* [PATCH] amd64-agp: fix arbitrary kernel memory writes
@ 2019-05-29 4:52 Young Xiao
2019-05-29 8:34 ` Greg KH
0 siblings, 1 reply; 3+ messages in thread
From: Young Xiao @ 2019-05-29 4:52 UTC (permalink / raw)
To: airlied, arnd, gregkh, linux-kernel; +Cc: Young Xiao
pg_start is copied from userspace on AGPIOC_BIND and AGPIOC_UNBIND ioctl
cmds of agp_ioctl() and passed to agpioc_bind_wrap(). As said in the
comment, (pg_start + mem->page_count) may wrap in case of AGPIOC_BIND,
and it is not checked at all in case of AGPIOC_UNBIND. As a result, user
with sufficient privileges (usually "video" group) may generate either
local DoS or privilege escalation.
See commit 194b3da873fd ("agp: fix arbitrary kernel memory writes")
for details.
Signed-off-by: Young Xiao <92siuyang@gmail.com>
---
drivers/char/agp/amd64-agp.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/char/agp/amd64-agp.c b/drivers/char/agp/amd64-agp.c
index c69e39f..5daa0e3 100644
--- a/drivers/char/agp/amd64-agp.c
+++ b/drivers/char/agp/amd64-agp.c
@@ -60,7 +60,8 @@ static int amd64_insert_memory(struct agp_memory *mem, off_t pg_start, int type)
/* Make sure we can fit the range in the gatt table. */
/* FIXME: could wrap */
- if (((unsigned long)pg_start + mem->page_count) > num_entries)
+ if (((pg_start + mem->page_count) > num_entries) ||
+ ((pg_start + mem->page_count) < pg_start))
return -EINVAL;
j = pg_start;
--
2.7.4
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] amd64-agp: fix arbitrary kernel memory writes
2019-05-29 4:52 [PATCH] amd64-agp: fix arbitrary kernel memory writes Young Xiao
@ 2019-05-29 8:34 ` Greg KH
2019-05-29 15:14 ` Yang Xiao
0 siblings, 1 reply; 3+ messages in thread
From: Greg KH @ 2019-05-29 8:34 UTC (permalink / raw)
To: Young Xiao; +Cc: airlied, arnd, linux-kernel
On Wed, May 29, 2019 at 12:52:01PM +0800, Young Xiao wrote:
> pg_start is copied from userspace on AGPIOC_BIND and AGPIOC_UNBIND ioctl
> cmds of agp_ioctl() and passed to agpioc_bind_wrap(). As said in the
> comment, (pg_start + mem->page_count) may wrap in case of AGPIOC_BIND,
> and it is not checked at all in case of AGPIOC_UNBIND. As a result, user
> with sufficient privileges (usually "video" group) may generate either
> local DoS or privilege escalation.
>
> See commit 194b3da873fd ("agp: fix arbitrary kernel memory writes")
> for details.
>
> Signed-off-by: Young Xiao <92siuyang@gmail.com>
> ---
> drivers/char/agp/amd64-agp.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/char/agp/amd64-agp.c b/drivers/char/agp/amd64-agp.c
> index c69e39f..5daa0e3 100644
> --- a/drivers/char/agp/amd64-agp.c
> +++ b/drivers/char/agp/amd64-agp.c
> @@ -60,7 +60,8 @@ static int amd64_insert_memory(struct agp_memory *mem, off_t pg_start, int type)
>
> /* Make sure we can fit the range in the gatt table. */
> /* FIXME: could wrap */
> - if (((unsigned long)pg_start + mem->page_count) > num_entries)
> + if (((pg_start + mem->page_count) > num_entries) ||
> + ((pg_start + mem->page_count) < pg_start))
Why did you take off the cast for the first test?
And if this really does fix this issue, should you remove the FIXME
line?
thanks,
greg k-h
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] amd64-agp: fix arbitrary kernel memory writes
2019-05-29 8:34 ` Greg KH
@ 2019-05-29 15:14 ` Yang Xiao
0 siblings, 0 replies; 3+ messages in thread
From: Yang Xiao @ 2019-05-29 15:14 UTC (permalink / raw)
To: Greg KH; +Cc: airlied, arnd, LKML
I am not so sure about taking off the cast, just to be in line with
patch in 194b3da873fd.
The comment can be deleted.
On Wed, May 29, 2019 at 4:35 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Wed, May 29, 2019 at 12:52:01PM +0800, Young Xiao wrote:
> > pg_start is copied from userspace on AGPIOC_BIND and AGPIOC_UNBIND ioctl
> > cmds of agp_ioctl() and passed to agpioc_bind_wrap(). As said in the
> > comment, (pg_start + mem->page_count) may wrap in case of AGPIOC_BIND,
> > and it is not checked at all in case of AGPIOC_UNBIND. As a result, user
> > with sufficient privileges (usually "video" group) may generate either
> > local DoS or privilege escalation.
> >
> > See commit 194b3da873fd ("agp: fix arbitrary kernel memory writes")
> > for details.
> >
> > Signed-off-by: Young Xiao <92siuyang@gmail.com>
> > ---
> > drivers/char/agp/amd64-agp.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/char/agp/amd64-agp.c b/drivers/char/agp/amd64-agp.c
> > index c69e39f..5daa0e3 100644
> > --- a/drivers/char/agp/amd64-agp.c
> > +++ b/drivers/char/agp/amd64-agp.c
> > @@ -60,7 +60,8 @@ static int amd64_insert_memory(struct agp_memory *mem, off_t pg_start, int type)
> >
> > /* Make sure we can fit the range in the gatt table. */
> > /* FIXME: could wrap */
> > - if (((unsigned long)pg_start + mem->page_count) > num_entries)
> > + if (((pg_start + mem->page_count) > num_entries) ||
> > + ((pg_start + mem->page_count) < pg_start))
>
> Why did you take off the cast for the first test?
>
> And if this really does fix this issue, should you remove the FIXME
> line?
>
> thanks,
>
> greg k-h
--
Best regards!
Young
-----------------------------------------------------------
^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-05-29 4:52 [PATCH] amd64-agp: fix arbitrary kernel memory writes Young Xiao
2019-05-29 8:34 ` Greg KH
2019-05-29 15:14 ` Yang Xiao
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