IB/uverbs: Fix locking around struct ib_uverbs_file ucontext

We have a parallel unlocked reader and writer with ib_uverbs_get_context()
vs everything else, and nothing guarantees this works properly.

Audit and fix all of the places that access ucontext to use one of the
following locking schemes:
- Call ib_uverbs_get_ucontext() under SRCU and check for failure
- Access the ucontext through an struct ib_uobject context member
  while holding a READ or WRITE lock on the uobject.
  This value cannot be NULL and has no race.
- Hold the ucontext_lock and check for ufile->ucontext !NULL

This also re-implements ib_uverbs_get_ucontext() in a way that is safe
against concurrent ib_uverbs_get_context() and disassociation.

As a side effect, every access to ucontext in the commands is via
ib_uverbs_get_context() with an error check, or via the uobject, so there
is no longer any need for the core code to check ucontext on every command
call. These checks are also removed.

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

1 files changed, 15 insertions, 5 deletions

diff --git a/drivers/infiniband/hw/mlx5/devx.c b/drivers/infiniband/hw/mlx5/devx.c
index 98b1575226c1..fee800f2fdec 100644
--- a/drivers/infiniband/hw/mlx5/devx.c
+++ b/drivers/infiniband/hw/mlx5/devx.c
@@ -458,16 +458,21 @@ static int UVERBS_HANDLER(MLX5_IB_METHOD_DEVX_QUERY_UAR)(struct ib_device *ib_de
 				  struct ib_uverbs_file *file,
 				  struct uverbs_attr_bundle *attrs)
 {
-	struct mlx5_ib_ucontext *c = devx_ufile2uctx(file);
+	struct mlx5_ib_ucontext *c;
+	struct mlx5_ib_dev *dev;
 	u32 user_idx;
 	s32 dev_idx;
 
+	c = devx_ufile2uctx(file);
+	if (IS_ERR(c))
+		return PTR_ERR(c);
+	dev = to_mdev(c->ibucontext.device);
+
 	if (uverbs_copy_from(&user_idx, attrs,
 			     MLX5_IB_ATTR_DEVX_QUERY_UAR_USER_IDX))
 		return -EFAULT;
 
-	dev_idx = bfregn_to_uar_index(to_mdev(ib_dev),
-				      &c->bfregi, user_idx, true);
+	dev_idx = bfregn_to_uar_index(dev, &c->bfregi, user_idx, true);
 	if (dev_idx < 0)
 		return dev_idx;
 
@@ -482,8 +487,8 @@ static int UVERBS_HANDLER(MLX5_IB_METHOD_DEVX_OTHER)(struct ib_device *ib_dev,
 				  struct ib_uverbs_file *file,
 				  struct uverbs_attr_bundle *attrs)
 {
-	struct mlx5_ib_ucontext *c = devx_ufile2uctx(file);
-	struct mlx5_ib_dev *dev = to_mdev(ib_dev);
+	struct mlx5_ib_ucontext *c;
+	struct mlx5_ib_dev *dev;
 	void *cmd_in = uverbs_attr_get_alloced_ptr(
 		attrs, MLX5_IB_ATTR_DEVX_OTHER_CMD_IN);
 	int cmd_out_len = uverbs_attr_get_len(attrs,
@@ -491,6 +496,11 @@ static int UVERBS_HANDLER(MLX5_IB_METHOD_DEVX_OTHER)(struct ib_device *ib_dev,
 	void *cmd_out;
 	int err;
 
+	c = devx_ufile2uctx(file);
+	if (IS_ERR(c))
+		return PTR_ERR(c);
+	dev = to_mdev(c->ibucontext.device);
+
 	if (!c->devx_uid)
 		return -EPERM;