tcp: restrict net.ipv4.tcp_adv_win_scale (#20312)
tcp_win_from_space() does the following:
if (sysctl_tcp_adv_win_scale <= 0)
return space >> (-sysctl_tcp_adv_win_scale);
else
return space - (space >> sysctl_tcp_adv_win_scale);
"space" is int.
As per C99 6.5.7 (3) shifting int for 32 or more bits is
undefined behaviour.
Indeed, if sysctl_tcp_adv_win_scale is exactly 32,
space >> 32 equals space and function returns 0.
Which means we busyloop in tcp_fixup_rcvbuf().
Restrict net.ipv4.tcp_adv_win_scale to [-31, 31].
Fix https://bugzilla.kernel.org/show_bug.cgi?id=20312
Steps to reproduce:
echo 32 >/proc/sys/net/ipv4/tcp_adv_win_scale
wget www.kernel.org
[softlockup]
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index e91911d..1b4ec21 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -26,6 +26,8 @@
static int tcp_retr1_max = 255;
static int ip_local_port_range_min[] = { 1, 1 };
static int ip_local_port_range_max[] = { 65535, 65535 };
+static int tcp_adv_win_scale_min = -31;
+static int tcp_adv_win_scale_max = 31;
/* Update system visible IP port range */
static void set_local_port_range(int range[2])
@@ -426,7 +428,9 @@
.data = &sysctl_tcp_adv_win_scale,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = proc_dointvec
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &tcp_adv_win_scale_min,
+ .extra2 = &tcp_adv_win_scale_max,
},
{
.procname = "tcp_tw_reuse",