[PATCH net-next] tcp: return sizeof tcp_dctcp_info in dctcp_get_info()

[Neal Cardwell]

Make sure that dctcp_get_info() returns only the size of the
info->dctcp struct that it zeroes out and fills in. Previously it had
been returning the size of the enclosing tcp_cc_info union,
sizeof(*info).  There is no problem yet, but that union that may one
day be larger than struct tcp_dctcp_info, in which case the
TCP_CC_INFO code might accidentally copy uninitialized bytes from the
stack.

Signed-off-by: Neal Cardwell <ncardw...@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soh...@google.com>
Signed-off-by: Eric Dumazet <eduma...@google.com>
---
 net/ipv4/tcp_dctcp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_dctcp.c b/net/ipv4/tcp_dctcp.c
index 7e538f7..10d728b 100644
--- a/net/ipv4/tcp_dctcp.c
+++ b/net/ipv4/tcp_dctcp.c
@@ -293,7 +293,7 @@ static size_t dctcp_get_info(struct sock *sk, u32 ext, int 
*attr,
         */
        if (ext & (1 << (INET_DIAG_DCTCPINFO - 1)) ||
            ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
-               memset(info, 0, sizeof(struct tcp_dctcp_info));
+               memset(&info->dctcp, 0, sizeof(info->dctcp));
                if (inet_csk(sk)->icsk_ca_ops != &dctcp_reno) {
                        info->dctcp.dctcp_enabled = 1;
                        info->dctcp.dctcp_ce_state = (u16) ca->ce_state;
@@ -303,7 +303,7 @@ static size_t dctcp_get_info(struct sock *sk, u32 ext, int 
*attr,
                }
 
                *attr = INET_DIAG_DCTCPINFO;
-               return sizeof(*info);
+               return sizeof(info->dctcp);
        }
        return 0;
 }
-- 
2.8.0.rc3.226.g39d4020