| Message ID | 1594420826-4897-1-git-send-email-cohens@codeaurora.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm: hold gem reference until object is no longer accessed | expand |
Hi Steve and others. On Fri, Jul 10, 2020 at 06:40:26PM -0400, Steve Cohen wrote: > BUG: KASAN: use-after-free in drm_gem_open_ioctl > > There is potential for use-after-free here if the GEM object > handle is closed between the idr lookup and retrieving the size > from the object since a local reference is not being held at that > point. Hold the local reference while the object can still be > accessed to resolve this. > > Signed-off-by: Steve Cohen <cohens@codeaurora.org> > --- > drivers/gpu/drm/drm_gem.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c > index 7bf628e..4b2891c 100644 > --- a/drivers/gpu/drm/drm_gem.c > +++ b/drivers/gpu/drm/drm_gem.c > @@ -898,14 +898,15 @@ drm_gem_open_ioctl(struct drm_device *dev, void *data, > > /* drm_gem_handle_create_tail unlocks dev->object_name_lock. */ > ret = drm_gem_handle_create_tail(file_priv, obj, &handle); > - drm_gem_object_put_unlocked(obj); > if (ret) > - return ret; > + goto out; > > args->handle = handle; > args->size = obj->size; > > - return 0; > +out: > + drm_gem_object_put_unlocked(obj); > + return ret; Lookign at drm_gem_flink_ioctl() that is implmented just above this functions there are two things that I noted. 1) In drm_gem_flink_ioctl() the label is named "err:" - and my OCD likes that similar labels have the same name. 2) The function takes the object_name_lock but fails to release it in the error situation. Danile Vetter updated the locking in 20228c447846da9399ead53fdbbc8ab69b47788a ("drm/gem: completely close gem_open vs. gem_close races") but I failed to follow it all. Sam > } > > /** > -- > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, > a Linux Foundation Collaborative Project > > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel
Hi Steve. On Thu, Jul 16, 2020 at 10:29:52PM +0200, Sam Ravnborg wrote: > Hi Steve and others. > > On Fri, Jul 10, 2020 at 06:40:26PM -0400, Steve Cohen wrote: > > BUG: KASAN: use-after-free in drm_gem_open_ioctl > > > > There is potential for use-after-free here if the GEM object > > handle is closed between the idr lookup and retrieving the size > > from the object since a local reference is not being held at that > > point. Hold the local reference while the object can still be > > accessed to resolve this. > > > > Signed-off-by: Steve Cohen <cohens@codeaurora.org> > > --- > > drivers/gpu/drm/drm_gem.c | 7 ++++--- > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c > > index 7bf628e..4b2891c 100644 > > --- a/drivers/gpu/drm/drm_gem.c > > +++ b/drivers/gpu/drm/drm_gem.c > > @@ -898,14 +898,15 @@ drm_gem_open_ioctl(struct drm_device *dev, void *data, > > > > /* drm_gem_handle_create_tail unlocks dev->object_name_lock. */ > > ret = drm_gem_handle_create_tail(file_priv, obj, &handle); > > - drm_gem_object_put_unlocked(obj); > > if (ret) > > - return ret; > > + goto out; > > > > args->handle = handle; > > args->size = obj->size; > > > > - return 0; > > +out: > > + drm_gem_object_put_unlocked(obj); > > + return ret; > > Lookign at drm_gem_flink_ioctl() that is implmented just above this > functions there are two things that I noted. > > 1) In drm_gem_flink_ioctl() the label is named "err:" - and my OCD likes > that similar labels have the same name. > > 2) The function takes the object_name_lock but fails to release it in > the error situation. Daniel pointed out on irc that drm_gem_handle_create_tail releases the lock. If I had read the comment I would have noticed too - sigh. With the label name fixed to "err:" like used in the function above: Reviewed-by: Sam Ravnborg <sam@ravnborg.org> Please re-submit. Sam > > Danile Vetter updated the locking in > 20228c447846da9399ead53fdbbc8ab69b47788a ("drm/gem: completely close gem_open vs. gem_close races") > > but I failed to follow it all. > > Sam > > > } > > > > /** > > -- > > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, > > a Linux Foundation Collaborative Project > > > > _______________________________________________ > > dri-devel mailing list > > dri-devel@lists.freedesktop.org > > https://lists.freedesktop.org/mailman/listinfo/dri-devel > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel
diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c index 7bf628e..4b2891c 100644 --- a/drivers/gpu/drm/drm_gem.c +++ b/drivers/gpu/drm/drm_gem.c @@ -898,14 +898,15 @@ drm_gem_open_ioctl(struct drm_device *dev, void *data, /* drm_gem_handle_create_tail unlocks dev->object_name_lock. */ ret = drm_gem_handle_create_tail(file_priv, obj, &handle); - drm_gem_object_put_unlocked(obj); if (ret) - return ret; + goto out; args->handle = handle; args->size = obj->size; - return 0; +out: + drm_gem_object_put_unlocked(obj); + return ret; } /**
BUG: KASAN: use-after-free in drm_gem_open_ioctl There is potential for use-after-free here if the GEM object handle is closed between the idr lookup and retrieving the size from the object since a local reference is not being held at that point. Hold the local reference while the object can still be accessed to resolve this. Signed-off-by: Steve Cohen <cohens@codeaurora.org> --- drivers/gpu/drm/drm_gem.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)