>From a6244de1c94588cd8cc965c15619d2649418f7a3 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Wed, 30 Jul 2025 09:32:02 -0400 Subject: [PATCH] fix erroneous definition of IN6_IS_ADDR_V4COMPAT v4-compatible addresses in ipv6 are a deprecated feature where the high 96 bits are all zero and an ipv4 address is stored in the low 32 bits. however, since :: and ::1 are the unspecified and loopback addresses, these two particular values are excluded from the definition of the v4-compat class. our version of the macro incorrectly assessed this condition by checking only the high 96 and low 8 bits. this incorrectly excluded the v4compat version of any ipv4 address ending in .1, not just ::1. rather than writing out non-obvious or error-prone conditions on the individual address bytes, just express the "not :: or ::1" condition naturally using the existing IN6_IS_ADDR_UNSPECIFIED and IN6_IS_ADDR_LOOPBACK macros, after checking that the high 96 bits are all zero. any vaguely reasonable compiler will collapse out the redundant tests of the upper bits as part of CSE. --- include/netinet/in.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/include/netinet/in.h b/include/netinet/in.h index fb628b61..60bbaa75 100644 --- a/include/netinet/in.h +++ b/include/netinet/in.h @@ -132,7 +132,8 @@ uint16_t ntohs(uint16_t); #define IN6_IS_ADDR_V4COMPAT(a) \ (((uint32_t *) (a))[0] == 0 && ((uint32_t *) (a))[1] == 0 && \ - ((uint32_t *) (a))[2] == 0 && ((uint8_t *) (a))[15] > 1) + ((uint32_t *) (a))[2] == 0 && \ + !IN6_IS_ADDR_UNSPECIFIED(a) && !IN6_IS_ADDR_LOOPBACK(a)) #define IN6_IS_ADDR_MC_NODELOCAL(a) \ (IN6_IS_ADDR_MULTICAST(a) && ((((uint8_t *) (a))[1] & 0xf) == 0x1)) -- 2.21.0