| Message ID | 20170728144153.2024234-1-arnd@arndb.de |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Arnd Bergmann > Sent: 28 July 2017 15:42 ... > --- 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; What a horrid combination of enum and integers. Also have u32 chrono_stat[3]; - should probably be [__TCP_CHRONO_MAX - 1] (or - CHRONO_FIRST which is defined to be 1). Checking if (old != 0) would make the code more readable. David
From: Arnd Bergmann <arnd@arndb.de> Date: Fri, 28 Jul 2017 16:41:37 +0200 > 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 <arnd@arndb.de> Applied, thanks Arnd.
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 886d874775df..bb901297a369 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; }
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 <arnd@arndb.de> --- net/ipv4/tcp_output.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)