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From:   Phillip Potter <phil@philpotter.co.uk>
To:     davem@davemloft.net
Cc:     kuba@kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] net: tun: set tun->dev->addr_len during TUNSETLINK processing
Date:   Mon,  5 Apr 2021 12:35:55 +0100
Message-Id: <20210405113555.9419-1-phil@philpotter.co.uk>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

When changing type with TUNSETLINK ioctl command, set tun->dev->addr_len
to match the appropriate type, using new tun_get_addr_len utility function
which returns appropriate address length for given type. Fixes a
KMSAN-found uninit-value bug reported by syzbot at:
https://syzkaller.appspot.com/bug?id=0766d38c656abeace60621896d705743aeefed51

Reported-by: syzbot+001516d86dbe88862cec@syzkaller.appspotmail.com
Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
---
 drivers/net/tun.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 978ac0981d16..56c26339ee3b 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -69,6 +69,14 @@
 #include <linux/bpf.h>
 #include <linux/bpf_trace.h>
 #include <linux/mutex.h>
+#include <linux/ieee802154.h>
+#include <linux/if_ltalk.h>
+#include <uapi/linux/if_fddi.h>
+#include <uapi/linux/if_hippi.h>
+#include <uapi/linux/if_fc.h>
+#include <net/ax25.h>
+#include <net/rose.h>
+#include <net/6lowpan.h>
 
 #include <linux/uaccess.h>
 #include <linux/proc_fs.h>
@@ -2925,6 +2933,45 @@ static int tun_set_ebpf(struct tun_struct *tun, struct tun_prog __rcu **prog_p,
 	return __tun_set_ebpf(tun, prog_p, prog);
 }
 
+/* Return correct value for tun->dev->addr_len based on tun->dev->type. */
+static inline unsigned char tun_get_addr_len(unsigned short type)
+{
+	switch (type) {
+	case ARPHRD_IP6GRE:
+	case ARPHRD_TUNNEL6:
+		return sizeof(struct in6_addr);
+	case ARPHRD_IPGRE:
+	case ARPHRD_TUNNEL:
+	case ARPHRD_SIT:
+		return 4;
+	case ARPHRD_ETHER:
+		return ETH_ALEN;
+	case ARPHRD_IEEE802154:
+	case ARPHRD_IEEE802154_MONITOR:
+		return IEEE802154_EXTENDED_ADDR_LEN;
+	case ARPHRD_PHONET_PIPE:
+	case ARPHRD_PPP:
+	case ARPHRD_NONE:
+		return 0;
+	case ARPHRD_6LOWPAN:
+		return EUI64_ADDR_LEN;
+	case ARPHRD_FDDI:
+		return FDDI_K_ALEN;
+	case ARPHRD_HIPPI:
+		return HIPPI_ALEN;
+	case ARPHRD_IEEE802:
+		return FC_ALEN;
+	case ARPHRD_ROSE:
+		return ROSE_ADDR_LEN;
+	case ARPHRD_NETROM:
+		return AX25_ADDR_LEN;
+	case ARPHRD_LOCALTLK:
+		return LTALK_ALEN;
+	default:
+		return 0;
+	}
+}
+
 static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 			    unsigned long arg, int ifreq_len)
 {
@@ -3088,6 +3135,7 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 				break;
 			}
 			tun->dev->type = (int) arg;
+			tun->dev->addr_len = tun_get_addr_len(tun->dev->type);
 			netif_info(tun, drv, tun->dev, "linktype set to %d\n",
 				   tun->dev->type);
 			call_netdevice_notifiers(NETDEV_POST_TYPE_CHANGE,
-- 
2.30.2