* [PATCH] mm/gup.c: Handling ERR within unpin_user_pages()
@ 2020-09-13 14:32 Souptick Joarder
2020-09-13 14:55 ` Matthew Wilcox
0 siblings, 1 reply; 7+ messages in thread
From: Souptick Joarder @ 2020-09-13 14:32 UTC (permalink / raw)
To: akpm; +Cc: linux-mm, linux-kernel, Souptick Joarder, John Hubbard
It is possible that a buggy caller of unpin_user_pages()
(specially in error handling path) may end up calling it with
npages < 0 which is unnecessary.
This can be fixed by adding extra check inside unpin_user_pages().
Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Cc: John Hubbard <jhubbard@nvidia.com>
---
mm/gup.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/mm/gup.c b/mm/gup.c
index 0b5c308b..2e19bd6 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -328,6 +328,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
{
unsigned long index;
+ if (WARN_ON_ONCE(npages < 0))
+ return;
+
/*
* TODO: this can be optimized for huge pages: if a series of pages is
* physically contiguous and part of the same compound page, then a
--
1.9.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] mm/gup.c: Handling ERR within unpin_user_pages()
2020-09-13 14:32 [PATCH] mm/gup.c: Handling ERR within unpin_user_pages() Souptick Joarder
@ 2020-09-13 14:55 ` Matthew Wilcox
2020-09-14 1:50 ` Souptick Joarder
0 siblings, 1 reply; 7+ messages in thread
From: Matthew Wilcox @ 2020-09-13 14:55 UTC (permalink / raw)
To: Souptick Joarder; +Cc: akpm, linux-mm, linux-kernel, John Hubbard
On Sun, Sep 13, 2020 at 08:02:35PM +0530, Souptick Joarder wrote:
> It is possible that a buggy caller of unpin_user_pages()
> (specially in error handling path) may end up calling it with
> npages < 0 which is unnecessary.
> @@ -328,6 +328,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
> {
> unsigned long index;
>
> + if (WARN_ON_ONCE(npages < 0))
> + return;
But npages is unsigned long. So it can't be less than zero.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm/gup.c: Handling ERR within unpin_user_pages()
2020-09-13 14:55 ` Matthew Wilcox
@ 2020-09-14 1:50 ` Souptick Joarder
2020-09-14 14:08 ` Jason Gunthorpe
0 siblings, 1 reply; 7+ messages in thread
From: Souptick Joarder @ 2020-09-14 1:50 UTC (permalink / raw)
To: Matthew Wilcox; +Cc: Andrew Morton, Linux-MM, linux-kernel, John Hubbard
On Sun, Sep 13, 2020 at 8:25 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Sun, Sep 13, 2020 at 08:02:35PM +0530, Souptick Joarder wrote:
> > It is possible that a buggy caller of unpin_user_pages()
> > (specially in error handling path) may end up calling it with
> > npages < 0 which is unnecessary.
> > @@ -328,6 +328,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
> > {
> > unsigned long index;
> >
> > + if (WARN_ON_ONCE(npages < 0))
> > + return;
>
> But npages is unsigned long. So it can't be less than zero.
Sorry, I missed it.
Then, it means if npages is assigned with -ERRNO by caller, unpin_user_pages()
may end up calling a big loop, which is unnecessary.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm/gup.c: Handling ERR within unpin_user_pages()
2020-09-14 1:50 ` Souptick Joarder
@ 2020-09-14 14:08 ` Jason Gunthorpe
2020-09-14 20:52 ` Souptick Joarder
0 siblings, 1 reply; 7+ messages in thread
From: Jason Gunthorpe @ 2020-09-14 14:08 UTC (permalink / raw)
To: Souptick Joarder
Cc: Matthew Wilcox, Andrew Morton, Linux-MM, linux-kernel, John Hubbard
On Mon, Sep 14, 2020 at 07:20:34AM +0530, Souptick Joarder wrote:
> On Sun, Sep 13, 2020 at 8:25 PM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > On Sun, Sep 13, 2020 at 08:02:35PM +0530, Souptick Joarder wrote:
> > > It is possible that a buggy caller of unpin_user_pages()
> > > (specially in error handling path) may end up calling it with
> > > npages < 0 which is unnecessary.
> > > @@ -328,6 +328,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
> > > {
> > > unsigned long index;
> > >
> > > + if (WARN_ON_ONCE(npages < 0))
> > > + return;
> >
> > But npages is unsigned long. So it can't be less than zero.
>
> Sorry, I missed it.
>
> Then, it means if npages is assigned with -ERRNO by caller, unpin_user_pages()
> may end up calling a big loop, which is unnecessary.
How will a caller allocate memory of the right size and still manage
to call with the wrong npages? Do you have an example of a broken caller?
Jason
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm/gup.c: Handling ERR within unpin_user_pages()
2020-09-14 14:08 ` Jason Gunthorpe
@ 2020-09-14 20:52 ` Souptick Joarder
2020-09-14 20:56 ` John Hubbard
2020-09-14 21:01 ` Ira Weiny
0 siblings, 2 replies; 7+ messages in thread
From: Souptick Joarder @ 2020-09-14 20:52 UTC (permalink / raw)
To: Jason Gunthorpe
Cc: Matthew Wilcox, Andrew Morton, Linux-MM, linux-kernel, John Hubbard
On Mon, Sep 14, 2020 at 7:38 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
>
> On Mon, Sep 14, 2020 at 07:20:34AM +0530, Souptick Joarder wrote:
> > On Sun, Sep 13, 2020 at 8:25 PM Matthew Wilcox <willy@infradead.org> wrote:
> > >
> > > On Sun, Sep 13, 2020 at 08:02:35PM +0530, Souptick Joarder wrote:
> > > > It is possible that a buggy caller of unpin_user_pages()
> > > > (specially in error handling path) may end up calling it with
> > > > npages < 0 which is unnecessary.
> > > > @@ -328,6 +328,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
> > > > {
> > > > unsigned long index;
> > > >
> > > > + if (WARN_ON_ONCE(npages < 0))
> > > > + return;
> > >
> > > But npages is unsigned long. So it can't be less than zero.
> >
> > Sorry, I missed it.
> >
> > Then, it means if npages is assigned with -ERRNO by caller, unpin_user_pages()
> > may end up calling a big loop, which is unnecessary.
>
> How will a caller allocate memory of the right size and still manage
> to call with the wrong npages? Do you have an example of a broken caller?
These are two broken callers which might end up calling unpin_user_pages()
with -ERRNO.
drivers/rapidio/devices/rio_mport_cdev.c#L952
drivers/misc/mic/scif/scif_rma.c#L1399
They both are in error handling paths, so might not have any serious impact.
But theoretically possible.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm/gup.c: Handling ERR within unpin_user_pages()
2020-09-14 20:52 ` Souptick Joarder
@ 2020-09-14 20:56 ` John Hubbard
2020-09-14 21:01 ` Ira Weiny
1 sibling, 0 replies; 7+ messages in thread
From: John Hubbard @ 2020-09-14 20:56 UTC (permalink / raw)
To: Souptick Joarder, Jason Gunthorpe
Cc: Matthew Wilcox, Andrew Morton, Linux-MM, linux-kernel
On 9/14/20 1:52 PM, Souptick Joarder wrote:
> On Mon, Sep 14, 2020 at 7:38 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
>>
>> On Mon, Sep 14, 2020 at 07:20:34AM +0530, Souptick Joarder wrote:
>>> On Sun, Sep 13, 2020 at 8:25 PM Matthew Wilcox <willy@infradead.org> wrote:
>>>>
>>>> On Sun, Sep 13, 2020 at 08:02:35PM +0530, Souptick Joarder wrote:
>>>>> It is possible that a buggy caller of unpin_user_pages()
>>>>> (specially in error handling path) may end up calling it with
>>>>> npages < 0 which is unnecessary.
>>>>> @@ -328,6 +328,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
>>>>> {
>>>>> unsigned long index;
>>>>>
>>>>> + if (WARN_ON_ONCE(npages < 0))
>>>>> + return;
>>>>
>>>> But npages is unsigned long. So it can't be less than zero.
>>>
>>> Sorry, I missed it.
>>>
>>> Then, it means if npages is assigned with -ERRNO by caller, unpin_user_pages()
>>> may end up calling a big loop, which is unnecessary.
>>
>> How will a caller allocate memory of the right size and still manage
>> to call with the wrong npages? Do you have an example of a broken caller?
>
> These are two broken callers which might end up calling unpin_user_pages()
> with -ERRNO.
> drivers/rapidio/devices/rio_mport_cdev.c#L952
> drivers/misc/mic/scif/scif_rma.c#L1399
>
> They both are in error handling paths, so might not have any serious impact.
> But theoretically possible.
>
Eventually, I settled on fixing up the callers so that they match the gup/pup
API better. In other words, gup/pup has signed int for both input and return
value, and the callers need to handle that perfectly.
So let's fix up the callers.
thanks,
--
John Hubbard
NVIDIA
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm/gup.c: Handling ERR within unpin_user_pages()
2020-09-14 20:52 ` Souptick Joarder
2020-09-14 20:56 ` John Hubbard
@ 2020-09-14 21:01 ` Ira Weiny
1 sibling, 0 replies; 7+ messages in thread
From: Ira Weiny @ 2020-09-14 21:01 UTC (permalink / raw)
To: Souptick Joarder
Cc: Jason Gunthorpe, Matthew Wilcox, Andrew Morton, Linux-MM,
linux-kernel, John Hubbard
On Tue, Sep 15, 2020 at 02:22:33AM +0530, Souptick Joarder wrote:
> On Mon, Sep 14, 2020 at 7:38 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> >
> > On Mon, Sep 14, 2020 at 07:20:34AM +0530, Souptick Joarder wrote:
> > > On Sun, Sep 13, 2020 at 8:25 PM Matthew Wilcox <willy@infradead.org> wrote:
> > > >
> > > > On Sun, Sep 13, 2020 at 08:02:35PM +0530, Souptick Joarder wrote:
> > > > > It is possible that a buggy caller of unpin_user_pages()
> > > > > (specially in error handling path) may end up calling it with
> > > > > npages < 0 which is unnecessary.
> > > > > @@ -328,6 +328,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
> > > > > {
> > > > > unsigned long index;
> > > > >
> > > > > + if (WARN_ON_ONCE(npages < 0))
> > > > > + return;
> > > >
> > > > But npages is unsigned long. So it can't be less than zero.
> > >
> > > Sorry, I missed it.
> > >
> > > Then, it means if npages is assigned with -ERRNO by caller, unpin_user_pages()
> > > may end up calling a big loop, which is unnecessary.
> >
> > How will a caller allocate memory of the right size and still manage
> > to call with the wrong npages? Do you have an example of a broken caller?
>
> These are two broken callers which might end up calling unpin_user_pages()
> with -ERRNO.
> drivers/rapidio/devices/rio_mport_cdev.c#L952
The error here is that nr_pages should not be set to pinned if pinned is < 0.
Why not fix the logic there? Because it is inherently dangerous to set an
unsigned from a signed variable like that.
> drivers/misc/mic/scif/scif_rma.c#L1399
Again this is a caller who is not properly checking error conditions.
>
> They both are in error handling paths, so might not have any serious impact.
> But theoretically possible.
Actually I think they might have serious problems so they both should be fixed.
In the end this patch just can't work because npages can't be < 0 like Matthew
said.
Ira
^ permalink raw reply [flat|nested] 7+ messages in thread
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2020-09-13 14:32 [PATCH] mm/gup.c: Handling ERR within unpin_user_pages() Souptick Joarder
2020-09-13 14:55 ` Matthew Wilcox
2020-09-14 1:50 ` Souptick Joarder
2020-09-14 14:08 ` Jason Gunthorpe
2020-09-14 20:52 ` Souptick Joarder
2020-09-14 20:56 ` John Hubbard
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