Ricardo Dias 01770a1661 tcp: fix race condition when creating child sockets from syncookies ... When the TCP stack is in SYN flood mode, the server child socket is created from the SYN cookie received in a TCP packet with the ACK flag set. The child socket is created when the server receives the first TCP packet with a valid SYN cookie from the client. Usually, this packet corresponds to the final step of the TCP 3-way handshake, the ACK packet. But is also possible to receive a valid SYN cookie from the first TCP data packet sent by the client, and thus create a child socket from that SYN cookie. Since a client socket is ready to send data as soon as it receives the SYN+ACK packet from the server, the client can send the ACK packet (sent by the TCP stack code), and the first data packet (sent by the userspace program) almost at the same time, and thus the server will equally receive the two TCP packets with valid SYN cookies almost at the same instant. When such event happens, the TCP stack code has a race condition that occurs between the momement a lookup is done to the established connections hashtable to check for the existence of a connection for the same client, and the moment that the child socket is added to the established connections hashtable. As a consequence, this race condition can lead to a situation where we add two child sockets to the established connections hashtable and deliver two sockets to the userspace program to the same client. This patch fixes the race condition by checking if an existing child socket exists for the same client when we are adding the second child socket to the established connections socket. If an existing child socket exists, we drop the packet and discard the second child socket to the same client. Signed-off-by: Ricardo Dias <rdias@singlestore.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Link: https://lore.kernel.org/r/20201120111133.GA67501@rdias-suse-pc.lan Signed-off-by: Jakub Kicinski <kuba@kernel.org>		2020-11-23 16:32:33 -08:00
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ccids	net: dccp: Convert to use the preferred fallthrough macro	2020-08-22 12:38:34 -07:00
ackvec.c	net: dccp: delete repeated words	2020-08-24 17:31:20 -07:00
ackvec.h
ccid.c
ccid.h	net: dccp: Replace zero-length array with flexible-array member	2020-02-28 12:08:37 -08:00
dccp.h	net: pass a sockptr_t into ->setsockopt	2020-07-24 15:41:54 -07:00
diag.c	inet_diag: Move the INET_DIAG_REQ_BYTECODE nlattr to cb->data	2020-02-27 18:50:19 -08:00
feat.c	net: dccp: Convert to use the preferred fallthrough macro	2020-08-22 12:38:34 -07:00
feat.h
input.c	net: dccp: Convert to use the preferred fallthrough macro	2020-08-22 12:38:34 -07:00
ipv4.c	tcp: fix race condition when creating child sockets from syncookies	2020-11-23 16:32:33 -08:00
ipv6.c	tcp: fix race condition when creating child sockets from syncookies	2020-11-23 16:32:33 -08:00
ipv6.h
Kconfig	dccp: Replace HTTP links with HTTPS ones	2020-07-13 11:54:07 -07:00
Makefile
minisocks.c
options.c	net: dccp: Convert to use the preferred fallthrough macro	2020-08-22 12:38:34 -07:00
output.c	net: dccp: Convert to use the preferred fallthrough macro	2020-08-22 12:38:34 -07:00
proto.c	net: dccp: Convert to use the preferred fallthrough macro	2020-08-22 12:38:34 -07:00
qpolicy.c
sysctl.c
timer.c	inet: remove icsk_ack.blocked	2020-09-30 14:21:30 -07:00
trace.h