bfd_get_symbol_leading_char vs. ""

[Alan Modra]

Some places matching the first char of a string against
bfd_get_symbol_leading_char, which may be zero, didn't check for the
string being "".  This patch adds the check to stop accesses past the
end of the string and potential buffer overruns.
The dlltool one was found by oss-fuzz quite a while ago.

bfd/
	* cofflink.c (_bfd_coff_link_input_bfd): Ensure a zero
	bfd_get_symbol_leading_char doesn't lead to accessing past the
	zero string terminator.
	* linker.c (bfd_wrapped_link_hash_lookup): Likewise.
	(unwrap_hash_lookup): Likewise.
binutils/
	* dlltool.c (scan_filtered_symbols): Ensure a zero
	bfd_get_symbol_leading_char doesn't lead to accessing past the
	zero string terminator.

diff --git a/bfd/cofflink.c b/bfd/cofflink.c
index aea5c4c38a5..221f6e8183a 100644
--- a/bfd/cofflink.c
+++ b/bfd/cofflink.c
@@ -1618,7 +1618,8 @@ _bfd_coff_link_input_bfd (struct coff_final_link_info *flaginfo, bfd *input_bfd)
 	  /* Ignore fake names invented by compiler; treat them all as
 	     the same name.  */
 	  if (*name == '~' || *name == '.' || *name == '$'
-	      || (*name == bfd_get_symbol_leading_char (input_bfd)
+	      || (*name
+		  && *name == bfd_get_symbol_leading_char (input_bfd)
 		  && (name[1] == '~' || name[1] == '.' || name[1] == '$')))
 	    name = "";
 
diff --git a/bfd/linker.c b/bfd/linker.c
index 0f4f9a1776c..28fffc3ad63 100644
--- a/bfd/linker.c
+++ b/bfd/linker.c
@@ -544,7 +544,9 @@ bfd_wrapped_link_hash_lookup (bfd *abfd,
       char prefix = '\0';
 
       l = string;
-      if (*l == bfd_get_symbol_leading_char (abfd) || *l == info->wrap_char)
+      if (*l
+	  && (*l == bfd_get_symbol_leading_char (abfd)
+	      || *l == info->wrap_char))
 	{
 	  prefix = *l;
 	  ++l;
@@ -621,8 +623,9 @@ unwrap_hash_lookup (struct bfd_link_info *info,
 {
   const char *l = h->root.string;
 
-  if (*l == bfd_get_symbol_leading_char (input_bfd)
-      || *l == info->wrap_char)
+  if (*l
+      && (*l == bfd_get_symbol_leading_char (input_bfd)
+	  || *l == info->wrap_char))
     ++l;
 
   if (startswith (l, WRAP))
diff --git a/binutils/dlltool.c b/binutils/dlltool.c
index 085d4c2ce41..6d63e11e084 100644
--- a/binutils/dlltool.c
+++ b/binutils/dlltool.c
@@ -1500,7 +1500,8 @@ scan_filtered_symbols (bfd *abfd, void *minisyms, long symcount,
 	bfd_fatal (bfd_get_filename (abfd));
 
       symbol_name = bfd_asymbol_name (sym);
-      if (bfd_get_symbol_leading_char (abfd) == symbol_name[0])
+      if (*symbol_name
+	  && *symbol_name == bfd_get_symbol_leading_char (abfd))
 	++symbol_name;
 
       def_exports (xstrdup (symbol_name) , 0, -1, 0, 0,

-- 
Alan Modra
Australia Development Lab, IBM