IB/ucm: Fix Spectre v1 vulnerability

hdr.cmd can be indirectly controlled by user-space, hence leading to
a potential exploitation of the Spectre variant 1 vulnerability.

This issue was detected with the help of Smatch:

drivers/infiniband/core/ucm.c:1127 ib_ucm_write() warn: potential
spectre issue 'ucm_cmd_table' [r] (local cap)

Fix this by sanitizing hdr.cmd before using it to index
ucm_cmd_table.

Notice that given that speculation windows are large, the policy is
to kill the speculation on the first load and not worry if it can be
completed with a dependent load/store [1].

[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

Cc: stable@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
CVE-2017-5753

(cherry picked from commit 0295e39595e1146522f2722715dba7f7fba42217)
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/infiniband/core/ucm.c b/drivers/infiniband/core/ucm.c
index f2a7f62c2834fac07b9712db723c144c8986b9dd..09cb24353be39f116d88afe63ad56a718c43b21d 100644 (file)
--- a/drivers/infiniband/core/ucm.c
+++ b/drivers/infiniband/core/ucm.c
@@ -46,6 +46,8 @@
 #include <linux/mutex.h>
 #include <linux/slab.h>
 
+#include <linux/nospec.h>
+
 #include <linux/uaccess.h>
 
 #include <rdma/ib.h>
@@ -1118,6 +1120,7 @@ static ssize_t ib_ucm_write(struct file *filp, const char __user *buf,
 
        if (hdr.cmd >= ARRAY_SIZE(ucm_cmd_table))
                return -EINVAL;
+       hdr.cmd = array_index_nospec(hdr.cmd, ARRAY_SIZE(ucm_cmd_table));
 
        if (hdr.in + sizeof(hdr) > len)
                return -EINVAL;