Implement bind mount to overwrite /etc/resolv.conf instead of the current method of rename followed by copy. The bind mount method works even if the file is designated as immutable Signed-off-by: Srihari Parimi <sparimi(a)redhat.com&gt; --- daemon/sh.c | 86 ++++++++++++++++++++++------------------------------- 1 file changed, 35 insertions(+), 51 deletions(-) diff --git a/daemon/sh.c b/daemon/sh.c index 74e003410..aab9a4534 100644 --- a/daemon/sh.c +++ b/daemon/sh.c @@ -150,8 +150,9 @@ free_bind_state (struct bind_state *bs) static int set_up_etc_resolv_conf (struct resolver_state *rs) { + char *src_etc_resolv = "/etc/resolv.conf"; struct stat statbuf; - CLEANUP_FREE char *buf = NULL; + int r, fd = -1; rs->sysroot_etc_resolv_conf_old = NULL; @@ -161,50 +162,43 @@ set_up_etc_resolv_conf (struct resolver_state *rs) reply_with_perror ("malloc"); goto error; } - - /* If /etc/resolv.conf exists, rename it to the backup file. Note - * that on Ubuntu it's a dangling symlink. + /* If /sysroot/etc/resolv.conf does not exist, create one for mount + * bind to succeed. lstat() call handles dnagling links */ - if (lstat (rs->sysroot_etc_resolv_conf, &statbuf) == 0) { - /* Make a random name for the backup file. */ - if (asprintf (&buf, "%s/etc/XXXXXXXX", sysroot) == -1) { - reply_with_perror ("asprintf"); - goto error; - } - if (random_name (buf) == -1) { - reply_with_perror ("random_name"); - goto error; - } - rs->sysroot_etc_resolv_conf_old = strdup (buf); - if (!rs->sysroot_etc_resolv_conf_old) { - reply_with_perror ("strdup"); - goto error; + if (lstat (rs->sysroot_etc_resolv_conf, &statbuf) != 0) { + if (errno != ENOENT) { + reply_with_perror ("lstat: %s", rs->sysroot_etc_resolv_conf); + return -1; } - - if (verbose) - fprintf (stderr, "renaming %s to %s\n", rs->sysroot_etc_resolv_conf, - rs->sysroot_etc_resolv_conf_old); - - if (rename (rs->sysroot_etc_resolv_conf, - rs->sysroot_etc_resolv_conf_old) == -1) { - reply_with_perror ("rename: %s to %s", rs->sysroot_etc_resolv_conf, - rs->sysroot_etc_resolv_conf_old); - goto error; + /* create empty file */ + fd = open (rs->sysroot_etc_resolv_conf, + O_WRONLY|O_CREAT|O_NOCTTY|O_CLOEXEC, 0644); + if (fd == -1) { + reply_with_perror ("open: %s", rs->sysroot_etc_resolv_conf); + return -1; } + close(fd); } - - /* Now that the guest's <sysroot>/etc/resolv.conf is out the way, we - * can create our own copy of the appliance /etc/resolv.conf. - */ - ignore_value (command (NULL, NULL, "cp", "/etc/resolv.conf", - rs->sysroot_etc_resolv_conf, NULL)); - + if (verbose) + fprintf (stderr, "mount %s to %s\n", src_etc_resolv, + rs->sysroot_etc_resolv_conf); + /* mount bind read only */ + r = command (NULL, NULL, "mount", "--bind", "-o ro", src_etc_resolv, + rs->sysroot_etc_resolv_conf, NULL); + if (r == -1) { + reply_with_perror ("mount: %s to %s failed\n", + src_etc_resolv, rs->sysroot_etc_resolv_conf); + goto error; + } + if (verbose) + fprintf (stderr, "mount %s to %s done\n", src_etc_resolv, + rs->sysroot_etc_resolv_conf); rs->mounted = true; + return 0; - error: +error: free (rs->sysroot_etc_resolv_conf); - free (rs->sysroot_etc_resolv_conf_old); return -1; } @@ -212,20 +206,10 @@ static void free_resolver_state (struct resolver_state *rs) { if (rs->mounted) { - unlink (rs->sysroot_etc_resolv_conf); - - if (rs->sysroot_etc_resolv_conf_old) { - if (verbose) - fprintf (stderr, "renaming %s to %s\n", rs->sysroot_etc_resolv_conf_old, - rs->sysroot_etc_resolv_conf); - - if (rename (rs->sysroot_etc_resolv_conf_old, - rs->sysroot_etc_resolv_conf) == -1) - perror ("error: could not restore /etc/resolv.conf"); - - free (rs->sysroot_etc_resolv_conf_old); - } - + /* umount sysroot_etc_resolv_conf */ + if (verbose) + fprintf (stderr, "umount %s\n", rs->sysroot_etc_resolv_conf); + umount_ignore_fail(rs->sysroot_etc_resolv_conf); free (rs->sysroot_etc_resolv_conf); rs->mounted = false; } -- 2.52.0