From efe967cdec32af93e15839cc639695ec5f637771 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Fri, 28 Jul 2017 16:41:37 +0200 Subject: [PATCH] tcp: avoid bogus gcc-7 array-bounds warning When using CONFIG_UBSAN_SANITIZE_ALL, the TCP code produces a false-positive warning: net/ipv4/tcp_output.c: In function 'tcp_connect': net/ipv4/tcp_output.c:2207:40: error: array subscript is below array bounds [-Werror=array-bounds] tp->chrono_stat[tp->chrono_type - 1] += now - tp->chrono_start; ^~ net/ipv4/tcp_output.c:2207:40: error: array subscript is below array bounds [-Werror=array-bounds] tp->chrono_stat[tp->chrono_type - 1] += now - tp->chrono_start; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~ I have opened a gcc bug for this, but distros have already shipped compilers with this problem, and it's not clear yet whether there is a way for gcc to avoid the warning. As the problem is related to the bitfield access, this introduces a temporary variable to store the old enum value. I did not notice this warning earlier, since UBSAN is disabled when building with COMPILE_TEST, and that was always turned on in both allmodconfig and randconfig tests. Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81601 Signed-off-by: Arnd Bergmann Signed-off-by: David S. Miller --- net/ipv4/tcp_output.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 4e985dea1dd2..2f1588bf73da 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -2202,9 +2202,10 @@ static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb, static void tcp_chrono_set(struct tcp_sock *tp, const enum tcp_chrono new) { const u32 now = tcp_jiffies32; + enum tcp_chrono old = tp->chrono_type; - if (tp->chrono_type > TCP_CHRONO_UNSPEC) - tp->chrono_stat[tp->chrono_type - 1] += now - tp->chrono_start; + if (old > TCP_CHRONO_UNSPEC) + tp->chrono_stat[old - 1] += now - tp->chrono_start; tp->chrono_start = now; tp->chrono_type = new; }