__team_change_mode() clears team->ops with memset() before restoring
safe dummy handlers via team_adjust_ops(). A concurrent team_xmit()
running under RCU on another CPU can read team->ops.transmit during
this window and call a NULL function pointer, crashing the kernel.
The race requires a mode change (CAP_NET_ADMIN) concurrent with
transmit on the team device.
BUG: kernel NULL pointer dereference, address: 0000000000000000
Oops: 0010 [#1] SMP KASAN NOPTI
RIP: 0010:0x0
Call Trace:
team_xmit (drivers/net/team/team_core.c:1853)
dev_hard_start_xmit (net/core/dev.c:3904)
__dev_queue_xmit (net/core/dev.c:4871)
packet_sendmsg (net/packet/af_packet.c:3109)
__sys_sendto (net/socket.c:2265)
The original code assumed that no ports means no traffic, so mode
changes could freely memset()/memcpy() the ops. AF_PACKET with
forced carrier breaks that assumption.
Prevent the race instead of making it safe: replace memset()/memcpy()
with per-field updates that never touch transmit or receive. Those
two handlers are managed solely by team_adjust_ops(), which already
installs dummies when tx_en_port_count == 0 (always true during mode
change since no ports are present). WRITE_ONCE/READ_ONCE prevent
store/load tearing on the handler pointers.
synchronize_net() before exit_op() drains in-flight readers that may
still reference old mode state from before port removal switched the
handlers to dummies.
Fixes: 3d249d4ca7 ("net: introduce ethernet teaming device")
Reported-by: Xiang Mei <xmei5@asu.edu>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Link: https://patch.msgid.link/20260521081159.1491563-3-bestswngs@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
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