[PATCH] atm: zatm: Fix potential Spectre v1

From: Gustavo A. R. Silva
Date: Fri Jun 29 2018 - 14:52:22 EST


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

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
---
drivers/atm/zatm.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/atm/zatm.c b/drivers/atm/zatm.c
index a8d2eb0..2c288d1 100644
--- 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;
--
2.7.4