From 85050ac5a2677a8ebf2722e93b5c037ec675c036 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Mon, 19 Sep 2022 20:10:10 -0400 Subject: getaddrinfo: add EAI_NODATA error code to distinguish NODATA vs NxDomain this was apparently omitted long ago out of a lack of understanding of its importance and the fact that POSIX doesn't specify it. despite not being officially standardized, however, it turns out that at least AIX, glibc, NetBSD, OpenBSD, QNX, and Solaris document and support it. in certain usage cases, such as implementing a DNS gateway on top of the stub resolver interfaces, it's necessary to distinguish the case where a name does not exit (NxDomain) from one where it exists but has no addresses (or other records) of the requested type (NODATA). in fact, even the legacy gethostbyname API had this distinction, which we were previously unable to support correctly because the backend lacked it. apart from fixing an important functionality gap, adding this distinction helps clarify to users how search domain fallback works (falling back in cases corresponding to EAI_NONAME, not in ones corresponding to EAI_NODATA), a topic that has been a source of ongoing confusion and frustration. as a result of this change, EAI_NONAME is no longer a valid universal error code for getaddrinfo in the case where AI_ADDRCONFIG has suppressed use of all address families. in order to return an accurate result in this case, getaddrinfo is modified to still perform at least one lookup. this will almost surely fail (with a network error, since there is no v4 or v6 network to query DNS over) unless a result comes from the hosts file or from ip literal parsing, but in case it does succeed, the result is replaced by EAI_NODATA. glibc has a related error code, EAI_ADDRFAMILY, that could be used for the AI_ADDRCONFIG case and certain NODATA cases, but distinguishing them properly in full generality seems to require additional DNS queries that are otherwise not useful. on glibc, it is only used for ip literals with mismatching family, not for DNS or hosts file results where the name has addresses only in the opposite family. since this seems misleading and inconsistent, and since EAI_NODATA already covers the semantic case where the "name" exists but doesn't have any addresses in the requested family, we do not adopt EAI_ADDRFAMILY at this time. this could be changed at some point if desired, but the logic for getting all the corner cases with AI_ADDRCONFIG right is slightly nontrivial. --- include/netdb.h | 1 + src/network/gai_strerror.c | 2 +- src/network/getaddrinfo.c | 5 ++++- src/network/gethostbyname2_r.c | 3 +++ src/network/lookup_ipliteral.c | 4 ++-- src/network/lookup_name.c | 4 ++-- 6 files changed, 13 insertions(+), 6 deletions(-) diff --git a/include/netdb.h b/include/netdb.h index d096c781..3af065e2 100644 --- a/include/netdb.h +++ b/include/netdb.h @@ -44,6 +44,7 @@ struct addrinfo { #define EAI_NONAME -2 #define EAI_AGAIN -3 #define EAI_FAIL -4 +#define EAI_NODATA -5 #define EAI_FAMILY -6 #define EAI_SOCKTYPE -7 #define EAI_SERVICE -8 diff --git a/src/network/gai_strerror.c b/src/network/gai_strerror.c index 9596580e..56b71503 100644 --- a/src/network/gai_strerror.c +++ b/src/network/gai_strerror.c @@ -6,7 +6,7 @@ static const char msgs[] = "Name does not resolve\0" "Try again\0" "Non-recoverable error\0" - "Unknown error\0" + "Name has no usable address\0" "Unrecognized address family or invalid length\0" "Unrecognized socket type\0" "Unrecognized service\0" diff --git a/src/network/getaddrinfo.c b/src/network/getaddrinfo.c index 9df045f6..64ad259a 100644 --- a/src/network/getaddrinfo.c +++ b/src/network/getaddrinfo.c @@ -16,6 +16,7 @@ int getaddrinfo(const char *restrict host, const char *restrict serv, const stru char canon[256], *outcanon; int nservs, naddrs, nais, canon_len, i, j, k; int family = AF_UNSPEC, flags = 0, proto = 0, socktype = 0; + int no_family = 0; struct aibuf *out; if (!host && !serv) return EAI_NONAME; @@ -82,7 +83,7 @@ int getaddrinfo(const char *restrict host, const char *restrict serv, const stru default: return EAI_SYSTEM; } - if (family == tf[i]) return EAI_NONAME; + if (family == tf[i]) no_family = 1; family = tf[1-i]; } } @@ -93,6 +94,8 @@ int getaddrinfo(const char *restrict host, const char *restrict serv, const stru naddrs = __lookup_name(addrs, canon, host, family, flags); if (naddrs < 0) return naddrs; + if (no_family) return EAI_NODATA; + nais = nservs * naddrs; canon_len = strlen(canon); out = calloc(1, nais * sizeof(*out) + canon_len + 1); diff --git a/src/network/gethostbyname2_r.c b/src/network/gethostbyname2_r.c index c9f3acc4..a5eb67fe 100644 --- a/src/network/gethostbyname2_r.c +++ b/src/network/gethostbyname2_r.c @@ -23,6 +23,9 @@ int gethostbyname2_r(const char *name, int af, case EAI_NONAME: *err = HOST_NOT_FOUND; return 0; + case EAI_NODATA: + *err = NO_DATA; + return 0; case EAI_AGAIN: *err = TRY_AGAIN; return EAGAIN; diff --git a/src/network/lookup_ipliteral.c b/src/network/lookup_ipliteral.c index 2fddab73..1e766206 100644 --- a/src/network/lookup_ipliteral.c +++ b/src/network/lookup_ipliteral.c @@ -15,7 +15,7 @@ int __lookup_ipliteral(struct address buf[static 1], const char *name, int famil struct in6_addr a6; if (__inet_aton(name, &a4) > 0) { if (family == AF_INET6) /* wrong family */ - return EAI_NONAME; + return EAI_NODATA; memcpy(&buf[0].addr, &a4, sizeof a4); buf[0].family = AF_INET; buf[0].scopeid = 0; @@ -34,7 +34,7 @@ int __lookup_ipliteral(struct address buf[static 1], const char *name, int famil if (inet_pton(AF_INET6, name, &a6) <= 0) return 0; if (family == AF_INET) /* wrong family */ - return EAI_NONAME; + return EAI_NODATA; memcpy(&buf[0].addr, &a6, sizeof a6); buf[0].family = AF_INET6; diff --git a/src/network/lookup_name.c b/src/network/lookup_name.c index bec6ba22..37d481f9 100644 --- a/src/network/lookup_name.c +++ b/src/network/lookup_name.c @@ -79,7 +79,7 @@ static int name_from_hosts(struct address buf[static MAXADDRS], char canon[stati case 0: continue; default: - badfam = EAI_NONAME; + badfam = EAI_NODATA; break; } @@ -175,7 +175,7 @@ static int name_from_dns(struct address buf[static MAXADDRS], char canon[static __dns_parse(abuf[i], alens[i], dns_parse_callback, &ctx); if (ctx.cnt) return ctx.cnt; - return EAI_NONAME; + return EAI_NODATA; } static int name_from_dns_search(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family) -- cgit v1.2.3-70-g09d2