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net-timestamp: avoid use-after-free in ip_recv_error

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Syzkaller reported a use-after-free in ip_recv_error at line

    info->ipi_ifindex = skb->dev->ifindex;

This function is called on dequeue from the error queue, at which
point the device pointer may no longer be valid.

Save ifindex on enqueue in __skb_complete_tx_timestamp, when the
pointer is valid or NULL. Store it in temporary storage skb->cb.

It is safe to reference skb->dev here, as called from device drivers
or dev_queue_xmit. The exception is when called from tcp_ack_tstamp;
in that case it is NULL and ifindex is set to 0 (invalid).

Do not return a pktinfo cmsg if ifindex is 0. This maintains the
current behavior of not returning a cmsg if skb->dev was NULL.

On dequeue, the ipv4 path will cast from sock_exterr_skb to
in_pktinfo. Both have ifindex as their first element, so no explicit
conversion is needed. This is by design, introduced in commit
0b922b7a82 ("net: original ingress device index in PKTINFO"). For
ipv6 ip6_datagram_support_cmsg converts to in6_pktinfo.

Fixes: 829ae9d611 ("net-timestamp: allow reading recv cmsg on errqueue with origin tstamp")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Willem de Bruijn 2017-04-12 19:24:35 -04:00 committed by David S. Miller
parent 1215e51eda
commit 1862d6208d
3 changed files with 6 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
net/core/skbuff.c
View File

@ -3807,6 +3807,7 @@ static void __skb_complete_tx_timestamp(struct sk_buff *skb,
serr->ee.ee_origin = SO_EE_ORIGIN_TIMESTAMPING;
serr->ee.ee_info = tstype;
serr->opt_stats = opt_stats;
serr->header.h4.iif = skb->dev ? skb->dev->ifindex : 0;
if (sk->sk_tsflags & SOF_TIMESTAMPING_OPT_ID) {
serr->ee.ee_data = skb_shinfo(skb)->tskey;
if (sk->sk_protocol == IPPROTO_TCP &&

9
net/ipv4/ip_sockglue.c
View File

@ -488,16 +488,15 @@ static bool ipv4_datagram_support_cmsg(const struct sock *sk,
return false;
/* Support IP_PKTINFO on tstamp packets if requested, to correlate
* timestamp with egress dev. Not possible for packets without dev
* timestamp with egress dev. Not possible for packets without iif
* or without payload (SOF_TIMESTAMPING_OPT_TSONLY).
*/
if ((!(sk->sk_tsflags & SOF_TIMESTAMPING_OPT_CMSG)) ||
(!skb->dev))
info = PKTINFO_SKB_CB(skb);
if (!(sk->sk_tsflags & SOF_TIMESTAMPING_OPT_CMSG) ||
!info->ipi_ifindex)
return false;
info = PKTINFO_SKB_CB(skb);
info->ipi_spec_dst.s_addr = ip_hdr(skb)->saddr;
info->ipi_ifindex = skb->dev->ifindex;
return true;
}

10
net/ipv6/datagram.c
View File

@ -405,9 +405,6 @@ static inline bool ipv6_datagram_support_addr(struct sock_exterr_skb *serr)
* At one point, excluding local errors was a quick test to identify icmp/icmp6
* errors. This is no longer true, but the test remained, so the v6 stack,
* unlike v4, also honors cmsg requests on all wifi and timestamp errors.
*
* Timestamp code paths do not initialize the fields expected by cmsg:
* the PKTINFO fields in skb->cb[]. Fill those in here.
*/
static bool ip6_datagram_support_cmsg(struct sk_buff *skb,
struct sock_exterr_skb *serr)
@ -419,14 +416,9 @@ static bool ip6_datagram_support_cmsg(struct sk_buff *skb,
if (serr->ee.ee_origin == SO_EE_ORIGIN_LOCAL)
return false;
if (!skb->dev)
if (!IP6CB(skb)->iif)
return false;
if (skb->protocol == htons(ETH_P_IPV6))
IP6CB(skb)->iif = skb->dev->ifindex;
else
PKTINFO_SKB_CB(skb)->ipi_ifindex = skb->dev->ifindex;
return true;
}