Re: [PATCH] kernfs: fix potential null-ptr-deref in kernfs_path_from_node_locked()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Sat, Nov 26, 2022 at 05:49:50PM +0800, Leizhen (ThunderTown) wrote:
> 
> 
> On 2022/11/24 10:52, Leizhen (ThunderTown) wrote:
> > 
> > 
> > On 2022/11/24 10:28, Leizhen (ThunderTown) wrote:
> >>
> >>
> >> On 2022/11/24 10:24, Leizhen (ThunderTown) wrote:
> >>>
> >>>
> >>> On 2022/11/24 0:55, Tejun Heo wrote:
> >>>> On Wed, Nov 23, 2022 at 10:04:19AM +0800, Zhen Lei wrote:
> >>>>> Ensure that the 'buf' is not empty before strlcpy() uses it.
> >>>>>
> >>>>> Commit bbe70e4e4211 ("fs: kernfs: Fix possible null-pointer dereferences
> >>>>> in kernfs_path_from_node_locked()") first noticed this, but it didn't
> >>>>> fix it completely.
> >>>>>
> >>>>> Fixes: 9f6df573a404 ("kernfs: Add API to generate relative kernfs path")
> >>>>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> >>>>
> >>>> I think the right thing to do is removing that if. It makes no sense to call
> >>>> that function with NULL buf and the fact that nobody reported crashes on
> >>>> NULL buf indicates that we in fact never do.
> 
> kernfs_path_from_node
>     -->kernfs_path_from_node_locked
> 
> EXPORT_SYMBOL_GPL(kernfs_path_from_node)
> 
> I've rethought it. The export APIs need to do null pointer check, right?

No, callers should get this right.  Are there any in-tree ones that do
not?

thanks,

greg k-h