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resolved: fix a minimal race, when reading /etc/resolv.conf

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The user might replace a foreign /etc/resolv.conf with a symlink to one
of ours between the time we did stat() and open the file. Hence, let's
check the fstat() data right after opening the file, a second time.
This commit is contained in:
Lennart Poettering 2017-12-08 16:51:46 +01:00
parent 848f01784e
commit 043d392878
1 changed files with 25 additions and 11 deletions
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36
src/resolve/resolved-resolv-conf.c
View file

@ -32,9 +32,29 @@
#include "string-util.h"
#include "strv.h"
static bool file_is_our_own(const struct stat *st) {
struct stat own1, own2;
assert(st);
/* Is it symlinked to our own file? */
if (stat(PRIVATE_UPLINK_RESOLV_CONF, &own1) >= 0 &&
st->st_dev == own1.st_dev &&
st->st_ino == own1.st_ino)
return true;
/* Is it symlinked to our own stub file? */
if (stat(PRIVATE_STUB_RESOLV_CONF, &own2) >= 0 &&
st->st_dev == own2.st_dev &&
st->st_ino == own2.st_ino)
return true;
return false;
}
int manager_read_resolv_conf(Manager *m) {
_cleanup_fclose_ FILE *f = NULL;
struct stat st, own;
struct stat st;
char line[LINE_MAX];
usec_t t;
int r;
@ -61,16 +81,7 @@ int manager_read_resolv_conf(Manager *m) {
if (t == m->resolv_conf_mtime)
return 0;
/* Is it symlinked to our own file? */
if (stat(PRIVATE_UPLINK_RESOLV_CONF, &own) >= 0 &&
st.st_dev == own.st_dev &&
st.st_ino == own.st_ino)
return 0;
/* Is it symlinked to our own stub file? */
if (stat(PRIVATE_STUB_RESOLV_CONF, &own) >= 0 &&
st.st_dev == own.st_dev &&
st.st_ino == own.st_ino)
if (file_is_our_own(&st))
return 0;
f = fopen("/etc/resolv.conf", "re");
@ -87,6 +98,9 @@ int manager_read_resolv_conf(Manager *m) {
goto clear;
}
if (file_is_our_own(&st))
return 0;
dns_server_mark_all(m->dns_servers);
dns_search_domain_mark_all(m->search_domains);