Re: [PATCH] Avoid NULL pointer dereference in progress module.

[Andrei Borzenkov <arvidjaar@gmail.com>]

21.09.2015 18:11, Dann Frazier пишет:
> On Fri, Aug 21, 2015 at 8:24 AM, Dann Frazier
> <dann.frazier@canonical.com> wrote:
>> On Thu, Aug 20, 2015 at 11:55 AM, Andrei Borzenkov <arvidjaar@gmail.com> wrote:
>>> 18.08.2015 00:57, dann frazier пишет:
>>>>
>>>> grub_net_fs_open() saves off a copy of the file structure it gets passed
>>>> and
>>>> uses it to create a bufio structure. It then overwrites the passed in file
>>>> structure with this new bufio structure. Since file->name doesn't get set
>>>> until we return back to grub_file_open(), it means that only the bufio
>>>> structure gets a valid file->name. The "real" file's name is left
>>>> uninitialized. This leads to a crash when the progress module hook is
>>>> called
>>>> on it. Fix this by adding a copy of the filename during the switcheroo.
>>>
>>>
>>> Actually name was already saved off as device->net-name. What about attached
>>> patch? I'll commit leak fix separately.
>>
>> It does seem like it pokes a hole in the fs abstraction, but it works for me.
>
> hey Andrei,
>   Did you need anything more from me wrt this fix?
>

Sorry for delay. We already need to differentiate between disk and net 
files in other places anyway. So I think it is OK as a simple fix. I 
committed it.

May be bufio needs to be converted to filter but this is too intrusive 
for this.

>   -dann
>
>>>
>>>> grub_file_close() will free that string in the success case, we only need
>>>> to handle the free in an error. While we're at it, also fix a leaked file
>>>> structure in the case that grub_strdup() fails when setting
>>>> file->device->net->name.
>>>>
>>>> Finally, make progress more robust by checking for NULL before reading the
>>>> name. Andrei noticed that this could occur if grub_strdup() fails in
>>>> grub_file_open().
>>>>
>>>> Signed-off-by: dann frazier <dann.frazier@canonical.com>
>>>> ---
>>>>    grub-core/lib/progress.c |  3 +--
>>>>    grub-core/net/net.c      | 14 +++++++++++++-
>>>>    2 files changed, 14 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/grub-core/lib/progress.c b/grub-core/lib/progress.c
>>>> index 63a0767..2775554 100644
>>>> --- a/grub-core/lib/progress.c
>>>> +++ b/grub-core/lib/progress.c
>>>> @@ -70,8 +70,7 @@ grub_file_progress_hook_real (grub_disk_addr_t sector
>>>> __attribute__ ((unused)),
>>>>          percent = grub_divmod64 (100 * file->progress_offset,
>>>>                                   file->size, 0);
>>>>
>>>> -      partial_file_name = grub_strrchr (file->name, '/');
>>>> -      if (partial_file_name)
>>>> +      if (file->name && (partial_file_name = grub_strrchr (file->name,
>>>> '/')))
>>>>          partial_file_name++;
>>>>          else
>>>>          partial_file_name = "";
>>>> diff --git a/grub-core/net/net.c b/grub-core/net/net.c
>>>> index 21a4e94..9f83765 100644
>>>> --- a/grub-core/net/net.c
>>>> +++ b/grub-core/net/net.c
>>>> @@ -1391,7 +1391,17 @@ grub_net_fs_open (struct grub_file *file_out, const
>>>> char *name)
>>>>      file->device->net->packs.last = NULL;
>>>>      file->device->net->name = grub_strdup (name);
>>>>      if (!file->device->net->name)
>>>> -    return grub_errno;
>>>> +    {
>>>> +      grub_free (file);
>>>> +      return grub_errno;
>>>> +    }
>>>> +  file->name = grub_strdup (name);
>>>> +  if (!file->name)
>>>> +    {
>>>> +      grub_free (file->device->net->name);
>>>> +      grub_free (file);
>>>> +      return grub_errno;
>>>> +    }
>>>>
>>>>      err = file->device->net->protocol->open (file, name);
>>>>      if (err)
>>>> @@ -1401,6 +1411,7 @@ grub_net_fs_open (struct grub_file *file_out, const
>>>> char *name)
>>>>            grub_netbuff_free (file->device->net->packs.first->nb);
>>>>            grub_net_remove_packet (file->device->net->packs.first);
>>>>          }
>>>> +      grub_free (file->name);
>>>>          grub_free (file->device->net->name);
>>>>          grub_free (file);
>>>>          return err;
>>>> @@ -1414,6 +1425,7 @@ grub_net_fs_open (struct grub_file *file_out, const
>>>> char *name)
>>>>            grub_net_remove_packet (file->device->net->packs.first);
>>>>          }
>>>>          file->device->net->protocol->close (file);
>>>> +      grub_free (file->name);
>>>>          grub_free (file->device->net->name);
>>>>          grub_free (file);
>>>>          return grub_errno;
>>>>
>>>