Fix read-beyond-end-of-buffer error in script parsing.

2016-12-19  Cary Coutant  <ccoutant@gmail.com>

gold/
	PR gold/20949
	* script.cc (Lex::get_token): Don't look ahead past NUL characters.

1 files changed, 21 insertions, 14 deletions

diff --git a/gold/script.cc b/gold/script.cc
index bb8b437..e4d0593 100644
--- a/gold/script.cc
+++ b/gold/script.cc
@@ -764,12 +764,6 @@ Lex::get_token(const char** pp)
 
   while (true)
     {
-      if (*p == '\0')
-	{
-	  *pp = p;
-	  return this->make_eof_token(p);
-	}
-
       // Skip whitespace quickly.
       while (*p == ' ' || *p == '\t' || *p == '\r')
 	++p;
@@ -782,8 +776,18 @@ Lex::get_token(const char** pp)
 	  continue;
 	}
 
+      char c0 = *p;
+
+      if (c0 == '\0')
+	{
+	  *pp = p;
+	  return this->make_eof_token(p);
+	}
+
+      char c1 = p[1];
+
       // Skip C style comments.
-      if (p[0] == '/' && p[1] == '*')
+      if (c0 == '/' && c1 == '*')
 	{
 	  int lineno = this->lineno_;
 	  int charpos = p - this->linestart_ + 1;
@@ -797,7 +801,7 @@ Lex::get_token(const char** pp)
 	}
 
       // Skip line comments.
-      if (*p == '#')
+      if (c0 == '#')
 	{
 	  *pp = p + 1;
 	  if (!this->skip_line_comment(pp))
@@ -807,7 +811,7 @@ Lex::get_token(const char** pp)
 	}
 
       // Check for a name.
-      if (this->can_start_name(p[0], p[1]))
+      if (this->can_start_name(c0, c1))
 	return this->gather_token(Token::TOKEN_STRING,
 				  &Lex::can_continue_name,
 				  p, p + 1, pp);
@@ -820,35 +824,38 @@ Lex::get_token(const char** pp)
 	  return this->gather_quoted_string(pp);
 	}
 
+      // Be careful not to lookahead past the end of the buffer.
+      char c2 = (c1 == '\0' ? '\0' : p[2]);
+
       // Check for a number.
 
-      if (this->can_start_hex(p[0], p[1], p[2]))
+      if (this->can_start_hex(c0, c1, c2))
 	return this->gather_token(Token::TOKEN_INTEGER,
 				  &Lex::can_continue_hex,
 				  p, p + 3, pp);
 
-      if (Lex::can_start_number(p[0]))
+      if (Lex::can_start_number(c0))
 	return this->gather_token(Token::TOKEN_INTEGER,
 				  &Lex::can_continue_number,
 				  p, p + 1, pp);
 
       // Check for operators.
 
-      int opcode = Lex::three_char_operator(p[0], p[1], p[2]);
+      int opcode = Lex::three_char_operator(c0, c1, c2);
       if (opcode != 0)
 	{
 	  *pp = p + 3;
 	  return this->make_token(opcode, p);
 	}
 
-      opcode = Lex::two_char_operator(p[0], p[1]);
+      opcode = Lex::two_char_operator(c0, c1);
       if (opcode != 0)
 	{
 	  *pp = p + 2;
 	  return this->make_token(opcode, p);
 	}
 
-      opcode = Lex::one_char_operator(p[0]);
+      opcode = Lex::one_char_operator(c0);
       if (opcode != 0)
 	{
 	  *pp = p + 1;