be80a1d)
	Signed-off-by: Brett Mastbergen <[email protected]>

Author: bmastbergen

include/linux/bpf_verifier.h

@@ -487,8 +487,8 @@ bpf_prog_offload_replace_insn(struct bpf_verifier_env *env, u32 off,
 void
 bpf_prog_offload_remove_insns(struct bpf_verifier_env *env, u32 off, u32 cnt);
 
-int check_ctx_reg(struct bpf_verifier_env *env,
-		  const struct bpf_reg_state *reg, int regno);
+int check_ptr_off_reg(struct bpf_verifier_env *env,
+		      const struct bpf_reg_state *reg, int regno);
 int check_mem_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
 		   u32 regno, u32 mem_size);
 

kernel/bpf/btf.c

@@ -5494,7 +5494,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 					i, btf_type_str(t));
 				return -EINVAL;
 			}
-			if (check_ctx_reg(env, reg, regno))
+			if (check_ptr_off_reg(env, reg, regno))
 				return -EINVAL;
 		} else if (is_kfunc && (reg->type == PTR_TO_BTF_ID || reg2btf_ids[reg->type])) {
 			const struct btf_type *reg_ref_t;

kernel/bpf/verifier.c

@@ -3661,24 +3661,25 @@ static int get_callee_stack_depth(struct bpf_verifier_env *env,
 }
 #endif
 
-int check_ctx_reg(struct bpf_verifier_env *env,
-		  const struct bpf_reg_state *reg, int regno)
+int check_ptr_off_reg(struct bpf_verifier_env *env,
+		      const struct bpf_reg_state *reg, int regno)
 {
-	/* Access to ctx or passing it to a helper is only allowed in
-	 * its original, unmodified form.
+	/* Access to this pointer-typed register or passing it to a helper
+	 * is only allowed in its original, unmodified form.
 	 */
 
 	if (reg->off) {
-		verbose(env, "dereference of modified ctx ptr R%d off=%d disallowed\n",
-			regno, reg->off);
+		verbose(env, "dereference of modified %s ptr R%d off=%d disallowed\n",
+			reg_type_str(env, reg->type), regno, reg->off);
 		return -EACCES;
 	}
 
 	if (!tnum_is_const(reg->var_off) || reg->var_off.value) {
 		char tn_buf[48];
 
 		tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off);
-		verbose(env, "variable ctx access var_off=%s disallowed\n", tn_buf);
+		verbose(env, "variable %s access var_off=%s disallowed\n",
+			reg_type_str(env, reg->type), tn_buf);
 		return -EACCES;
 	}
 
@@ -4114,7 +4115,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
 			return -EACCES;
 		}
 
-		err = check_ctx_reg(env, reg, regno);
+		err = check_ptr_off_reg(env, reg, regno);
 		if (err < 0)
 			return err;
 
@@ -4926,7 +4927,7 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 		return err;
 
 	if (type == PTR_TO_CTX) {
-		err = check_ctx_reg(env, reg, regno);
+		err = check_ptr_off_reg(env, reg, regno);
 		if (err < 0)
 			return err;
 	}
@@ -9069,7 +9070,7 @@ static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn)
 			return err;
 	}
 
-	err = check_ctx_reg(env, &regs[ctx_reg], ctx_reg);
+	err = check_ptr_off_reg(env, &regs[ctx_reg], ctx_reg);
 	if (err < 0)
 		return err;