From: Masahiro Yamada <masahiroy@kernel.org>
Date: Mon, 23 May 2022 16:46:22 +0000 (+0900)
Subject: modpost: fix undefined behavior of is_arm_mapping_symbol()
X-Git-Tag: v5.19-rc1~17^2~21
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=d6b732666a1b;p=thirdparty%2Flinux.git

modpost: fix undefined behavior of is_arm_mapping_symbol()

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
---------

  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>
---

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 08f6989437bd9..1092906867f00 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] == '.');
 }