From 77a6d976aa4571427ba832226a3232f92bfd169f Mon Sep 17 00:00:00 2001 From: Stefano Brivio Date: Thu, 16 Feb 2023 01:53:30 +0100 Subject: [PATCH] dhcp: Fix netmask calculation for option 1 from prefix length Similar to the conf_print() fix from commit 4129764ecaeb ("conf: Fix mask calculation from prefix_len in conf_print()"): to calculate an IPv4 netmask from the prefix length, we need to left shift 32 all-one bits by 32 minus the prefix length -- not by the prefix length itself. Reported-by: Yalan Zhang Fixes: dd09cceaee21 ("Minor improvements to IPv4 netmask handling") Signed-off-by: Stefano Brivio Reviewed-by: David Gibson --- dhcp.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/dhcp.c b/dhcp.c index 6088886..edab780 100644 --- a/dhcp.c +++ b/dhcp.c @@ -335,7 +335,7 @@ int dhcp(const struct ctx *c, const struct pool *p) m->chaddr[3], m->chaddr[4], m->chaddr[5]); m->yiaddr = c->ip4.addr; - mask.s_addr = htonl(0xffffffff << c->ip4.prefix_len); + mask.s_addr = htonl(0xffffffff << (32 - c->ip4.prefix_len)); memcpy(opts[1].s, &mask, sizeof(mask)); memcpy(opts[3].s, &c->ip4.gw, sizeof(c->ip4.gw)); memcpy(opts[54].s, &c->ip4.gw, sizeof(c->ip4.gw));