Re: [PATCH] lib/buildid: Handle memfd_secret() files in build_id_parse()

[Chen Linxuan]

On Thu, Mar 06, 2025 at 03:08:11PM -0800, Andrew Morton wrote:
> On Thu,  6 Mar 2025 13:06:58 +0800 Chen Linxuan <chenlinxuan@xxxxxxxxxx> wrote:
> 
> > Backport of a similar change from commit 5ac9b4e935df ("lib/buildid:
> > Handle memfd_secret() files in build_id_parse()") to address an issue
> > where accessing secret memfd contents through build_id_parse() would
> > trigger faults.
> > 
> > Original report and repro can be found in [0].
> > 
> >   [0] https://lore.kernel.org/bpf/ZwyG8Uro%2FSyTXAni@ly-workstation/
> > 
> > This repro will cause BUG: unable to handle kernel paging request in
> > build_id_parse in 5.15/6.1/6.6.
> > 
> > ...
> >
> > --- a/lib/buildid.c
> > +++ b/lib/buildid.c
> > @@ -157,6 +157,12 @@ int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
> >  	if (!vma->vm_file)
> >  		return -EINVAL;
> >  
> > +#ifdef CONFIG_SECRETMEM
> > +	/* reject secretmem folios created with memfd_secret() */
> > +	if (vma->vm_file->f_mapping->a_ops == &secretmem_aops)
> > +		return -EFAULT;
> > +#endif
> > +
> >  	page = find_get_page(vma->vm_file->f_mapping, 0);
> >  	if (!page)
> >  		return -EFAULT;	/* page not mapped */
> 
> Please redo this against a current kernel?  build_id_parse() has
> changed a lot.

stable/linux-6.13.y and stable/linux-6.12.y has commit 5ac9b4e935df
("lib/buildid: Handle memfd_secret() files in build_id_parse()").

stable/linux-5.10.y and stable/linux-5.4.y do not have memfd_secret(2) feature,
so this patch is not needed.

> 
>