[net-next] tcp: correctly handle increased zerocopy args struct size

[Arjun Roy]

From: Arjun Roy <arjun...@google.com>

A prior patch increased the size of struct tcp_zerocopy_receive
but did not update do_tcp_getsockopt() handling to properly account
for this.

This patch simply reintroduces content erroneously cut from the
referenced prior patch that handles the new struct size.

Fixes: 18fb76ed5386 ("net-zerocopy: Copy straggler unaligned data for TCP Rx. 
zerocopy.")
Signed-off-by: Arjun Roy <arjun...@google.com>
Signed-off-by: Eric Dumazet <eduma...@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soh...@google.com>

---
 net/ipv4/tcp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 3c99d48b65d8..ed42d2193c5c 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4082,7 +4082,7 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
        }
 #ifdef CONFIG_MMU
        case TCP_ZEROCOPY_RECEIVE: {
-               struct tcp_zerocopy_receive zc;
+               struct tcp_zerocopy_receive zc = {};
                int err;
 
                if (get_user(len, optlen))
@@ -4099,7 +4099,7 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
                lock_sock(sk);
                err = tcp_zerocopy_receive(sk, &zc);
                release_sock(sk);
-               if (len == sizeof(zc))
+               if (len >= offsetofend(struct tcp_zerocopy_receive, err))
                        goto zerocopy_rcv_sk_err;
                switch (len) {
                case offsetofend(struct tcp_zerocopy_receive, err):
-- 
2.29.2.576.ga3fc446d84-goog