tcp: add sanity tests to TCP_QUEUE_SEQ

Qingyu Li reported a syzkaller bug where the repro
changes RCV SEQ _after_ restoring data in the receive queue.

mprotect(0x4aa000, 12288, PROT_READ) = 0
mmap(0x1ffff000, 4096, PROT_NONE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x1ffff000
mmap(0x20000000, 16777216, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x20000000
mmap(0x21000000, 4096, PROT_NONE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x21000000
socket(AF_INET6, SOCK_STREAM, IPPROTO_IP) = 3
setsockopt(3, SOL_TCP, TCP_REPAIR, [1], 4) = 0
connect(3, {sa_family=AF_INET6, sin6_port=htons(0), sin6_flowinfo=htonl(0), inet_pton(AF_INET6, "::1", &sin6_addr), sin6_scope_id=0}, 28) = 0
setsockopt(3, SOL_TCP, TCP_REPAIR_QUEUE, [1], 4) = 0
sendmsg(3, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="0x0000000000000003\0\0", iov_len=20}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 20
setsockopt(3, SOL_TCP, TCP_REPAIR, [0], 4) = 0
setsockopt(3, SOL_TCP, TCP_QUEUE_SEQ, [128], 4) = 0
recvfrom(3, NULL, 20, 0, NULL, NULL) = -1 ECONNRESET (Connection reset by peer)

syslog shows:
[ 111.205099] TCP recvmsg seq # bug 2: copied 80, seq 0, rcvnxt 80, fl 0
[ 111.207894] WARNING: CPU: 1 PID: 356 at net/ipv4/tcp.c:2343 tcp_recvmsg_locked+0x90e/0x29a0

This should not be allowed. TCP_QUEUE_SEQ should only be used
when queues are empty.

This patch fixes this case, and the tx path as well.

Fixes: ee9952831cfd ("tcp: Initial repair mode")
Signed-off-by: Eric Dumazet <[e-mail]>
Cc: Pavel Emelyanov <[e-mail]>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=212005
Reported-by: Qingyu Li <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv4/tcp.c

···
 		break;
 
 	case TCP_QUEUE_SEQ:
-		if (sk->sk_state != TCP_CLOSE)
+		if (sk->sk_state != TCP_CLOSE) {
 			err = -EPERM;
-		else if (tp->repair_queue == TCP_SEND_QUEUE)
-			WRITE_ONCE(tp->write_seq, val);
-		else if (tp->repair_queue == TCP_RECV_QUEUE) {
-			WRITE_ONCE(tp->rcv_nxt, val);
-			WRITE_ONCE(tp->copied_seq, val);
-		}
-		else
+		} else if (tp->repair_queue == TCP_SEND_QUEUE) {
+			if (!tcp_rtx_queue_empty(sk))
+				err = -EPERM;
+			else
+				WRITE_ONCE(tp->write_seq, val);
+		} else if (tp->repair_queue == TCP_RECV_QUEUE) {
+			if (tp->rcv_nxt != tp->copied_seq) {
+				err = -EPERM;
+			} else {
+				WRITE_ONCE(tp->rcv_nxt, val);
+				WRITE_ONCE(tp->copied_seq, val);
+			}
+		} else {
 			err = -EINVAL;
+		}
 		break;
 
 	case TCP_REPAIR_OPTIONS: