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packet: copy user buffers before orphan or clone

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tpacket_snd sends packets with user pages linked into skb frags. It
notifies that pages can be reused when the skb is released by setting
skb->destructor to tpacket_destruct_skb.

This can cause data corruption if the skb is orphaned (e.g., on
transmit through veth) or cloned (e.g., on mirror to another psock).

Create a kernel-private copy of data in these cases, same as tun/tap
zerocopy transmission. Reuse that infrastructure: mark the skb as
SKBTX_ZEROCOPY_FRAG, which will trigger copy in skb_orphan_frags(_rx).

Unlike other zerocopy packets, do not set shinfo destructor_arg to
struct ubuf_info. tpacket_destruct_skb already uses that ptr to notify
when the original skb is released and a timestamp is recorded. Do not
change this timestamp behavior. The ubuf_info->callback is not needed
anyway, as no zerocopy notification is expected.

Mark destructor_arg as not-a-uarg by setting the lower bit to 1. The
resulting value is not a valid ubuf_info pointer, nor a valid
tpacket_snd frame address. Add skb_zcopy_.._nouarg helpers for this.

The fix relies on features introduced in commit 52267790ef ("sock:
add MSG_ZEROCOPY"), so can be backported as is only to 4.14.

Tested with from `./in_netns.sh ./txring_overwrite` from
http://github.com/wdebruij/kerneltools/tests

Fixes: 69e3c75f4d ("net: TX_RING and packet mmap")
Reported-by: Anand H. Krishnan <[email protected]>
Signed-off-by: Willem de Bruijn <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Willem de Bruijn 2018-11-20 13:00:18 -05:00 • committed by David S. Miller
commit 5cd8d46ea1
2 changed files with 19 additions and 3 deletions
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4
net/packet/af_packet.c
View file

@ -2394,7 +2394,7 @@ static void tpacket_destruct_skb(struct sk_buff *skb)
void *ph;
__u32 ts;
ph = skb_shinfo(skb)->destructor_arg;
ph = skb_zcopy_get_nouarg(skb);
packet_dec_pending(&po->tx_ring);
ts = __packet_set_timestamp(po, ph, skb);
@ -2461,7 +2461,7 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
skb->mark = po->sk.sk_mark;
skb->tstamp = sockc->transmit_time;
sock_tx_timestamp(&po->sk, sockc->tsflags, &skb_shinfo(skb)->tx_flags);
skb_shinfo(skb)->destructor_arg = ph.raw;
skb_zcopy_set_nouarg(skb, ph.raw);
skb_reserve(skb, hlen);
skb_reset_network_header(skb);