From d6b732666a1bae0df3c3ae06925043bba34502b1 Mon Sep 17 00:00:00 2001
From: Masahiro Yamada <masahiroy@kernel.org>
Date: Tue, 24 May 2022 01:46:22 +0900
Subject: [PATCH] modpost: fix undefined behavior of is_arm_mapping_symbol()
Git-commit: d6b732666a1bae0df3c3ae06925043bba34502b1
Patch-mainline: v5.19-rc1
References: git-fixes

The return value of is_arm_mapping_symbol() is unpredictable when "$"
is passed in.

strchr(3) says:
  The strchr() and strrchr() functions return a pointer to the matched
  character or NULL if the character is not found. The terminating null
  byte is considered part of the string, so that if c is specified as
  '\0', these functions return a pointer to the terminator.

When str[1] is '\0', strchr("axtd", str[1]) is not NULL, and str[2] is
referenced (i.e. buffer overrun).

Test code

Acked-by: Takashi Iwai <tiwai@suse.de>

---------

  char str1[] = "abc";
  char str2[] = "ab";

  strcpy(str1, "$");
  strcpy(str2, "$");

  printf("test1: %d\n", is_arm_mapping_symbol(str1));
  printf("test2: %d\n", is_arm_mapping_symbol(str2));

Result
------

  test1: 0
  test2: 1

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
---
 scripts/mod/modpost.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 08f6989437bd..1092906867f0 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1180,7 +1180,8 @@ static int secref_whitelist(const struct sectioncheck *mismatch,
 
 static inline int is_arm_mapping_symbol(const char *str)
 {
-	return str[0] == '$' && strchr("axtd", str[1])
+	return str[0] == '$' &&
+	       (str[1] == 'a' || str[1] == 'd' || str[1] == 't' || str[1] == 'x')
 	       && (str[2] == '\0' || str[2] == '.');
 }
 
-- 
2.35.3