atm: zatm: Fix potential Spectre v1

pool 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/atm/zatm.c:1462 zatm_ioctl() warn: potential spectre issue
'zatm_dev->pool_info' (local cap)

Fix this by sanitizing pool before using it to index
zatm_dev->pool_info

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: David S. Miller <davem@davemloft.net>

diff --git a/drivers/atm/zatm.c b/drivers/atm/zatm.c
index 1ef67db03c8e618d7d2425a33e5d359e89f85607..9c9a229587176d560419c0c9c4df9562c1279a75 100644 (file)
--- a/drivers/atm/zatm.c
+++ b/drivers/atm/zatm.c
@@ -28,6 +28,7 @@
 #include <asm/io.h>
 #include <linux/atomic.h>
 #include <linux/uaccess.h>
+#include <linux/nospec.h>
 
 #include "uPD98401.h"
 #include "uPD98402.h"
@@ -1458,6 +1459,8 @@ static int zatm_ioctl(struct atm_dev *dev,unsigned int cmd,void __user *arg)
                                        return -EFAULT;
                                if (pool < 0 || pool > ZATM_LAST_POOL)
                                        return -EINVAL;
+                               pool = array_index_nospec(pool,
+                                                         ZATM_LAST_POOL + 1);
                                spin_lock_irqsave(&zatm_dev->lock, flags);
                                info = zatm_dev->pool_info[pool];
                                if (cmd == ZATM_GETPOOLZ) {