2020-04-07 09:53:12

by Miles Chen

Subject: [PATCH] mm/gup: fix null pointer dereference detected by coverity

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 <[email protected]>
---
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

2020-04-07 18:20:11

by Ira Weiny

Subject: Re: [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 <[email protected]>

Reviewed-by: Ira Weiny <[email protected]>

> ---
> 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

2020-04-15 14:48:07

by Miles Chen

Subject: Re: [PATCH] mm/gup: fix null pointer dereference detected by coverity

On Tue, 2020-04-14 at 17:08 -0700, Andrew Morton wrote:
> On Tue, 7 Apr 2020 17:51:07 +0800 Miles Chen <[email protected]> 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.

2020-04-15 21:54:00

by Souptick Joarder

Subject: Re: [PATCH] mm/gup: fix null pointer dereference detected by coverity

On Tue, Apr 7, 2020 at 11:49 PM Ira Weiny <[email protected]> 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 <[email protected]>
>
> Reviewed-by: Ira Weiny <[email protected]>

Acked-by: Souptick Joarder <[email protected]>

>
> > ---
> > 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
>

2020-04-15 21:59:18

by Andrew Morton

Subject: Re: [PATCH] mm/gup: fix null pointer dereference detected by coverity

On Tue, 7 Apr 2020 17:51:07 +0800 Miles Chen <[email protected]> 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?