linux-kernel - [PATCH for 4.9 02/39] net/packet: check length in getsockopt() called with PACKET

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Date:   Mon, 18 Sep 2017 00:19:37 +0000
From:   "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Cc:     Alexander Potapenko <glider@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>
Subject: [PATCH for 4.9 02/39] net/packet: check length in getsockopt() called
 with PACKET_HDRLEN

From: Alexander Potapenko <glider@...gle.com>

[ Upstream commit fd2c83b35752f0a8236b976978ad4658df14a59f ]

In the case getsockopt() is called with PACKET_HDRLEN and optlen < 4
|val| remains uninitialized and the syscall may behave differently
depending on its value, and even copy garbage to userspace on certain
architectures. To fix this we now return -EINVAL if optlen is too small.

This bug has been detected with KMSAN.

Signed-off-by: Alexander Potapenko <glider@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
---
 net/packet/af_packet.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index ae7bfd26cd91..2cf706f7defa 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3878,6 +3878,8 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
 	case PACKET_HDRLEN:
 		if (len > sizeof(int))
 			len = sizeof(int);
+		if (len < sizeof(int))
+			return -EINVAL;
 		if (copy_from_user(&val, optval, len))
 			return -EFAULT;
 		switch (val) {
-- 
2.11.0