On Mon, Sep 27, 2021 at 04:18:34PM -0500, Eric Blake wrote: > On Fri, Jul 23, 2021 at 11:33:03AM +0100, Richard W.M. Jones wrote: > > Under SELinux, Unix domain sockets have two labels. One is on the > > disk and can be set with commands such as chcon(1). There is a > > different label stored in memory (called the process label). This can > > only be set by the process creating the socket. When using SELinux + > > SVirt and wanting qemu to be able to connect to a qemu-nbd instance, > > you must set both labels correctly first. > > > > For qemu-nbd the options to set the second label are awkward. You can > > create the socket in a wrapper program and then exec into qemu-nbd. > > Or you could try something with LD_PRELOAD. > > > > This commit adds the ability to set the label straightforwardly on the > > command line, via the new --selinux-label flag. (The name of the flag > > is the same as the equivalent nbdkit option.) > > > > A worked example showing how to use the new option can be found in > > this bug: https://bugzilla.redhat.com/show_bug.cgi?id=1984938 > > > > Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1984938 > > Signed-off-by: Richard W.M. Jones <rjo...@redhat.com> > > --- > > I'm making one tweak to your patch before sending the pull request: > > > +++ b/qemu-nbd.c > > @@ -64,6 +68,7 @@ > > #define QEMU_NBD_OPT_FORK 263 > > #define QEMU_NBD_OPT_TLSAUTHZ 264 > > #define QEMU_NBD_OPT_PID_FILE 265 > > +#define QEMU_NBD_OPT_SELINUX_LABEL 266 > > > > #define MBR_SIZE 512 > > > > @@ -116,6 +121,9 @@ static void usage(const char *name) > > " --fork fork off the server process and exit the > > parent\n" > > " once the server is running\n" > > " --pid-file=PATH store the server's process ID in the given > > file\n" > > +#ifdef CONFIG_SELINUX > > +" --selinux-label=LABEL set SELinux process label on listening > > socket\n" > > +#endif > > The new option is only conditionally advertised under --help (qemu-nbd > lacks a stable machine-parseable output, so scraping --help output > will have to do for now)... > > > #if HAVE_NBD_DEVICE > > "\n" > > "Kernel NBD client support:\n" > > @@ -532,6 +540,8 @@ int main(int argc, char **argv) > > { "trace", required_argument, NULL, 'T' }, > > { "fork", no_argument, NULL, QEMU_NBD_OPT_FORK }, > > { "pid-file", required_argument, NULL, QEMU_NBD_OPT_PID_FILE }, > > + { "selinux-label", required_argument, NULL, > > + QEMU_NBD_OPT_SELINUX_LABEL }, > > ...but is unconditionally supported as a long option even when support > was not compiled in... > > > { NULL, 0, NULL, 0 } > > }; > > int ch; > > @@ -558,6 +568,7 @@ int main(int argc, char **argv) > > int old_stderr = -1; > > unsigned socket_activation; > > const char *pid_file_name = NULL; > > + const char *selinux_label = NULL; > > BlockExportOptions *export_opts; > > > > #ifdef CONFIG_POSIX > > @@ -747,6 +758,9 @@ int main(int argc, char **argv) > > case QEMU_NBD_OPT_PID_FILE: > > pid_file_name = optarg; > > break; > > + case QEMU_NBD_OPT_SELINUX_LABEL: > > + selinux_label = optarg; > > + break; > > } > > } > > > > @@ -938,6 +952,16 @@ int main(int argc, char **argv) > > } else { > > backlog = MIN(shared, SOMAXCONN); > > } > > + if (sockpath && selinux_label) { > > +#ifdef CONFIG_SELINUX > > + if (setsockcreatecon_raw(selinux_label) == -1) { > > + error_report("Cannot set SELinux socket create context " > > + "to %s: %s", > > + selinux_label, strerror(errno)); > > + exit(EXIT_FAILURE); > > + } > > +#endif > > ...but here we silently ignore it if support is not compiled in. > Better is to issue an error message about using an unsupported option, > so I'll squash this in: > > diff --git i/qemu-nbd.c w/qemu-nbd.c > index 5dc82c419255..94f8ec07c064 100644 > --- i/qemu-nbd.c > +++ w/qemu-nbd.c > @@ -962,6 +962,9 @@ int main(int argc, char **argv) > selinux_label, strerror(errno)); > exit(EXIT_FAILURE); > } > +#else > + error_report("SELinux support not enabled in this binary"); > + exit(EXIT_FAILURE); > #endif > } > saddr = nbd_build_socket_address(sockpath, bindto, port); > @@ -978,6 +981,9 @@ int main(int argc, char **argv) > strerror(errno)); > exit(EXIT_FAILURE); > } > +#else > + error_report("SELinux support not enabled in this binary"); > + exit(EXIT_FAILURE); > #endif > } > } else { >
Good idea, thanks. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/