[src/trunk]: src/lib/libc/resolv kqueue(2) file descriptors are not inherited...

[christos <christos%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/d260abbd7630
branches:  trunk
changeset: 1023886:d260abbd7630
user:      christos <christos%NetBSD.org@localhost>
date:      Thu Sep 30 12:35:55 2021 +0000

description:
kqueue(2) file descriptors are not inherited across fork(2). A
process that that calls getaddrinfo(3) will end up cacheing the
kqueue(2) file descriptor in its res_state structure. If that
process fork(2)s and calls getaddrinfo(3) again might end up closing
that cached file descriptor which can end up pointing to a different
file object than the kqueue(2) original one. To fix this, associate
the kqueue(2) file descriptor with the process id that created it,
and don't close(2) it if it is being closed from a different process.
An alternative fix would be to attach the resolver to a fork(2) hook
to cleanup the res_state, but handling it internally in the resolver
is less intrusive. This was discovered by Dima Veselov when using
the FreeRADIUS package.

diffstat:

 lib/libc/resolv/res_init.c    |  42 ++++++++++++++++++++++++++++--------------
 lib/libc/resolv/res_private.h |   3 ++-
 2 files changed, 30 insertions(+), 15 deletions(-)

diffs (109 lines):

diff -r 597b50af93e7 -r d260abbd7630 lib/libc/resolv/res_init.c
--- a/lib/libc/resolv/res_init.c        Thu Sep 30 10:19:52 2021 +0000
+++ b/lib/libc/resolv/res_init.c        Thu Sep 30 12:35:55 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: res_init.c,v 1.31 2017/04/19 22:21:07 christos Exp $   */
+/*     $NetBSD: res_init.c,v 1.32 2021/09/30 12:35:55 christos Exp $   */
 
 /*
  * Copyright (c) 1985, 1989, 1993
@@ -72,7 +72,7 @@
 static const char sccsid[] = "@(#)res_init.c   8.1 (Berkeley) 6/7/93";
 static const char rcsid[] = "Id: res_init.c,v 1.26 2008/12/11 09:59:00 marka Exp";
 #else
-__RCSID("$NetBSD: res_init.c,v 1.31 2017/04/19 22:21:07 christos Exp $");
+__RCSID("$NetBSD: res_init.c,v 1.32 2021/09/30 12:35:55 christos Exp $");
 #endif
 #endif /* LIBC_SCCS and not lint */
 
@@ -190,6 +190,21 @@
        return (__res_vinit(statp, 0));
 }
 
+static int
+__res_kqinit(res_state statp)
+{
+       struct kevent kc;
+       struct __res_state_ext *ext = statp->_u._ext.ext;
+
+       ext->kq = kqueue1(O_CLOEXEC);
+       ext->kqpid = getpid();
+       EV_SET(&kc, ext->resfd, EVFILT_VNODE,
+           EV_ADD|EV_ENABLE|EV_CLEAR, NOTE_DELETE|NOTE_WRITE| NOTE_EXTEND|
+           NOTE_ATTRIB|NOTE_LINK|NOTE_RENAME|NOTE_REVOKE, 0, 0);
+       (void)kevent(ext->kq, &kc, 1, NULL, 0, &ts);
+       return ext->kq;
+}
+
 /*% This function has to be reachable by res_data.c but not publically. */
 int
 __res_vinit(res_state statp, int preinit) {
@@ -346,7 +361,6 @@
        nserv = 0;
        if ((fp = fopen(__res_conf_name, "re")) != NULL) {
            struct stat st;
-           struct kevent kc;
 
            /* read the config file */
            while (fgets(buf, (int)sizeof(buf), fp) != NULL) {
@@ -500,11 +514,7 @@
            if (fstat(statp->_u._ext.ext->resfd, &st) != -1)
                    __res_conf_time = statp->_u._ext.ext->res_conf_time =
                        st.st_mtimespec;
-           statp->_u._ext.ext->kq = kqueue1(O_CLOEXEC);
-           EV_SET(&kc, statp->_u._ext.ext->resfd, EVFILT_VNODE,
-               EV_ADD|EV_ENABLE|EV_CLEAR, NOTE_DELETE|NOTE_WRITE| NOTE_EXTEND|
-               NOTE_ATTRIB|NOTE_LINK|NOTE_RENAME|NOTE_REVOKE, 0, 0);
-           (void)kevent(statp->_u._ext.ext->kq, &kc, 1, NULL, 0, &ts);
+           __res_kqinit(statp);
        } else {
            statp->_u._ext.ext->kq = -1;
            statp->_u._ext.ext->resfd = -1;
@@ -573,6 +583,9 @@
                struct kevent ke;
                if (statp->_u._ext.ext->kq == -1)
                        goto out;
+               if (statp->_u._ext.ext->kqpid != getpid() &&
+                   __res_kqinit(statp) == -1)
+                       goto out;
 
                switch (kevent(statp->_u._ext.ext->kq, NULL, 0, &ke, 1, &ts)) {
                case 0:
@@ -812,13 +825,14 @@
 void
 res_ndestroy(res_state statp)
 {
+       struct __res_state_ext *ext = statp->_u._ext.ext;
        res_nclose(statp);
-       if (statp->_u._ext.ext != NULL) {
-               if (statp->_u._ext.ext->kq != -1)
-                       (void)close(statp->_u._ext.ext->kq);
-               if (statp->_u._ext.ext->resfd != -1)
-                       (void)close(statp->_u._ext.ext->resfd);
-               free(statp->_u._ext.ext);
+       if (ext != NULL) {
+               if (ext->kq != -1 && ext->kqpid == getpid())
+                       (void)close(ext->kq);
+               if (ext->resfd != -1)
+                       (void)close(ext->resfd);
+               free(ext);
                statp->_u._ext.ext = NULL;
        }
        if (statp->_rnd != NULL) {
diff -r 597b50af93e7 -r d260abbd7630 lib/libc/resolv/res_private.h
--- a/lib/libc/resolv/res_private.h     Thu Sep 30 10:19:52 2021 +0000
+++ b/lib/libc/resolv/res_private.h     Thu Sep 30 12:35:55 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: res_private.h,v 1.3 2009/10/24 17:24:01 christos Exp $ */
+/*     $NetBSD: res_private.h,v 1.4 2021/09/30 12:35:55 christos Exp $ */
 
 #ifndef res_private_h
 #define res_private_h
@@ -16,6 +16,7 @@
        char nsuffix2[64];
        struct timespec res_conf_time;
        int kq, resfd;
+       pid_t kqpid;
 };
 
 extern int res_ourserver_p(const res_state, const struct sockaddr *);