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SubjectRe: [PATCH] mm/gup: fix null pointer dereference detected by coverity
On Tue, Apr 07, 2020 at 05:51:07PM +0800, Miles Chen 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);
> ...
> }
>
> Fixes: 4a9e1cda2748 ("mm: bring in additional flag for fixup_user_fault to signal unlock")
> Signed-off-by: Miles Chen <miles.chen@mediatek.com>

Reviewed-by: Ira Weiny <ira.weiny@intel.com>

> ---
> mm/gup.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index da3e03185144..a68d11dc232d 100644
> --- 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;
> }
> --
> 2.18.0

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