mm/gup: fix null pointer dereference detected by coverity
diff mbox series

Message ID 20200407095107.1988-1-miles.chen@mediatek.com
State New
Headers show
Series
  • mm/gup: fix null pointer dereference detected by coverity
Related show

Commit Message

Miles Chen April 7, 2020, 9:51 a.m. UTC
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>
---
 mm/gup.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Ira Weiny April 7, 2020, 6:19 p.m. UTC | #1
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
Souptick Joarder April 14, 2020, 7:55 p.m. UTC | #2
On Tue, Apr 7, 2020 at 11:49 PM Ira Weiny <ira.weiny@intel.com> wrote:
>
> 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>

Acked-by: Souptick Joarder <jrdr.linux@gmail.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
>
Andrew Morton April 15, 2020, 12:08 a.m. UTC | #3
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?
Miles Chen April 15, 2020, 1:53 a.m. UTC | #4
On Tue, 2020-04-14 at 17:08 -0700, Andrew Morton wrote:
> 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?
> 
Agree. How about put "unlocked==NULL must not be used with
FAULT_FLAG_ALLOW_RETRY." in the comment? Make it easier to understand
the oops.

e.g., 

--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1176,7 +1176,8 @@ static bool vma_permits_fault(struct
vm_area_struct *vma,
  * @address:   user address
  * @fault_flags:flags to pass down to handle_mm_fault()
  * @unlocked:  did we unlock the mmap_sem while retrying, maybe NULL if
caller
- *             does not allow retry
+ *             does not allow retry. If NULL, the caller must guarantee
+ *             the fault_flags does not contain FAULT_FLAG_ALLOW_RETRY.

Patch
diff mbox series

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;
 		}