[PATCH v2 2/2] drm: Protect drm_master pointers in drm_lease.c

From: Desmond Cheong Zhi Xi
Date: Mon Jun 14 2021 - 22:49:15 EST

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This patch ensures that the device's master mutex is acquired before
accessing pointers to struct drm_master that are subsequently
dereferenced. Without the mutex, the struct drm_master may be freed
concurrently by another process calling drm_setmaster_ioctl(). This
could then lead to use-after-free errors.

Reported-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx>
Reviewed-by: Emil Velikov <emil.l.velikov@xxxxxxxxx>
---
drivers/gpu/drm/drm_lease.c | 58 +++++++++++++++++++++++++++----------
1 file changed, 43 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/drm_lease.c b/drivers/gpu/drm/drm_lease.c
index da4f085fc09e..3e6f689236e5 100644
--- a/drivers/gpu/drm/drm_lease.c
+++ b/drivers/gpu/drm/drm_lease.c
@@ -107,10 +107,16 @@ static bool _drm_has_leased(struct drm_master *master, int id)
*/
bool _drm_lease_held(struct drm_file *file_priv, int id)
{
+ bool ret;
+
if (!file_priv || !file_priv->master)
return true;

- return _drm_lease_held_master(file_priv->master, id);
+ mutex_lock(&file_priv->master->dev->master_mutex);
+ ret = _drm_lease_held_master(file_priv->master, id);
+ mutex_unlock(&file_priv->master->dev->master_mutex);
+
+ return ret;
}

/**
@@ -132,10 +138,12 @@ bool drm_lease_held(struct drm_file *file_priv, int id)
if (!file_priv || !file_priv->master || !file_priv->master->lessor)
return true;

+ mutex_lock(&file_priv->master->dev->master_mutex);
master = file_priv->master;
mutex_lock(&master->dev->mode_config.idr_mutex);
ret = _drm_lease_held_master(master, id);
mutex_unlock(&master->dev->mode_config.idr_mutex);
+ mutex_unlock(&file_priv->master->dev->master_mutex);
return ret;
}

@@ -158,6 +166,7 @@ uint32_t drm_lease_filter_crtcs(struct drm_file *file_priv, uint32_t crtcs_in)
if (!file_priv || !file_priv->master || !file_priv->master->lessor)
return crtcs_in;

+ mutex_lock(&file_priv->master->dev->master_mutex);
master = file_priv->master;
dev = master->dev;

@@ -177,6 +186,7 @@ uint32_t drm_lease_filter_crtcs(struct drm_file *file_priv, uint32_t crtcs_in)
count_in++;
}
mutex_unlock(&master->dev->mode_config.idr_mutex);
+ mutex_unlock(&file_priv->master->dev->master_mutex);
return crtcs_out;
}

@@ -490,7 +500,7 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev,
size_t object_count;
int ret = 0;
struct idr leases;
- struct drm_master *lessor = lessor_priv->master;
+ struct drm_master *lessor;
struct drm_master *lessee = NULL;
struct file *lessee_file = NULL;
struct file *lessor_file = lessor_priv->filp;
@@ -502,12 +512,6 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev,
if (!drm_core_check_feature(dev, DRIVER_MODESET))
return -EOPNOTSUPP;

- /* Do not allow sub-leases */
- if (lessor->lessor) {
- DRM_DEBUG_LEASE("recursive leasing not allowed\n");
- return -EINVAL;
- }
-
/* need some objects */
if (cl->object_count == 0) {
DRM_DEBUG_LEASE("no objects in lease\n");
@@ -519,12 +523,23 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev,
return -EINVAL;
}

+ mutex_lock(&dev->master_mutex);
+ lessor = lessor_priv->master;
+ /* Do not allow sub-leases */
+ if (lessor->lessor) {
+ DRM_DEBUG_LEASE("recursive leasing not allowed\n");
+ ret = -EINVAL;
+ goto unlock;
+ }
+
object_count = cl->object_count;

object_ids = memdup_user(u64_to_user_ptr(cl->object_ids),
array_size(object_count, sizeof(__u32)));
- if (IS_ERR(object_ids))
- return PTR_ERR(object_ids);
+ if (IS_ERR(object_ids)) {
+ ret = PTR_ERR(object_ids);
+ goto unlock;
+ }

idr_init(&leases);

@@ -535,14 +550,15 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev,
if (ret) {
DRM_DEBUG_LEASE("lease object lookup failed: %i\n", ret);
idr_destroy(&leases);
- return ret;
+ goto unlock;
}

/* Allocate a file descriptor for the lease */
fd = get_unused_fd_flags(cl->flags & (O_CLOEXEC | O_NONBLOCK));
if (fd < 0) {
idr_destroy(&leases);
- return fd;
+ ret = fd;
+ goto unlock;
}

DRM_DEBUG_LEASE("Creating lease\n");
@@ -578,6 +594,7 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev,
/* Hook up the fd */
fd_install(fd, lessee_file);

+ mutex_unlock(&dev->master_mutex);
DRM_DEBUG_LEASE("drm_mode_create_lease_ioctl succeeded\n");
return 0;

@@ -587,6 +604,8 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev,
out_leases:
put_unused_fd(fd);

+unlock:
+ mutex_unlock(&dev->master_mutex);
DRM_DEBUG_LEASE("drm_mode_create_lease_ioctl failed: %d\n", ret);
return ret;
}
@@ -609,7 +628,7 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev,
struct drm_mode_list_lessees *arg = data;
__u32 __user *lessee_ids = (__u32 __user *) (uintptr_t) (arg->lessees_ptr);
__u32 count_lessees = arg->count_lessees;
- struct drm_master *lessor = lessor_priv->master, *lessee;
+ struct drm_master *lessor, *lessee;
int count;
int ret = 0;

@@ -620,6 +639,8 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev,
if (!drm_core_check_feature(dev, DRIVER_MODESET))
return -EOPNOTSUPP;

+ mutex_lock(&dev->master_mutex);
+ lessor = lessor_priv->master;
DRM_DEBUG_LEASE("List lessees for %d\n", lessor->lessee_id);

mutex_lock(&dev->mode_config.idr_mutex);
@@ -643,6 +664,7 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev,
arg->count_lessees = count;

mutex_unlock(&dev->mode_config.idr_mutex);
+ mutex_unlock(&dev->master_mutex);

return ret;
}
@@ -662,7 +684,7 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev,
struct drm_mode_get_lease *arg = data;
__u32 __user *object_ids = (__u32 __user *) (uintptr_t) (arg->objects_ptr);
__u32 count_objects = arg->count_objects;
- struct drm_master *lessee = lessee_priv->master;
+ struct drm_master *lessee;
struct idr *object_idr;
int count;
void *entry;
@@ -676,6 +698,8 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev,
if (!drm_core_check_feature(dev, DRIVER_MODESET))
return -EOPNOTSUPP;

+ mutex_lock(&dev->master_mutex);
+ lessee = lessee_priv->master;
DRM_DEBUG_LEASE("get lease for %d\n", lessee->lessee_id);

mutex_lock(&dev->mode_config.idr_mutex);
@@ -703,6 +727,7 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev,
arg->count_objects = count;

mutex_unlock(&dev->mode_config.idr_mutex);
+ mutex_unlock(&dev->master_mutex);

return ret;
}
@@ -721,7 +746,7 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev,
void *data, struct drm_file *lessor_priv)
{
struct drm_mode_revoke_lease *arg = data;
- struct drm_master *lessor = lessor_priv->master;
+ struct drm_master *lessor;
struct drm_master *lessee;
int ret = 0;

@@ -731,8 +756,10 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev,
if (!drm_core_check_feature(dev, DRIVER_MODESET))
return -EOPNOTSUPP;

+ mutex_lock(&dev->master_mutex);
mutex_lock(&dev->mode_config.idr_mutex);

+ lessor = lessor_priv->master;
lessee = _drm_find_lessee(lessor, arg->lessee_id);

/* No such lessee */
@@ -751,6 +778,7 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev,

fail:
mutex_unlock(&dev->mode_config.idr_mutex);
+ mutex_unlock(&dev->master_mutex);

return ret;
}
--
2.25.1

Next message: Daniel Axtens: "[PATCH v12 0/6] KASAN core changes for ppc64 radix KASAN"
Previous message: Desmond Cheong Zhi Xi: "[PATCH v2 1/2] drm: Add a locked version of drm_is_current_master"
In reply to: Desmond Cheong Zhi Xi: "[PATCH v2 1/2] drm: Add a locked version of drm_is_current_master"
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