Re: [PATCH v3] Fixes: null pointer dereference in pfnmap_lockdep_assert

[Manas]

Hi Matthew,

On 04.10.2024 16:17, Matthew Wilcox wrote:
> On Fri, Oct 04, 2024 at 07:15:48PM +0530, Manas via B4 Relay wrote:
> > +++ b/mm/memory.c
> > @@ -6346,10 +6346,10 @@ static inline void pfnmap_args_setup(struct follow_pfnmap_args *args,
> >  static inline void pfnmap_lockdep_assert(struct vm_area_struct *vma)
> >  {
> >  #ifdef CONFIG_LOCKDEP
> > -	struct address_space *mapping = vma->vm_file->f_mapping;
> > +	struct address_space *mapping = vma->vm_file ? vma->vm_file->f_mapping : NULL;
>
> Overly long and complex line.  Much simpler to write:
>
> 	struct address_space *mapping = NULL;
>
> 	if (vma->vm_file)
> 		mapping = vma->vm_file->f_mapping;
Thank you for reviewing! I am sending v4.

> >  	if (mapping)
> > -		lockdep_assert(lockdep_is_held(&vma->vm_file->f_mapping->i_mmap_rwsem) ||
> > +		lockdep_assert(lockdep_is_held(&mapping->i_mmap_rwsem) ||
> >  			       lockdep_is_held(&vma->vm_mm->mmap_lock));
> >  	else
> >  		lockdep_assert(lockdep_is_held(&vma->vm_mm->mmap_lock));
>
> This one should have been lockdep_assert_held(&vma->vm_mm->mmap_lock).
>
> I'm not sure that the previous one is correct.  The
> lockdep_assert_held() macro is pretty careful about checking
> LOCK_STATE_NOT_HELD to avoid the LOCK_STATE_UNKNOWN possibility.
> But I'll leave that for Peter to fix.

--
Manas