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Subject[PATCH 4.14 17/59] ip: on queued skb use skb_header_pointer instead of pskb_may_pull
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

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

From: Willem de Bruijn <willemb@google.com>

[ Upstream commit 4a06fa67c4da20148803525151845276cdb995c1 ]

Commit 2efd4fca703a ("ip: in cmsg IP(V6)_ORIGDSTADDR call
pskb_may_pull") avoided a read beyond the end of the skb linear
segment by calling pskb_may_pull.

That function can trigger a BUG_ON in pskb_expand_head if the skb is
shared, which it is when when peeking. It can also return ENOMEM.

Avoid both by switching to safer skb_header_pointer.

Fixes: 2efd4fca703a ("ip: in cmsg IP(V6)_ORIGDSTADDR call pskb_may_pull")
Reported-by: syzbot <syzkaller@googlegroups.com>
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/ip_sockglue.c | 12 +++++-------
net/ipv6/datagram.c | 10 ++++------
2 files changed, 9 insertions(+), 13 deletions(-)

--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -146,19 +146,17 @@ static void ip_cmsg_recv_security(struct

static void ip_cmsg_recv_dstaddr(struct msghdr *msg, struct sk_buff *skb)
{
+ __be16 _ports[2], *ports;
struct sockaddr_in sin;
- __be16 *ports;
- int end;
-
- end = skb_transport_offset(skb) + 4;
- if (end > 0 && !pskb_may_pull(skb, end))
- return;

/* All current transport protocols have the port numbers in the
* first four bytes of the transport header and this function is
* written with this assumption in mind.
*/
- ports = (__be16 *)skb_transport_header(skb);
+ ports = skb_header_pointer(skb, skb_transport_offset(skb),
+ sizeof(_ports), &_ports);
+ if (!ports)
+ return;

sin.sin_family = AF_INET;
sin.sin_addr.s_addr = ip_hdr(skb)->daddr;
--- a/net/ipv6/datagram.c
+++ b/net/ipv6/datagram.c
@@ -709,17 +709,15 @@ void ip6_datagram_recv_specific_ctl(stru
}
if (np->rxopt.bits.rxorigdstaddr) {
struct sockaddr_in6 sin6;
- __be16 *ports;
- int end;
+ __be16 _ports[2], *ports;

- end = skb_transport_offset(skb) + 4;
- if (end <= 0 || pskb_may_pull(skb, end)) {
+ ports = skb_header_pointer(skb, skb_transport_offset(skb),
+ sizeof(_ports), &_ports);
+ if (ports) {
/* All current transport protocols have the port numbers in the
* first four bytes of the transport header and this function is
* written with this assumption in mind.
*/
- ports = (__be16 *)skb_transport_header(skb);
-
sin6.sin6_family = AF_INET6;
sin6.sin6_addr = ipv6_hdr(skb)->daddr;
sin6.sin6_port = ports[1];

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