[PATCH] IB/security: Restrict use of the write() interface

Doug Ledford
2016-05-18T16:58:38Z

From: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>

The drivers/infiniband stack uses write() as a replacement for
bi-directional ioctl(). This is not safe. There are ways to
trigger write calls that result in the return structure that
is normally written to user space being shunted off to user
specified kernel memory instead.

For the immediate repair, detect and deny suspicious accesses to
the write API.

For long term, update the user space libraries and the kernel API
to something that doesn't present the same security vulnerabilities
(likely a structured ioctl() interface).

The impacted uAPI interfaces are generally only available if
hardware from drivers/infiniband is installed in the system.

Reported-by: Jann Horn <jann@thejh.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
[ Expanded check to all known write() entry points ]
Cc: stable@vger.kernel.org # 3.14.x
Signed-off-by: Doug Ledford <dledford@redhat.com>
[ Expanded to include removed ipath driver, and dropped non-existent
hfi1 driver ]
---
drivers/infiniband/core/ucm.c | 4 ++++
drivers/infiniband/core/ucma.c | 3 +++
drivers/infiniband/core/uverbs_main.c | 5 +++++
drivers/infiniband/hw/ipath/ipath_file_ops.c | 5 +++++
drivers/infiniband/hw/qib/qib_file_ops.c | 5 +++++
include/rdma/ib.h | 16 ++++++++++++++++
6 files changed, 38 insertions(+)

diff --git a/drivers/infiniband/core/ucm.c b/drivers/infiniband/core/ucm.c
index f2f63933e8a9..5befec118a18 100644
--- a/drivers/infiniband/core/ucm.c
+++ b/drivers/infiniband/core/ucm.c
@@ -48,6 +48,7 @@

#include <asm/uaccess.h>

+#include <rdma/ib.h>
#include <rdma/ib_cm.h>
#include <rdma/ib_user_cm.h>
#include <rdma/ib_marshall.h>
@@ -1104,6 +1105,9 @@ static ssize_t ib_ucm_write(struct file *filp, const char __user *buf,
struct ib_ucm_cmd_hdr hdr;
ssize_t result;

+ if (WARN_ON_ONCE(!ib_safe_file_access(filp)))
+ return -EACCES;
+
if (len < sizeof(hdr))
return -EINVAL;

diff --git a/drivers/infiniband/core/ucma.c b/drivers/infiniband/core/ucma.c
index 56a4b7ca7ee3..22e02805147b 100644
--- a/drivers/infiniband/core/ucma.c
+++ b/drivers/infiniband/core/ucma.c
@@ -1484,6 +1484,9 @@ static ssize_t ucma_write(struct file *filp, const char __user *buf,
struct rdma_ucm_cmd_hdr hdr;
ssize_t ret;

+ if (WARN_ON_ONCE(!ib_safe_file_access(filp)))
+ return -EACCES;
+
if (len < sizeof(hdr))
return -EINVAL;

diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
index 08219fb3338b..d12ae04657c8 100644
--- a/drivers/infiniband/core/uverbs_main.c
+++ b/drivers/infiniband/core/uverbs_main.c
@@ -48,6 +48,8 @@

#include <asm/uaccess.h>

+#include <rdma/ib.h>
+
#include "uverbs.h"

MODULE_AUTHOR("Roland Dreier");
@@ -594,6 +596,9 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
struct ib_uverbs_cmd_hdr hdr;
__u32 flags;

+ if (WARN_ON_ONCE(!ib_safe_file_access(filp)))
+ return -EACCES;
+
if (count < sizeof hdr)
return -EINVAL;

diff --git a/drivers/infiniband/hw/ipath/ipath_file_ops.c b/drivers/infiniband/hw/ipath/ipath_file_ops.c
index 6d7f453b4d05..2b828ea3ac4a 100644
--- a/drivers/infiniband/hw/ipath/ipath_file_ops.c
+++ b/drivers/infiniband/hw/ipath/ipath_file_ops.c
@@ -45,6 +45,8 @@
#include <linux/cpu.h>
#include <asm/pgtable.h>

+#include "rdma/ib.h"
+
#include "ipath_kernel.h"
#include "ipath_common.h"
#include "ipath_user_sdma.h"
@@ -2240,6 +2242,9 @@ static ssize_t ipath_write(struct file *fp, const char __user *data,
ssize_t ret = 0;
void *dest;

+ if (WARN_ON_ONCE(!ib_safe_file_access(filp)))
+ return -EACCES;
+
if (count < sizeof(cmd.type)) {
ret = -EINVAL;
goto bail;
diff --git a/drivers/infiniband/hw/qib/qib_file_ops.c b/drivers/infiniband/hw/qib/qib_file_ops.c
index 275f247f9fca..ff5e7acc8d3f 100644
--- a/drivers/infiniband/hw/qib/qib_file_ops.c
+++ b/drivers/infiniband/hw/qib/qib_file_ops.c
@@ -45,6 +45,8 @@
#include <linux/delay.h>
#include <linux/export.h>

+#include <rdma/ib.h>
+
#include "qib.h"
#include "qib_common.h"
#include "qib_user_sdma.h"
@@ -2057,6 +2059,9 @@ static ssize_t qib_write(struct file *fp, const char __user *data,
ssize_t ret = 0;
void *dest;

+ if (WARN_ON_ONCE(!ib_safe_file_access(fp)))
+ return -EACCES;
+
if (count < sizeof(cmd.type)) {
ret = -EINVAL;
goto bail;
diff --git a/include/rdma/ib.h b/include/rdma/ib.h
index cf8f9e700e48..a6b93706b0fc 100644
--- a/include/rdma/ib.h
+++ b/include/rdma/ib.h
@@ -34,6 +34,7 @@
#define _RDMA_IB_H

#include <linux/types.h>
+#include <linux/sched.h>

struct ib_addr {
union {
@@ -86,4 +87,19 @@ struct sockaddr_ib {
__u64 sib_scope_id;
};

+/*
+ * The IB interfaces that use write() as bi-directional ioctl() are
+ * fundamentally unsafe, since there are lots of ways to trigger "write()"
+ * calls from various contexts with elevated privileges. That includes the
+ * traditional suid executable error message writes, but also various kernel
+ * interfaces that can write to file descriptors.
+ *
+ * This function provides protection for the legacy API by restricting the
+ * calling context.
+ */
+static inline bool ib_safe_file_access(struct file *filp)
+{
+ return filp->f_cred == current_cred() && segment_eq(get_fs(), USER_DS);
+}
+
#endif /* _RDMA_IB_H */
--
2.5.5