From: Daniel Borkmann <daniel@iogearbox.net>
Date: Wed, 24 Mar 2021 11:25:39 +0100
Subject: bpf: Move sanitize_val_alu out of op switch
Patch-mainline: v5.12-rc8
Git-commit: f528819334881fd622fdadeddb3f7edaed8b7c9b
References: bsc#1184942 CVE-2021-29155

Add a small sanitize_needed() helper function and move sanitize_val_alu()
out of the main opcode switch. In upcoming work, we'll move sanitize_ptr_alu()
as well out of its opcode switch so this helps to streamline both.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Gary Lin <glin@suse.com>

NOTE from Gary:
  * The diffs for adjust_scalar_min_max_vals(_ are modified to fit
    cve/linux-4.12.

---
 kernel/bpf/verifier.c |   15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1999,6 +1999,11 @@ static int sanitize_val_alu(struct bpf_v
 	return update_alu_sanitation_state(aux, BPF_ALU_NON_POINTER, 0);
 }
 
+static bool sanitize_needed(u8 opcode)
+{
+	return opcode == BPF_ADD || opcode == BPF_SUB;
+}
+
 static int sanitize_ptr_alu(struct bpf_verifier_env *env,
 			    struct bpf_insn *insn,
 			    const struct bpf_reg_state *ptr_reg,
@@ -2420,11 +2425,14 @@ static int adjust_scalar_min_max_vals(st
 		return 0;
 	}
 
-	switch (opcode) {
-	case BPF_ADD:
+	if (sanitize_needed(opcode)) {
 		ret = sanitize_val_alu(env, insn);
 		if (ret < 0)
 			return sanitize_err(env, insn, ret, NULL, NULL);
+	}
+
+	switch (opcode) {
+	case BPF_ADD:
 		if (signed_add_overflows(dst_reg->smin_value, smin_val) ||
 		    signed_add_overflows(dst_reg->smax_value, smax_val)) {
 			dst_reg->smin_value = S64_MIN;
@@ -2444,9 +2452,6 @@ static int adjust_scalar_min_max_vals(st
 		dst_reg->var_off = tnum_add(dst_reg->var_off, src_reg.var_off);
 		break;
 	case BPF_SUB:
-		ret = sanitize_val_alu(env, insn);
-		if (ret < 0)
-			return sanitize_err(env, insn, ret, NULL, NULL);
 		if (signed_sub_overflows(dst_reg->smin_value, smax_val) ||
 		    signed_sub_overflows(dst_reg->smax_value, smin_val)) {
 			/* Overflow possible, we know nothing */