Re: [PATCH] grub-file: fix segmentation fault

[Andrei Borzenkov]

08.04.2016 09:43, Michael Chang пишет:
> 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.
> 

This now makes filename unavailable to progress module (which gets the
last grub_file in a chain) and it still does not cover corner case of
failing grub_strdup in grub_file_open.

Fixing the former requires some redesign. But as long as we allow
filename to remain empty in grub_file_open every user must explicitly
check for it being NULL.

> 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));
>  
>