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authorPeilin Ye <peilin.ye@bytedance.com>2022-04-21 15:09:02 -0700
committerDavid S. Miller <davem@davemloft.net>2022-04-25 11:40:45 +0100
commit31c417c948d7f6909cb63f0ac3298f3c38f8ce20 (patch)
tree99159f3858c374bd6a062d37a0bc2312269eaf1b /net/ipv6
parentfde98ae91f79cab4e020f40c35ed23cbdc59661c (diff)
downloadlinux-31c417c948d7f6909cb63f0ac3298f3c38f8ce20.tar.bz2
ip_gre, ip6_gre: Fix race condition on o_seqno in collect_md mode
As pointed out by Jakub Kicinski, currently using TUNNEL_SEQ in collect_md mode is racy for [IP6]GRE[TAP] devices. Consider the following sequence of events: 1. An [IP6]GRE[TAP] device is created in collect_md mode using "ip link add ... external". "ip" ignores "[o]seq" if "external" is specified, so TUNNEL_SEQ is off, and the device is marked as NETIF_F_LLTX (i.e. it uses lockless TX); 2. Someone sets TUNNEL_SEQ on outgoing skb's, using e.g. bpf_skb_set_tunnel_key() in an eBPF program attached to this device; 3. gre_fb_xmit() or __gre6_xmit() processes these skb's: gre_build_header(skb, tun_hlen, flags, protocol, tunnel_id_to_key32(tun_info->key.tun_id), (flags & TUNNEL_SEQ) ? htonl(tunnel->o_seqno++) : 0); ^^^^^^^^^^^^^^^^^ Since we are not using the TX lock (&txq->_xmit_lock), multiple CPUs may try to do this tunnel->o_seqno++ in parallel, which is racy. Fix it by making o_seqno atomic_t. As mentioned by Eric Dumazet in commit b790e01aee74 ("ip_gre: lockless xmit"), making o_seqno atomic_t increases "chance for packets being out of order at receiver" when NETIF_F_LLTX is on. Maybe a better fix would be: 1. Do not ignore "oseq" in external mode. Users MUST specify "oseq" if they want the kernel to allow sequencing of outgoing packets; 2. Reject all outgoing TUNNEL_SEQ packets if the device was not created with "oseq". Unfortunately, that would break userspace. We could now make [IP6]GRE[TAP] devices always NETIF_F_LLTX, but let us do it in separate patches to keep this fix minimal. Suggested-by: Jakub Kicinski <kuba@kernel.org> Fixes: 77a5196a804e ("gre: add sequence number for collect md mode.") Signed-off-by: Peilin Ye <peilin.ye@bytedance.com> Acked-by: William Tu <u9012063@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv6')
-rw-r--r--net/ipv6/ip6_gre.c7
1 files changed, 4 insertions, 3 deletions
diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index d9e4ac94eab4..5136959b3dc5 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -766,7 +766,7 @@ static netdev_tx_t __gre6_xmit(struct sk_buff *skb,
gre_build_header(skb, tun_hlen,
flags, protocol,
tunnel_id_to_key32(tun_info->key.tun_id),
- (flags & TUNNEL_SEQ) ? htonl(tunnel->o_seqno++)
+ (flags & TUNNEL_SEQ) ? htonl(atomic_fetch_inc(&tunnel->o_seqno))
: 0);
} else {
@@ -777,7 +777,8 @@ static netdev_tx_t __gre6_xmit(struct sk_buff *skb,
gre_build_header(skb, tunnel->tun_hlen, flags,
protocol, tunnel->parms.o_key,
- (flags & TUNNEL_SEQ) ? htonl(tunnel->o_seqno++) : 0);
+ (flags & TUNNEL_SEQ) ? htonl(atomic_fetch_inc(&tunnel->o_seqno))
+ : 0);
}
return ip6_tnl_xmit(skb, dev, dsfield, fl6, encap_limit, pmtu,
@@ -1055,7 +1056,7 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff *skb,
/* Push GRE header. */
proto = (t->parms.erspan_ver == 1) ? htons(ETH_P_ERSPAN)
: htons(ETH_P_ERSPAN2);
- gre_build_header(skb, 8, TUNNEL_SEQ, proto, 0, htonl(t->o_seqno++));
+ gre_build_header(skb, 8, TUNNEL_SEQ, proto, 0, htonl(atomic_fetch_inc(&t->o_seqno)));
/* TooBig packet may have updated dst->dev's mtu */
if (!t->parms.collect_md && dst && dst_mtu(dst) > dst->dev->mtu)