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nspawn: refuse politely when we are run in the non-host netns in combination with --image=

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Strictly speaking this doesn't really fix #15079, but it at least means
we won't hang anymore.

Fixes: #15079
This commit is contained in:
Lennart Poettering 2020-04-22 17:12:35 +02:00
parent 1433e0f212
commit 287b737693
1 changed files with 56 additions and 0 deletions
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56
src/nspawn/nspawn.c
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@ -4820,6 +4820,58 @@ static int initialize_rlimits(void) {
return 0;
}
static int cant_be_in_netns(void) {
union sockaddr_union sa = {
.un = {
.sun_family = AF_UNIX,
.sun_path = "/run/udev/control",
},
};
char udev_path[STRLEN("/proc//ns/net") + DECIMAL_STR_MAX(pid_t)];
_cleanup_free_ char *udev_ns = NULL, *our_ns = NULL;
_cleanup_close_ int fd = -1;
struct ucred ucred;
int r;
/* Check if we are in the same netns as udev. If we aren't, then device monitoring (and thus waiting
* for loopback block devices) won't work, and we will hang. Detect this case and exit early with a
* nice message. */
if (!arg_image) /* only matters if --image= us used, i.e. we actually need to use loopback devices */
return 0;
fd = socket(AF_UNIX, SOCK_SEQPACKET|SOCK_NONBLOCK|SOCK_CLOEXEC, 0);
if (fd < 0)
return log_error_errno(errno, "Failed to allocate udev control socket: %m");
if (connect(fd, &sa.un, SOCKADDR_UN_LEN(sa.un)) < 0) {
if (errno == ENOENT || ERRNO_IS_DISCONNECT(errno))
return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP),
"Sorry, but --image= requires access to the host's /run/ hierarchy, since we need access to udev.");
return log_error_errno(errno, "Failed to connect socket to udev control socket: %m");
}
r = getpeercred(fd, &ucred);
if (r < 0)
return log_error_errno(r, "Failed to determine peer of udev control socket: %m");
xsprintf(udev_path, "/proc/" PID_FMT "/ns/net", ucred.pid);
r = readlink_malloc(udev_path, &udev_ns);
if (r < 0)
return log_error_errno(r, "Failed to read network namespace of udev: %m");
r = readlink_malloc("/proc/self/ns/net", &our_ns);
if (r < 0)
return log_error_errno(r, "Failed to read our own network namespace: %m");
if (!streq(our_ns, udev_ns))
return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP),
"Sorry, but --image= is only supported in the main network namespace, since we need access to udev/AF_NETLINK.");
return 0;
}
static int run(int argc, char *argv[]) {
bool secondary = false, remove_directory = false, remove_image = false,
veth_created = false, remove_tmprootdir = false;
@ -4846,6 +4898,10 @@ static int run(int argc, char *argv[]) {
if (r < 0)
goto finish;
r = cant_be_in_netns();
if (r < 0)
goto finish;
r = initialize_rlimits();
if (r < 0)
goto finish;