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nfc: af_nfc: Fix Spectre v1 vulnerability

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proto is 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:

net/nfc/af_nfc.c:42 nfc_sock_create() warn: potential spectre issue 'proto_tab' [w] (local cap)

Fix this by sanitizing proto before using it to index proto_tab.

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>
This commit is contained in:
Gustavo A. R. Silva 2018-12-21 15:47:53 -06:00 committed by David S. Miller
parent d686026b1e
commit a95386f039
1 changed files with 2 additions and 0 deletions
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2
net/nfc/af_nfc.c
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@ -21,6 +21,7 @@
#include <linux/nfc.h> #include <linux/nfc.h>
#include <linux/module.h> #include <linux/module.h>
#include <linux/nospec.h>
#include "nfc.h" #include "nfc.h"
@ -37,6 +38,7 @@ static int nfc_sock_create(struct net *net, struct socket *sock, int proto,
if (proto < 0 || proto >= NFC_SOCKPROTO_MAX) if (proto < 0 || proto >= NFC_SOCKPROTO_MAX)
return -EINVAL; return -EINVAL;
proto = array_index_nospec(proto, NFC_SOCKPROTO_MAX);
read_lock(&proto_tab_lock); read_lock(&proto_tab_lock);
if (proto_tab[proto] && try_module_get(proto_tab[proto]->owner)) { if (proto_tab[proto] && try_module_get(proto_tab[proto]->owner)) {