2021-10-12 13:27:46

by Colin King

Subject: [PATCH][next] drm/i915: Fix dereference of pointer backup before it is null checked

From: Colin Ian King <[email protected]>

The assignment of pointer backup_bo dereferences pointer backup before
backup is null checked, this could lead to a null pointer dereference
issue. Fix this by only assigning backup_bo after backup has been null
checked.

Addresses-Coverity: ("Dereference before null check")
Fixes: c56ce9565374 ("drm/i915 Implement LMEM backup and restore for suspend / resume")
Signed-off-by: Colin Ian King <[email protected]>
---
drivers/gpu/drm/i915/gem/i915_gem_ttm_pm.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm_pm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm_pm.c
index 3b6d14b5c604..4ec6c557083a 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_ttm_pm.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm_pm.c
@@ -149,7 +149,7 @@ static int i915_ttm_restore(struct i915_gem_apply_to_region *apply,
struct i915_gem_ttm_pm_apply *pm_apply =
container_of(apply, typeof(*pm_apply), base);
struct drm_i915_gem_object *backup = obj->ttm.backup;
- struct ttm_buffer_object *backup_bo = i915_gem_to_ttm(backup);
+ struct ttm_buffer_object *backup_bo;
struct ttm_operation_ctx ctx = {};
int err;

@@ -163,6 +163,8 @@ static int i915_ttm_restore(struct i915_gem_apply_to_region *apply,
if (err)
return err;

+ backup_bo = i915_gem_to_ttm(backup);
+
/* Content may have been swapped. */
err = ttm_tt_populate(backup_bo->bdev, backup_bo->ttm, &ctx);
if (!err) {
--
2.32.0

2021-10-12 14:49:49

by Thomas Hellström

Subject: Re: [PATCH][next] drm/i915: Fix dereference of pointer backup before it is null checked

Hi,

On 10/12/21 15:25, Colin King wrote:
> From: Colin Ian King <[email protected]>
>
> The assignment of pointer backup_bo dereferences pointer backup before
> backup is null checked, this could lead to a null pointer dereference
> issue. Fix this by only assigning backup_bo after backup has been null
> checked.
>
> Addresses-Coverity: ("Dereference before null check")
> Fixes: c56ce9565374 ("drm/i915 Implement LMEM backup and restore for suspend / resume")
> Signed-off-by: Colin Ian King <[email protected]>

There's not really a pointer dereference here, just pointer arithmetics,
so the code should be safe (but admittedly fragile), so to keep Coverity
happy,

Reviewed-by: Thomas Hellström <[email protected]>



> ---
> drivers/gpu/drm/i915/gem/i915_gem_ttm_pm.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm_pm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm_pm.c
> index 3b6d14b5c604..4ec6c557083a 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm_pm.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm_pm.c
> @@ -149,7 +149,7 @@ static int i915_ttm_restore(struct i915_gem_apply_to_region *apply,
> struct i915_gem_ttm_pm_apply *pm_apply =
> container_of(apply, typeof(*pm_apply), base);
> struct drm_i915_gem_object *backup = obj->ttm.backup;
> - struct ttm_buffer_object *backup_bo = i915_gem_to_ttm(backup);
> + struct ttm_buffer_object *backup_bo;
> struct ttm_operation_ctx ctx = {};
> int err;
>
> @@ -163,6 +163,8 @@ static int i915_ttm_restore(struct i915_gem_apply_to_region *apply,
> if (err)
> return err;
>
> + backup_bo = i915_gem_to_ttm(backup);
> +
> /* Content may have been swapped. */
> err = ttm_tt_populate(backup_bo->bdev, backup_bo->ttm, &ctx);
> if (!err) {

2021-10-12 15:15:00

by Dan Carpenter

Subject: Re: [PATCH][next] drm/i915: Fix dereference of pointer backup before it is null checked

On Tue, Oct 12, 2021 at 04:47:24PM +0200, Thomas Hellstr?m wrote:
> Hi,
>
> On 10/12/21 15:25, Colin King wrote:
> > From: Colin Ian King <[email protected]>
> >
> > The assignment of pointer backup_bo dereferences pointer backup before
> > backup is null checked, this could lead to a null pointer dereference
> > issue. Fix this by only assigning backup_bo after backup has been null
> > checked.
> >
> > Addresses-Coverity: ("Dereference before null check")
> > Fixes: c56ce9565374 ("drm/i915 Implement LMEM backup and restore for suspend / resume")
> > Signed-off-by: Colin Ian King <[email protected]>
>
> There's not really a pointer dereference here, just pointer arithmetics, so
> the code should be safe (but admittedly fragile), so to keep Coverity happy,
>
> Reviewed-by: Thomas Hellstr?m <[email protected]>

Yeah. I kind of feel like we shouldn't work around static checker bugs.
But when we do then there shouldn't be a Fixes tag.

regards,
dan carpenter