[PATCH] tcp: Add error checking for flow_epoll_set() in tcp_flow_migrate_target()

[Stefano Brivio <sbrivio@redhat.com>]

Commit 90287c2a774e ("tcp: Register fds with epoll at flow creation")
added a call to flow_epoll_set() in tcp_flow_migrate_target() without
checking for the error code.

As Laurent explains, that's harmless, as tcp_flow_migrate_target_ext()
will clean up the flow anyway, and we'll just uselessly call
flow_hash_insert() before removing it again.

But Coverity Scan complains about the unchecked return code, so check
it, skip flow_hash_insert() in that case, and explain in comments why
we don't have to do anything else.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 tcp.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/tcp.c b/tcp.c
index 6a26826..0a6b7ff 100644
--- a/tcp.c
+++ b/tcp.c
@@ -3684,17 +3684,19 @@ int tcp_flow_migrate_target(struct ctx *c, int fd)
 
 	if ((rc = tcp_flow_repair_socket(c, conn))) {
 		flow_err(flow, "Can't set up socket: %s, drop", strerror_(-rc));
-		/* Can't leave the flow in an incomplete state */
-		FLOW_ACTIVATE(conn);
-		return 0;
+		goto out;
 	}
 
 	flow_epollid_set(&conn->f, EPOLLFD_ID_DEFAULT);
-	flow_epoll_set(&conn->f, EPOLL_CTL_ADD, 0, conn->sock, !TAPSIDE(conn));
+	if (flow_epoll_set(&conn->f, EPOLL_CTL_ADD, 0, conn->sock,
+			   !TAPSIDE(conn)))
+		goto out; /* tcp_flow_migrate_target_ext() will clean this up */
 
 	flow_hash_insert(c, TAP_SIDX(conn));
-	FLOW_ACTIVATE(conn);
 
+out:
+	/* Never leave the flow in an incomplete state */
+	FLOW_ACTIVATE(conn);
 	return 0;
 }
 
-- 
2.43.0