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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Willem de Bruijn <willemb@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.19 072/639] net: always initialize pagedlen
Date:   Fri, 24 Jan 2020 10:24:02 +0100
Message-Id: <20200124093056.417796600@linuxfoundation.org>
In-Reply-To: <20200124093047.008739095@linuxfoundation.org>
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From: Willem de Bruijn <willemb@google.com>

[ Upstream commit aba36930a35e7f1fe1319b203f25c05d6c119936 ]

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: 15e36f5b8e98 ("udp: paged allocation with gso")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/ipv4/ip_output.c  | 3 ++-
 net/ipv6/ip6_output.c | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index d63091812342f..fbf30122e8bf2 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -940,7 +940,7 @@ 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;
@@ -957,6 +957,7 @@ alloc_new_skb:
 			if (datalen > mtu - fragheaderlen)
 				datalen = maxfraglen - fragheaderlen;
 			fraglen = datalen + fragheaderlen;
+			pagedlen = 0;
 
 			if ((flags & MSG_MORE) &&
 			    !(rt->dst.dev->features&NETIF_F_SG))
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index eed9231c90ad5..9886a84c25117 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1357,7 +1357,7 @@ emsgsize:
 			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)
@@ -1381,6 +1381,7 @@ alloc_new_skb:
 			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))
-- 
2.20.1