Re: [PATCH] xfs: mark sb_fname as nonstring
From: Eric Sandeen
Date: Tue Jun 05 2018 - 17:51:50 EST
On 6/5/18 4:23 PM, Arnd Bergmann wrote:
> On Tue, Jun 5, 2018 at 8:44 PM, Eric Sandeen <sandeen@xxxxxxxxxxx> wrote:
>> On 5/25/18 10:14 AM, Arnd Bergmann wrote:
>>> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
>>> index 84fbf164cbc3..eb79f2bc4dcc 100644
>>> --- a/fs/xfs/xfs_ioctl.c
>>> +++ b/fs/xfs/xfs_ioctl.c
>>> @@ -1819,12 +1819,12 @@ xfs_ioc_getlabel(
>>> BUILD_BUG_ON(sizeof(sbp->sb_fname) > FSLABEL_MAX);
>>> - strncpy(label, sbp->sb_fname, sizeof(sbp->sb_fname));
>>> + strncpy(label, sbp->sb_fname, XFSLABEL_MAX);
>>> /* xfs on-disk label is 12 chars, be sure we send a null to user */
>>> label[XFSLABEL_MAX] = '\0';
>>> - if (copy_to_user(user_label, label, sizeof(sbp->sb_fname)))
>>> + if (copy_to_user(user_label, label, sizeof(label)))
>> I /think/ this also runs the risk of copying out stack memory.
>> I'll send another proposal based on this with slight modifications.
> I assumed it's safe since the earlier strncpy() pads the local 'label'
> with zero bytes up the XFSLABEL_MAX, and the last byte
> is explicitly set to guarantee zero padding.
Ah you are right, I forgot that strncpy pads. Did I mention that I hate
C strings... o_O
In that case I suppose your original patch is fine, if you'd like to fix
the "mark as nonstring" subject.