net: always initialize pagedlen

mainline inclusion
from mainline-4.20
commit aba36930a35e
category: bugfix
bugzilla: 6118
CVE: NA

-------------------------------------------------

In ip packet generation, pagedlen is initialized for each skb at the
start of the loop in __ip(6)_append_data, before label alloc_new_skb.

Depending on compiler options, code can be generated that jumps to
this label, triggering use of an an uninitialized variable.

In practice, at -O2, the generated code moves the initialization below
the label. But the code should not rely on that for correctness.

Fixes: 15e36f5b ("udp: paged allocation with gso")
Signed-off-by: NWillem de Bruijn <willemb@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NKeefe LIU <liuqifa@huawei.com>
Reviewed-by: NWei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

net/ipv4/ip_output.c

@@ -939,7 +939,7 @@ static int __ip_append_data(struct sock *sk,
 			unsigned int fraglen;
 			unsigned int fraggap;
 			unsigned int alloclen;
-			unsigned int pagedlen = 0;
+			unsigned int pagedlen;
 			struct sk_buff *skb_prev;
 alloc_new_skb:
 			skb_prev = skb;
@@ -956,6 +956,7 @@ static int __ip_append_data(struct sock *sk,
 			if (datalen > mtu - fragheaderlen)
 				datalen = maxfraglen - fragheaderlen;
 			fraglen = datalen + fragheaderlen;
+			pagedlen = 0;
 
 			if ((flags & MSG_MORE) &&
 			    !(rt->dst.dev->features&NETIF_F_SG))

net/ipv6/ip6_output.c

@@ -1355,7 +1355,7 @@ static int __ip6_append_data(struct sock *sk,
 			unsigned int fraglen;
 			unsigned int fraggap;
 			unsigned int alloclen;
-			unsigned int pagedlen = 0;
+			unsigned int pagedlen;
 alloc_new_skb:
 			/* There's no room in the current skb */
 			if (skb)
@@ -1379,6 +1379,7 @@ static int __ip6_append_data(struct sock *sk,
 			if (datalen > (cork->length <= mtu && !(cork->flags & IPCORK_ALLFRAG) ? mtu : maxfraglen) - fragheaderlen)
 				datalen = maxfraglen - fragheaderlen - rt->dst.trailer_len;
 			fraglen = datalen + fragheaderlen;
+			pagedlen = 0;
 
 			if ((flags & MSG_MORE) &&
 			    !(rt->dst.dev->features&NETIF_F_SG))