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net: erspan: set lltx to avoid sch_direct_xmit deadlock

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The ERSPAN xmit path re-enters the network stack, causing nested
acquisition of _xmit_lock on the underlay device while already holding
the ERSPAN device's _xmit_lock, creating an ABBA deadlock. This happens
for both IPv4 ERSPAN (erspan_xmit() -> ip_tunnel_xmit()) and IPv6 ERSPAN
(ip6erspan_tunnel_xmit() -> ip6_tnl_xmit()):

  sch_direct_xmit [lock erspan] -> erspan_xmit -> ip_tunnel_xmit ->
  ip_output -> __dev_queue_xmit -> sch_direct_xmit [lock underlay]

  sch_direct_xmit [lock erspan] -> ip6erspan_tunnel_xmit -> ip6_tnl_xmit ->
  ip6_output -> __dev_queue_xmit -> sch_direct_xmit [lock underlay]

Set dev->lltx = true so HARD_TX_LOCK() skips the spinlock for ERSPAN.
This is safe as the ERSPAN xmit path has no shared mutable state: o_seqno
is atomic, TX stats are per-CPU u64_stats, dst_cache is per-CPU, and
o_flags is no longer modified in the xmit path since commit 9958e69b98
("gre: fix ERSPAN o_flags race/corruption in xmit and fill_info").
GRETAP, the sibling device with identical xmit structure, already sets
lltx.

Reported-by: syzbot+9bda1b9fbb7fbdf9b62b@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9bda1b9fbb7fbdf9b62b
Fixes: 84e54fe0a5 ("gre: introduce native tunnel support for ERSPAN")
Fixes: 5a963eb61b ("ip6_gre: Add ERSPAN native tunnel support")
Cc: stable@vger.kernel.org # 9958e69b98 ("gre: fix ERSPAN o_flags race/corruption in xmit and fill_info")
Cc: stable@vger.kernel.org
Signed-off-by: Yun Zhou <yun.zhou@windriver.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20261008093824.119453-1-yun.zhou@windriver.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Yun Zhou 2026-10-08 17:38:24 +08:00 committed by Jakub Kicinski
parent ee3deb0151
commit 2d36ec7383
2 changed files with 2 additions and 0 deletions
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1
net/ipv4/ip_gre.c
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@ -1367,6 +1367,7 @@ static int erspan_tunnel_init(struct net_device *dev)
dev->features |= GRE_FEATURES;
dev->hw_features |= GRE_FEATURES;
dev->priv_flags |= IFF_LIVE_ADDR_CHANGE;
dev->lltx = true;
netif_keep_dst(dev);
return ip_tunnel_init(dev);

1
net/ipv6/ip6_gre.c
View File

@ -1864,6 +1864,7 @@ static int ip6erspan_tap_init(struct net_device *dev)
dev->mtu -= 8;
dev->priv_flags |= IFF_LIVE_ADDR_CHANGE;
dev->lltx = true;
ip6erspan_tnl_link_config(tunnel, 1);
netdev_hold(dev, &tunnel->dev_tracker, GFP_KERNEL);