2022-06-28 06:31:13

by Yu Liao

[permalink] [raw]
Subject: [PATCH] drm/vc4: fix dereference before NULL check

The "perfmon" pointer is equal to the return value of idr_find
which may be NULL, access by vc4_perfmon_get before checking if
it was NULL. Fix this by dereferencing "perfmon" after "perfmon"
has been null checked.

Addresses-Coverity: ("Dereference before null check")
Fixes: 65101d8c9108 ("drm/vc4: Expose performance counters to userspace")
Signed-off-by: Yu Liao <[email protected]>
---
drivers/gpu/drm/vc4/vc4_perfmon.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_perfmon.c b/drivers/gpu/drm/vc4/vc4_perfmon.c
index c7f5adb6bcf8..ca969b8c7dde 100644
--- a/drivers/gpu/drm/vc4/vc4_perfmon.c
+++ b/drivers/gpu/drm/vc4/vc4_perfmon.c
@@ -17,13 +17,17 @@

void vc4_perfmon_get(struct vc4_perfmon *perfmon)
{
- struct vc4_dev *vc4 = perfmon->dev;
+ struct vc4_dev *vc4;
+
+ if (!perfmon)
+ return;
+
+ vc4 = perfmon->dev;

if (WARN_ON_ONCE(vc4->is_vc5))
return;

- if (perfmon)
- refcount_inc(&perfmon->refcnt);
+ refcount_inc(&perfmon->refcnt);
}

void vc4_perfmon_put(struct vc4_perfmon *perfmon)
--
2.25.1


2022-06-28 07:31:55

by Boris Brezillon

[permalink] [raw]
Subject: Re: [PATCH] drm/vc4: fix dereference before NULL check

On Tue, 28 Jun 2022 14:36:57 +0800
Yu Liao <[email protected]> wrote:

> The "perfmon" pointer is equal to the return value of idr_find
> which may be NULL, access by vc4_perfmon_get before checking if
> it was NULL. Fix this by dereferencing "perfmon" after "perfmon"
> has been null checked.
>
> Addresses-Coverity: ("Dereference before null check")
> Fixes: 65101d8c9108 ("drm/vc4: Expose performance counters to userspace")
> Signed-off-by: Yu Liao <[email protected]>

Reviewed-by: Boris Brezillon <[email protected]>

> ---
> drivers/gpu/drm/vc4/vc4_perfmon.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_perfmon.c b/drivers/gpu/drm/vc4/vc4_perfmon.c
> index c7f5adb6bcf8..ca969b8c7dde 100644
> --- a/drivers/gpu/drm/vc4/vc4_perfmon.c
> +++ b/drivers/gpu/drm/vc4/vc4_perfmon.c
> @@ -17,13 +17,17 @@
>
> void vc4_perfmon_get(struct vc4_perfmon *perfmon)
> {
> - struct vc4_dev *vc4 = perfmon->dev;
> + struct vc4_dev *vc4;
> +
> + if (!perfmon)
> + return;
> +
> + vc4 = perfmon->dev;
>
> if (WARN_ON_ONCE(vc4->is_vc5))
> return;
>
> - if (perfmon)
> - refcount_inc(&perfmon->refcnt);
> + refcount_inc(&perfmon->refcnt);
> }
>
> void vc4_perfmon_put(struct vc4_perfmon *perfmon)

2022-06-28 08:29:07

by Maxime Ripard

[permalink] [raw]
Subject: Re: [PATCH] drm/vc4: fix dereference before NULL check

Hi,

On Tue, Jun 28, 2022 at 02:36:57PM +0800, Yu Liao wrote:
> The "perfmon" pointer is equal to the return value of idr_find
> which may be NULL, access by vc4_perfmon_get before checking if
> it was NULL. Fix this by dereferencing "perfmon" after "perfmon"
> has been null checked.
>
> Addresses-Coverity: ("Dereference before null check")
> Fixes: 65101d8c9108 ("drm/vc4: Expose performance counters to userspace")
> Signed-off-by: Yu Liao <[email protected]>

A similar patch has already been merged:
https://lore.kernel.org/dri-devel/[email protected]/

Thanks!
Maxime

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