netdev - [PATCH v2] slcan: Don't transmit uninitialized stack data in padding

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Message-Id: <20200401100639.20199-1-rpalethorpe@suse.com>
Date:   Wed,  1 Apr 2020 12:06:39 +0200
From:   Richard Palethorpe <rpalethorpe@...e.com>
To:     linux-can@...r.kernel.org
Cc:     Richard Palethorpe <rpalethorpe@...e.com>,
        Kees Cook <keescook@...omium.org>, netdev@...r.kernel.org,
        security@...nel.org, wg@...ndegger.com, mkl@...gutronix.de,
        davem@...emloft.net
Subject: [PATCH v2] slcan: Don't transmit uninitialized stack data in padding

struct can_frame contains some padding which is not explicitly zeroed in
slc_bump. This uninitialized data will then be transmitted if the stack
initialization hardening feature is not enabled (CONFIG_INIT_STACK_ALL).

This commit just zeroes the whole struct including the padding.

Signed-off-by: Richard Palethorpe <rpalethorpe@...e.com>
Fixes: a1044e36e457 ("can: add slcan driver for serial/USB-serial CAN adapters")
Reviewed-by: Kees Cook <keescook@...omium.org>
Cc: linux-can@...r.kernel.org
Cc: netdev@...r.kernel.org
Cc: security@...nel.org
Cc: wg@...ndegger.com
Cc: mkl@...gutronix.de
Cc: davem@...emloft.net
---

V2: Reviewed by Kees and Fixes tag added.

As mentioned in V1; The following unfinished test can reproduce the bug:
https://github.com/richiejp/ltp/blob/pty-slcan/testcases/kernel/pty/pty04.c


 drivers/net/can/slcan.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/net/can/slcan.c b/drivers/net/can/slcan.c
index a3664281a33f..4dfa459ef5c7 100644
--- a/drivers/net/can/slcan.c
+++ b/drivers/net/can/slcan.c
@@ -148,7 +148,7 @@ static void slc_bump(struct slcan *sl)
 	u32 tmpid;
 	char *cmd = sl->rbuff;
 
-	cf.can_id = 0;
+	memset(&cf, 0, sizeof(cf));
 
 	switch (*cmd) {
 	case 'r':
@@ -187,8 +187,6 @@ static void slc_bump(struct slcan *sl)
 	else
 		return;
 
-	*(u64 *) (&cf.data) = 0; /* clear payload */
-
 	/* RTR frames may have a dlc > 0 but they never have any data bytes */
 	if (!(cf.can_id & CAN_RTR_FLAG)) {
 		for (i = 0; i < cf.can_dlc; i++) {
-- 
2.24.0