From d6df198d924775e4751561cf60ef0294e95f74df Mon Sep 17 00:00:00 2001 From: Phil Sutter Date: Tue, 1 Dec 2015 22:45:15 +0100 Subject: [PATCH] net: ipv6: restrict hop_limit sysctl setting to range [1; 255] Setting a value bigger than 255 resulted in using only the lower eight bits of that value as it is assigned to the u8 header field. To avoid this unexpected result, reject such values. Setting a value of zero is technically possible, but hosts receiving such a packet have to treat it like hop_limit was set to one, according to RFC2460. Therefore I don't see a use-case for that. Setting a route's hop_limit to zero in iproute2 means to use the sysctl default, which is not the case here: Setting e.g. net.conf.eth0.hop_limit=0 will not make the kernel use net.conf.all.hop_limit for outgoing packets on eth0. To avoid these kinds of confusion, reject zero. Signed-off-by: Phil Sutter Signed-off-by: David S. Miller --- net/ipv6/addrconf.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index d84742f003a9..a5de1a616c12 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -5199,6 +5199,20 @@ int addrconf_sysctl_forward(struct ctl_table *ctl, int write, return ret; } +static +int addrconf_sysctl_hop_limit(struct ctl_table *ctl, int write, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + struct ctl_table lctl; + int min_hl = 1, max_hl = 255; + + lctl = *ctl; + lctl.extra1 = &min_hl; + lctl.extra2 = &max_hl; + + return proc_dointvec_minmax(&lctl, write, buffer, lenp, ppos); +} + static int addrconf_sysctl_mtu(struct ctl_table *ctl, int write, void __user *buffer, size_t *lenp, loff_t *ppos) @@ -5454,7 +5468,7 @@ static struct addrconf_sysctl_table .data = &ipv6_devconf.hop_limit, .maxlen = sizeof(int), .mode = 0644, - .proc_handler = proc_dointvec, + .proc_handler = addrconf_sysctl_hop_limit, }, { .procname = "mtu", -- 2.20.1