RDMA/ucm: Mark UCM interface as BROKEN

In commit 357d23c811a7 ("Remove the obsolete libibcm library")
in rdma-core [1], we removed obsolete library which used the
/dev/infiniband/ucmX interface.

Following multiple syzkaller reports about non-sanitized
user input in the UCMA module, the short audit reveals the same
issues in UCM module too.

It is better to disable this interface in the kernel,
before syzkaller team invests time and energy to harden
this unused interface.

[1] linux-rdma/rdma-core#279

Signed-off-by: Leon Romanovsky <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>

Author: Leon Romanovsky

drivers/infiniband/Kconfig

@@ -35,6 +35,17 @@ config INFINIBAND_USER_ACCESS
 	  libibverbs, libibcm and a hardware driver library from
 	  rdma-core <https://github.com/linux-rdma/rdma-core>.
 
+config INFINIBAND_USER_ACCESS_UCM
+	bool "Userspace CM (UCM, DEPRECATED)"
+	depends on BROKEN
+	depends on INFINIBAND_USER_ACCESS
+	help
+	  The UCM module has known security flaws, which no one is
+	  interested to fix. The user-space part of this code was
+	  dropped from the upstream a long time ago.
+
+	  This option is DEPRECATED and planned to be removed.
+
 config INFINIBAND_EXP_LEGACY_VERBS_NEW_UAPI
 	bool "Allow experimental legacy verbs in new ioctl uAPI  (EXPERIMENTAL)"
 	depends on INFINIBAND_USER_ACCESS

drivers/infiniband/core/Makefile

@@ -5,8 +5,8 @@ user_access-$(CONFIG_INFINIBAND_ADDR_TRANS)	:= rdma_ucm.o
 obj-$(CONFIG_INFINIBAND) +=		ib_core.o ib_cm.o iw_cm.o \
 					$(infiniband-y)
 obj-$(CONFIG_INFINIBAND_USER_MAD) +=	ib_umad.o
-obj-$(CONFIG_INFINIBAND_USER_ACCESS) +=	ib_uverbs.o ib_ucm.o \
-					$(user_access-y)
+obj-$(CONFIG_INFINIBAND_USER_ACCESS) += ib_uverbs.o $(user_access-y)
+obj-$(CONFIG_INFINIBAND_USER_ACCESS_UCM) += ib_ucm.o $(user_access-y)
 
 ib_core-y :=			packer.o ud_header.o verbs.o cq.o rw.o sysfs.o \
 				device.o fmr_pool.o cache.o netlink.o \