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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 commit52267790ef
("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>
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@ -1326,6 +1326,22 @@ static inline void skb_zcopy_set(struct sk_buff *skb, struct ubuf_info *uarg)
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}
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}
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static inline void skb_zcopy_set_nouarg(struct sk_buff *skb, void *val)
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{
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skb_shinfo(skb)->destructor_arg = (void *)((uintptr_t) val | 0x1UL);
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skb_shinfo(skb)->tx_flags |= SKBTX_ZEROCOPY_FRAG;
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}
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static inline bool skb_zcopy_is_nouarg(struct sk_buff *skb)
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{
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return (uintptr_t) skb_shinfo(skb)->destructor_arg & 0x1UL;
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}
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static inline void *skb_zcopy_get_nouarg(struct sk_buff *skb)
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{
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return (void *)((uintptr_t) skb_shinfo(skb)->destructor_arg & ~0x1UL);
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}
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/* Release a reference on a zerocopy structure */
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static inline void skb_zcopy_clear(struct sk_buff *skb, bool zerocopy)
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{
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@ -1335,7 +1351,7 @@ static inline void skb_zcopy_clear(struct sk_buff *skb, bool zerocopy)
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if (uarg->callback == sock_zerocopy_callback) {
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uarg->zerocopy = uarg->zerocopy && zerocopy;
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sock_zerocopy_put(uarg);
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} else {
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} else if (!skb_zcopy_is_nouarg(skb)) {
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uarg->callback(uarg, zerocopy);
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}
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@ -2394,7 +2394,7 @@ static void tpacket_destruct_skb(struct sk_buff *skb)
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void *ph;
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__u32 ts;
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ph = skb_shinfo(skb)->destructor_arg;
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ph = skb_zcopy_get_nouarg(skb);
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packet_dec_pending(&po->tx_ring);
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ts = __packet_set_timestamp(po, ph, skb);
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@ -2461,7 +2461,7 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
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skb->mark = po->sk.sk_mark;
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skb->tstamp = sockc->transmit_time;
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sock_tx_timestamp(&po->sk, sockc->tsflags, &skb_shinfo(skb)->tx_flags);
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skb_shinfo(skb)->destructor_arg = ph.raw;
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skb_zcopy_set_nouarg(skb, ph.raw);
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skb_reserve(skb, hlen);
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skb_reset_network_header(skb);
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