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packet: copy user buffers before orphan or clone 

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 <anandhkrishnan@gmail.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 2018-11-20 13:00:18 -05:00 committed by David S. Miller
parent 039e70a70c
commit 5cd8d46ea1
2 changed files with 19 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
include/linux/skbuff.h
View File

@ -1326,6 +1326,22 @@ static inline void skb_zcopy_set(struct sk_buff *skb, struct ubuf_info *uarg)
} }
} }
static inline void skb_zcopy_set_nouarg(struct sk_buff *skb, void *val)
{
skb_shinfo(skb)->destructor_arg = (void *)((uintptr_t) val | 0x1UL);
skb_shinfo(skb)->tx_flags |= SKBTX_ZEROCOPY_FRAG;
}
static inline bool skb_zcopy_is_nouarg(struct sk_buff *skb)
{
return (uintptr_t) skb_shinfo(skb)->destructor_arg & 0x1UL;
}
static inline void *skb_zcopy_get_nouarg(struct sk_buff *skb)
{
return (void *)((uintptr_t) skb_shinfo(skb)->destructor_arg & ~0x1UL);
}
/* Release a reference on a zerocopy structure */ /* Release a reference on a zerocopy structure */
static inline void skb_zcopy_clear(struct sk_buff *skb, bool zerocopy) static inline void skb_zcopy_clear(struct sk_buff *skb, bool zerocopy)
{ {
@ -1335,7 +1351,7 @@ static inline void skb_zcopy_clear(struct sk_buff *skb, bool zerocopy)
if (uarg->callback == sock_zerocopy_callback) { if (uarg->callback == sock_zerocopy_callback) {
uarg->zerocopy = uarg->zerocopy && zerocopy; uarg->zerocopy = uarg->zerocopy && zerocopy;
sock_zerocopy_put(uarg); sock_zerocopy_put(uarg);
} else { } else if (!skb_zcopy_is_nouarg(skb)) {
uarg->callback(uarg, zerocopy); uarg->callback(uarg, zerocopy);
} }

4
net/packet/af_packet.c
View File

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