CVE-2021-47615

In the Linux kernel, the following vulnerability has been resolved:

RDMA/mlx5: Fix releasing unallocated memory in dereg MR flow

For the case of IB_MR_TYPE_DM the mr does doesn’t have a umem, even though
it is a user MR. This causes function mlx5_free_priv_descs() to think that
it is a kernel MR, leading to wrongly accessing mr->descs that will get
wrong values in the union which leads to attempt to release resources that
were not allocated in the first place.

For example:
DMA-API: mlx5_core 0000:08:00.1: device driver tries to free DMA memory it has not allocated [device address=0x0000000000000000] [size=0 bytes]
WARNING: CPU: 8 PID: 1021 at kernel/dma/debug.c:961 check_unmap+0x54f/0x8b0
RIP: 0010:check_unmap+0x54f/0x8b0
Call Trace:
debug_dma_unmap_page+0x57/0x60
mlx5_free_priv_descs+0x57/0x70 [mlx5_ib]
mlx5_ib_dereg_mr+0x1fb/0x3d0 [mlx5_ib]
ib_dereg_mr_user+0x60/0x140 [ib_core]
uverbs_destroy_uobject+0x59/0x210 [ib_uverbs]
uobj_destroy+0x3f/0x80 [ib_uverbs]
ib_uverbs_cmd_verbs+0x435/0xd10 [ib_uverbs]
? uverbs_finalize_object+0x50/0x50 [ib_uverbs]
? lock_acquire+0xc4/0x2e0
? lock_acquired+0x12/0x380
? lock_acquire+0xc4/0x2e0
? lock_acquire+0xc4/0x2e0
? ib_uverbs_ioctl+0x7c/0x140 [ib_uverbs]
? lock_release+0x28a/0x400
ib_uverbs_ioctl+0xc0/0x140 [ib_uverbs]
? ib_uverbs_ioctl+0x7c/0x140 [ib_uverbs]
__x64_sys_ioctl+0x7f/0xb0
do_syscall_64+0x38/0x90

Fix it by reorganizing the dereg flow and mlx5_ib_mr structure:

• Move the ib_umem field into the user MRs structure in the union as it’s
  applicable only there.
• Function mlx5_ib_dereg_mr() will now call mlx5_free_priv_descs() only
  in case there isn’t udata, which indicates that this isn’t a user MR.