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:1491 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

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 a8d2eb0ceb8d8f78788182f81f8e1e9f9dc8fbbb..2c288d1f42bba0fcdf31ccec72c069bfa60688b9 100644 (file)
--- a/drivers/atm/zatm.c
+++ b/drivers/atm/zatm.c
@@ -1483,6 +1483,8 @@ 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);
                                if (copy_from_user(&info,
                                    &((struct zatm_pool_req __user *) arg)->info,
                                    sizeof(info))) return -EFAULT;