Fix potential NULL pointer dereference

This patch addresses a potential NULL pointer dereference when we try to
duplicate a string. The input pointer can be NULL and that may lead to
crashes. We simply add a check for that case.

gdb/ChangeLog:
2016-10-24  Luis Machado  <lgustavo@codesourcery.com>

	* exec.c (exec_file_locate_attach): Prevent NULL pointer dereference
	when duplicating a string.

2 files changed, 7 insertions, 1 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 388cc1f..43175ff 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,10 @@
 2016-10-24  Luis Machado  <lgustavo@codesourcery.com>
 
+	* exec.c (exec_file_locate_attach): Prevent NULL pointer dereference
+	when duplicating a string.
+
+2016-10-24  Luis Machado  <lgustavo@codesourcery.com>
+
 	* exec.c (exception_print_same): Fix string comparison to use
 	statically-allocated ones.
 
diff --git a/gdb/exec.c b/gdb/exec.c
index 67ecc63..6e2a296 100644
--- a/gdb/exec.c
+++ b/gdb/exec.c
@@ -227,7 +227,8 @@ exec_file_locate_attach (int pid, int defer_bp_reset, int from_tty)
       prev_err = err;
 
       /* Save message so it doesn't get trashed by the catch below.  */
-      prev_err.message = xstrdup (err.message);
+      if (err.message != NULL)
+	prev_err.message = xstrdup (err.message);
     }
   END_CATCH