Subject: [PATCH rdma-next 3/7] RDMA/mlx5: Avoid use after free in allocate MEMIC bad flow

From: Leon Romanovsky <[email-masked]>
Date: Thu, 18 Mar 2021 13:15:44 +0200

From: Maor Gottlieb <[email-masked]>

When driver fails to copy the MEMIC address to the user, we
call to rdma_user_mmap_entry_remove on the mmap entry. Since in this
state the refcount of the mmap entry is decreased to zero, mmap_free
is triggered and release the dm object. Therefore we need to avoid
the explicit call to free the dm.

Fixes: dc2316eba73f ("IB/mlx5: Fix device memory flows")
Signed-off-by: Maor Gottlieb <[email-masked]>
Signed-off-by: Leon Romanovsky <[email-masked]>
---
 drivers/infiniband/hw/mlx5/main.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
index 5226664f1bda..d652af720036 100644
--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -2375,13 +2375,18 @@ static int handle_alloc_dm_memic(struct ib_ucontext *ctx,

 	err = mlx5_cmd_alloc_memic(dm_db, &dm->dev_addr,
 				   dm->size, attr->alignment);
-	if (err)
+	if (err) {
+		kfree(dm);
 		return err;
+	}

 	address = dm->dev_addr & PAGE_MASK;
 	err = add_dm_mmap_entry(ctx, dm, address);
-	if (err)
-		goto err_dealloc;
+	if (err) {
+		mlx5_cmd_dealloc_memic(dm_db, dm->dev_addr, dm->size);
+		kfree(dm);
+		return err;
+	}

 	page_idx = dm->mentry.rdma_entry.start_pgoff & 0xFFFF;
 	err = uverbs_copy_to(attrs,
@@ -2402,8 +2407,6 @@ static int handle_alloc_dm_memic(struct ib_ucontext *ctx,

 err_copy:
 	rdma_user_mmap_entry_remove(&dm->mentry.rdma_entry);
-err_dealloc:
-	mlx5_cmd_dealloc_memic(dm_db, dm->dev_addr, dm->size);

 	return err;
 }
@@ -2472,9 +2475,7 @@ struct ib_dm *mlx5_ib_alloc_dm(struct ib_device *ibdev,

 	switch (type) {
 	case MLX5_IB_UAPI_DM_TYPE_MEMIC:
-		err = handle_alloc_dm_memic(context, dm,
-					    attr,
-					    attrs);
+		err = handle_alloc_dm_memic(context, dm, attr, attrs);
 		break;
 	case MLX5_IB_UAPI_DM_TYPE_STEERING_SW_ICM:
 		err = handle_alloc_dm_sw_icm(context, dm,
@@ -2496,7 +2497,9 @@ struct ib_dm *mlx5_ib_alloc_dm(struct ib_device *ibdev,
 	return &dm->ibdm;

 err_free:
-	kfree(dm);
+	/* In MEMIC error flow, dm will be freed internally */
+	if (type != MLX5_IB_UAPI_DM_TYPE_MEMIC)
+		kfree(dm);
 	return ERR_PTR(err);
 }

--
2.30.2