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From 2683e267fa6c20d2e7a498a85f79a1dfc4301f23 Mon Sep 17 00:00:00 2001
From: Rich Felker <dalias@aerifal.cx>
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 0225a93..df9e623 100644
--- a/src/network/lookup_name.c
+++ b/src/network/lookup_name.c
@@ -9,6 +9,7 @@
#include <fcntl.h>
#include <unistd.h>
#include <pthread.h>
+#include <errno.h>
#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 4faa5bc..66ebaea 100644
--- a/src/network/lookup_serv.c
+++ b/src/network/lookup_serv.c
@@ -4,6 +4,7 @@
#include <ctype.h>
#include <string.h>
#include <fcntl.h>
+#include <errno.h>
#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 35f106d..d0e8e48 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);
--
2.7.0
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