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shmounts: terminate the forked off mount namespace capture helper (latest-candidate) #386

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merged 1 commit into from
Mar 18, 2024
+15 −8
Merged

shmounts: terminate the forked off mount namespace capture helper (latest-candidate) #386

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23 changes: 15 additions & 8 deletions shmounts/setup-shmounts.c
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Original file line number Diff line number Diff line change
Expand Up @@ -66,6 +66,12 @@ int mkdir_p(const char *dir, mode_t mode)
return 0;
}

__attribute__((noreturn))
static void die(const char *s) {
perror(s);
exit(1);
}

int setup_ns() {
int wstatus;
ssize_t ret;
Expand Down Expand Up @@ -94,40 +100,41 @@ int setup_ns() {
ret = lxc_read_nointr(pipe_fds[0], nspath, 1);
close(pipe_fds[0]);
if (ret < 0) {
return -1;
die("cannot read from pipe");
}

// Create the mountpoint
if (mkdir("/var/snap/lxd/common/ns", 0700) < 0 && errno != EEXIST) {
return -1;
die("cannot mkdir /var/snap/lxd/common/ns");
}

// Mount a tmpfs
if (mount("tmpfs", "/var/snap/lxd/common/ns", "tmpfs", 0, "size=1M,mode=0700") < 0) {
return -1;
die("cannot mount tmpfs on /var/snap/lxd/common/ns");
}

// Mark the tmpfs mount as MS_PRIVATE
if (mount("none", "/var/snap/lxd/common/ns", NULL, MS_REC|MS_PRIVATE, NULL) < 0) {
return -1;
die("cannot change propagation on /var/snap/lxd/common/ns");
}

// Store reference to the mntns
if (snprintf(nspath, PATH_MAX, "/proc/%u/ns/mnt", (unsigned)getppid()) < 0) {
return -1;
die("cannot capture reference to parent's mount ns");
}

fd = open("/var/snap/lxd/common/ns/shmounts", O_CREAT | O_RDWR, 0600);
if (fd < 0) {
return -1;
die("cannot open /var/snap/lxd/common/ns/shmounts");
}
close(fd);

if (mount(nspath, "/var/snap/lxd/common/ns/shmounts", NULL, MS_BIND, NULL) < 0) {
return -1;
die("cannot bind mount ns to /var/snap/lxd/common/ns/shmounts");
}

return 0;
/* the child is done */
exit(0);
}

close(pipe_fds[0]);
Expand Down