From 2115fcc1e673079fe76e949ac0904267075c25a4 Mon Sep 17 00:00:00 2001

From: Lennart Poettering <lennart@poettering.net>

Date: Wed, 31 Oct 2018 13:04:20 +0100

Subject: [PATCH] nspawn: beef up netns checking a bit, for compat with old

 kernels

Fixes: #10544

Cherry-picked from: 6619ad889da260cf83079cc74a85d571acd1df5a

---

 src/basic/stat-util.c     | 40 +++++++++++++++++++++++++++++++++++----

 src/nspawn/nspawn.c       |  8 +++++---

 src/test/test-stat-util.c | 15 +++++++++++++++

 3 files changed, 56 insertions(+), 7 deletions(-)

diff --git a/src/basic/stat-util.c b/src/basic/stat-util.c

index 07154e25b..26aee9bad 100644

--- a/src/basic/stat-util.c

+++ b/src/basic/stat-util.c

@@ -204,15 +204,47 @@ int fd_is_network_fs(int fd) {

 }

 int fd_is_network_ns(int fd) {

+        struct statfs s;

         int r;

-        r = fd_is_fs_type(fd, NSFS_MAGIC);

-        if (r <= 0)

-                return r;

+        /* Checks whether the specified file descriptor refers to a network namespace. On old kernels there's no nice

+         * way to detect that, hence on those we'll return a recognizable error (EUCLEAN), so that callers can handle

+         * this somewhat nicely.

+         *

+         * This function returns > 0 if the fd definitely refers to a network namespace, 0 if it definitely does not

+         * refer to a network namespace, -EUCLEAN if we can't determine, and other negative error codes on error. */

+

+        if (fstatfs(fd, &s) < 0)

+                return -errno;

+

+        if (!is_fs_type(&s, NSFS_MAGIC)) {

+                /* On really old kernels, there was no "nsfs", and network namespace sockets belonged to procfs

+                 * instead. Handle that in a somewhat smart way. */

+

+                if (is_fs_type(&s, PROC_SUPER_MAGIC)) {

+                        struct statfs t;

+

+                        /* OK, so it is procfs. Let's see if our own network namespace is procfs, too. If so, then the

+                         * passed fd might refer to a network namespace, but we can't know for sure. In that case,

+                         * return a recognizable error. */

+

+                        if (statfs("/proc/self/ns/net", &t) < 0)

+                                return -errno;

+

+                        if (s.f_type == t.f_type)

+                                return -EUCLEAN; /* It's possible, we simply don't know */

+                }

+

+                return 0; /* No! */

+        }

         r = ioctl(fd, NS_GET_NSTYPE);

-        if (r < 0)

+        if (r < 0) {

+                if (errno == ENOTTY) /* Old kernels didn't know this ioctl, let's also return a recognizable error in that case */

+                        return -EUCLEAN;

+

                 return -errno;

+        }

         return r == CLONE_NEWNET;

 }

diff --git a/src/nspawn/nspawn.c b/src/nspawn/nspawn.c

index 56877bd93..8aec893a6 100644

--- a/src/nspawn/nspawn.c

+++ b/src/nspawn/nspawn.c

@@ -3701,10 +3701,12 @@ static int run(int master,

                         return log_error_errno(errno, "Cannot open file %s: %m", arg_network_namespace_path);

                 r = fd_is_network_ns(netns_fd);

-                if (r < 0 && r != -ENOTTY)

+                if (r == -EUCLEAN)

+                        log_debug_errno(r, "Cannot determine if passed network namespace path '%s' really refers to a network namespace, assuming it does.", arg_network_namespace_path);

+                else if (r < 0)

                         return log_error_errno(r, "Failed to check %s fs type: %m", arg_network_namespace_path);

-                if (r == 0) {

-                        log_error("Path %s doesn't refer to a network namespace", arg_network_namespace_path);

+                else if (r == 0) {

+                        log_error("Path %s doesn't refer to a network namespace, refusing.", arg_network_namespace_path);

                         return -EINVAL;

                 }

         }

diff --git a/src/test/test-stat-util.c b/src/test/test-stat-util.c

index 43f56a6c2..2b0564d8a 100644

--- a/src/test/test-stat-util.c

+++ b/src/test/test-stat-util.c

@@ -67,11 +67,26 @@ static void test_path_is_temporary_fs(void) {

         assert_se(path_is_temporary_fs("/i-dont-exist") == -ENOENT);

 }

+static void test_fd_is_network_ns(void) {

+        _cleanup_close_ int fd = -1;

+        assert_se(fd_is_network_ns(STDIN_FILENO) == 0);

+        assert_se(fd_is_network_ns(STDERR_FILENO) == 0);

+        assert_se(fd_is_network_ns(STDOUT_FILENO) == 0);

+

+        assert_se((fd = open("/proc/self/ns/mnt", O_CLOEXEC|O_RDONLY)) >= 0);

+        assert_se(IN_SET(fd_is_network_ns(fd), 0, -EUCLEAN));

+        fd = safe_close(fd);

+

+        assert_se((fd = open("/proc/self/ns/net", O_CLOEXEC|O_RDONLY)) >= 0);

+        assert_se(IN_SET(fd_is_network_ns(fd), 1, -EUCLEAN));

+}

+

 int main(int argc, char *argv[]) {

         test_files_same();

         test_is_symlink();

         test_path_is_fs_type();

         test_path_is_temporary_fs();

+        test_fd_is_network_ns();

         return 0;

 }