[PATCH] grub-file: fix segmentation fault

[Michael Chang]

In grub_file_open the file handle returned by file filters has no file->name
set which leads to segmentation fault later referenced by grub_elf_file. We
move the file->name value assignment after file filters to make sure it will be
set and returned.

The stack backtrace for reference.

 gdb --args ./grub-file --is-x86_64-xen-domu /boot/vmlinux-4.1.12-1-default.gz

 (gdb) bt
 #0  0x000000000047597e in grub_strlen (s=0x0) at ../grub-core/kern/misc.c:558
 #1  0x00000000004757e2 in grub_strdup (s=0x0) at ../grub-core/kern/misc.c:463
 #2  0x0000000000406418 in grub_elf_file (file=0x6dfb50, filename=0x0) at 
../grub-core/kern/elf.c:89
 #3  0x00000000004043b3 in grub_xen_file (file=0x6dfb50) at 
../grub-core/loader/i386/xen_file.c:29
 #4  0x0000000000403930 in grub_cmd_file (ctxt=0x7fffffffe120, argc=1, 
args=0x6dfa00) at ../grub-core/commands/file.c:425
 #5  0x000000000047e178 in grub_extcmd_dispatcher (cmd=0x6df730, argc=2, 
args=0x6ddfb0, script=0x0) at ../grub-core/commands/extcmd.c:54
 #6  0x000000000047e1d7 in grub_extcmd_dispatch (cmd=0x6df730, argc=2, 
args=0x6ddfb0) at ../grub-core/commands/extcmd.c:67
 #7  0x0000000000402945 in main (argc=3, argv=0x7fffffffe2e8) at 
../util/grub-file.c:102
 (gdb) frame 3
 #3  0x00000000004043b3 in grub_xen_file (file=0x6dfb50) at 
../grub-core/loader/i386/xen_file.c:29
 29        elf = grub_elf_file (file, file->name);
---
 grub-core/kern/file.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/grub-core/kern/file.c b/grub-core/kern/file.c
index 668f893..44047d7 100644
--- a/grub-core/kern/file.c
+++ b/grub-core/kern/file.c
@@ -111,9 +111,6 @@ grub_file_open (const char *name)
   if ((file->fs->open) (file, file_name) != GRUB_ERR_NONE)
     goto fail;
 
-  file->name = grub_strdup (name);
-  grub_errno = GRUB_ERR_NONE;
-
   for (filter = 0; file && filter < ARRAY_SIZE (grub_file_filters_enabled);
        filter++)
     if (grub_file_filters_enabled[filter])
@@ -123,7 +120,12 @@ grub_file_open (const char *name)
       }
   if (!file)
     grub_file_close (last_file);
-    
+  else
+    {
+      file->name = grub_strdup (name);
+      grub_errno = GRUB_ERR_NONE;
+    }
+
   grub_memcpy (grub_file_filters_enabled, grub_file_filters_all,
               sizeof (grub_file_filters_enabled));
 
-- 
2.6.2