From 2683e267fa6c20d2e7a498a85f79a1dfc4301f23 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Mon, 26 Oct 2015 18:42:22 -0400 Subject: [PATCH] safely handle failure to open hosts, services, resolv.conf files previously, transient failures like fd exhaustion or other resource-related errors were treated the same as non-existence of these files, leading to fallbacks or false-negative results. in particular: - failure to open hosts resulted in fallback to dns, possibly yielding EAI_NONAME for a hostname that should be defined locally, or an unwanted result from dns that the hosts file was intended to replace. - failure to open services resulted in EAI_SERVICE. - failure to open resolv.conf resulted in querying localhost rather than the configured nameservers. now, only permanent errors trigger the fallback behaviors above; all other errors are reportable to the caller as EAI_SYSTEM. --- src/network/lookup_name.c | 10 +++++++++- src/network/lookup_serv.c | 10 +++++++++- src/network/res_msend.c | 13 +++++++++++-- 3 files changed, 29 insertions(+), 4 deletions(-) diff --git a/src/network/lookup_name.c b/src/network/lookup_name.c index 0225a934..df9e623e 100644 --- a/src/network/lookup_name.c +++ b/src/network/lookup_name.c @@ -9,6 +9,7 @@ #include #include #include +#include #include "lookup.h" #include "stdio_impl.h" #include "syscall.h" @@ -51,7 +52,14 @@ static int name_from_hosts(struct address buf[static MAXADDRS], char canon[stati int cnt = 0; unsigned char _buf[1032]; FILE _f, *f = __fopen_rb_ca("/etc/hosts", &_f, _buf, sizeof _buf); - if (!f) return 0; + if (!f) switch (errno) { + case ENOENT: + case ENOTDIR: + case EACCES: + return 0; + default: + return EAI_SYSTEM; + } while (fgets(line, sizeof line, f) && cnt < MAXADDRS) { char *p, *z; diff --git a/src/network/lookup_serv.c b/src/network/lookup_serv.c index 4faa5bc7..66ebaea2 100644 --- a/src/network/lookup_serv.c +++ b/src/network/lookup_serv.c @@ -4,6 +4,7 @@ #include #include #include +#include #include "lookup.h" #include "stdio_impl.h" @@ -69,7 +70,14 @@ int __lookup_serv(struct service buf[static MAXSERVS], const char *name, int pro unsigned char _buf[1032]; FILE _f, *f = __fopen_rb_ca("/etc/services", &_f, _buf, sizeof _buf); - if (!f) return EAI_SERVICE; + if (!f) switch (errno) { + case ENOENT: + case ENOTDIR: + case EACCES: + return EAI_SERVICE; + default: + return EAI_SYSTEM; + } while (fgets(line, sizeof line, f) && cnt < MAXSERVS) { if ((p=strchr(line, '#'))) *p++='\n', *p=0; diff --git a/src/network/res_msend.c b/src/network/res_msend.c index 35f106dd..d0e8e481 100644 --- a/src/network/res_msend.c +++ b/src/network/res_msend.c @@ -54,7 +54,15 @@ int __res_msend(int nqueries, const unsigned char *const *queries, /* Get nameservers from resolv.conf, fallback to localhost */ f = __fopen_rb_ca("/etc/resolv.conf", &_f, _buf, sizeof _buf); - if (f) for (nns=0; nns<3 && fgets(line, sizeof line, f); ) { + if (!f) switch (errno) { + case ENOENT: + case ENOTDIR: + case EACCES: + goto no_resolv_conf; + default: + return -1; + } + for (nns=0; nns<3 && fgets(line, sizeof line, f); ) { if (!strncmp(line, "options", 7) && isspace(line[7])) { unsigned long x; char *p, *z; @@ -92,7 +100,8 @@ int __res_msend(int nqueries, const unsigned char *const *queries, } } } - if (f) __fclose_ca(f); + __fclose_ca(f); +no_resolv_conf: if (!nns) { ns[0].sin.sin_family = AF_INET; ns[0].sin.sin_port = htons(53); -- 2.25.1