Messages in this thread | | | Date | Tue, 14 Apr 2020 17:08:27 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] mm/gup: fix null pointer dereference detected by coverity |
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On Tue, 7 Apr 2020 17:51:07 +0800 Miles Chen <miles.chen@mediatek.com> wrote:
> In fixup_user_fault(), it is possible that unlocked is NULL, > so we should test unlocked before using it. > > For example, in arch/arc/kernel/process.c, NULL is passed > to fixup_user_fault(). > > SYSCALL_DEFINE3(arc_usr_cmpxchg, int *, uaddr, int, expected, int, new) > { > ... > ret = fixup_user_fault(current, current->mm, (unsigned long) uaddr, > FAULT_FLAG_WRITE, NULL); > ... > }
(cc Peter)
> --- a/mm/gup.c > +++ b/mm/gup.c > @@ -1230,7 +1230,8 @@ int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm, > if (ret & VM_FAULT_RETRY) { > down_read(&mm->mmap_sem); > if (!(fault_flags & FAULT_FLAG_TRIED)) { > - *unlocked = true; > + if (unlocked) > + *unlocked = true; > fault_flags |= FAULT_FLAG_TRIED; > goto retry; > }
Not sure. If the caller passes FAULT_FLAG_ALLOW_RETRY then they must also pass in a valid non-NULL `unlocked'. If the caller passed FAULT_FLAG_ALLOW_RETRY and unlocked==NULL then the resulting oops is an appropriate way of reporting this mistake. I think?
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