[PATCH 3/3] x86/insn-eval: Fix not using prefixes.nbytes for loop over prefixes.bytes

[Masami Hiramatsu]

Since the insn.prefixes.nbytes can be bigger than the size of
insn.prefixes.bytes[] when a same prefix is repeated, we have to
check whether the insn.prefixes.bytes[i] != 0 and i < 4 instead
of insn.prefixes.nbytes.

Fixes: 32d0b95300db ("x86/insn-eval: Add utility functions to get segment selector")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
 arch/x86/lib/insn-eval.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 58f7fb95c7f4..c52c91461f52 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -67,7 +67,7 @@ bool insn_has_rep_prefix(struct insn *insn)
 
 	insn_get_prefixes(insn);
 
-	for (i = 0; i < insn->prefixes.nbytes; i++) {
+	for (i = 0; insn->prefixes.bytes[i] && i < 4; i++) {
 		insn_byte_t p = insn->prefixes.bytes[i];
 
 		if (p == 0xf2 || p == 0xf3)
@@ -99,7 +99,7 @@ static int get_seg_reg_override_idx(struct insn *insn)
 	insn_get_prefixes(insn);
 
 	/* Look for any segment override prefixes. */
-	for (i = 0; i < insn->prefixes.nbytes; i++) {
+	for (i = 0; insn->prefixes.bytes[i] && i < 4; i++) {
 		insn_attr_t attr;
 
 		attr = inat_get_opcode_attribute(insn->prefixes.bytes[i]);