[syslog-ng] [PATCH RFC] Use cap_syslog when it is available (v3)

[Balazs Scheidler]

Hi,

Can you please send the original patch? v3 never made it to the list,
and the patch in this email is quoted.

Thanks.

On Mon, 2011-04-18 at 20:26 +0200, Gergely Nagy wrote:
> (forwarding the original mail, as it looks like it never made to the
> list)
> 
> Serge Hallyn <serge.hallyn at canonical.com> writes:
> 
> > (A-ha - great idea from Andrew - we *can* figure out whether the
> > kernel knows about CAP_SYSLOG, using the bounding set API)
> >
> > If cap_syslog exists, the kernel will complain (once) that we only
> > have cap_sys_admin.  Additionally, using cap_syslog instead of
> > cap_sys_admin significantly lowers the unneeded privs we are
> > using.
> >
> > Changelog:
> > 	v2: At startup, detect whether libcap knows about CAP_SYSLOG.
> > 	    (Thanks to Gergely Nagy for pointing out that case)
> > 	v3: Andrew Morgan pointed out a nice way to detect whether
> > 	    the kernel has CAP_SYSLOG.  Thanks, Andrew!
> >
> > Signed-off-by: Serge Hallyn <serge.hallyn at ubuntu.com>
> > ---
> >  lib/gprocess.c          |   48 ++++++++++++++++++++++++++++++++++++++++++++++-
> >  lib/gprocess.h          |    2 +-
> >  modules/affile/affile.c |    4 +++
> >  syslog-ng/main.c        |   10 ++------
> >  4 files changed, 55 insertions(+), 9 deletions(-)
> >
> > diff --git a/lib/gprocess.c b/lib/gprocess.c
> > index d9a2dfb..f9bda7b 100644
> > --- a/lib/gprocess.c
> > +++ b/lib/gprocess.c
> > @@ -98,6 +98,7 @@ static gint startup_result_pipe[2] = { -1, -1 };
> >  static gint init_result_pipe[2] = { -1, -1 };
> >  static GProcessKind process_kind = G_PK_STARTUP;
> >  static gboolean stderr_present = TRUE;
> > +static int have_capsyslog = FALSE;
> >  
> >  /* global variables */
> >  static struct
> > @@ -210,6 +211,14 @@ g_process_cap_modify(int capability, int onoff)
> >    if (!process_opts.caps)
> >      return TRUE;
> >  
> > +#ifdef CAP_SYSLOG
> > +  /*
> > +   * if libcap or kernel doesn't support cap_syslog, then resort to
> > +   * cap_sys_admin
> > +   */
> > +  if (capability == CAP_SYSLOG && !have_capsyslog)
> > +    capability = CAP_SYS_ADMIN;
> > +#endif
> >    caps = cap_get_proc();
> >    if (!caps)
> >      return FALSE;
> > @@ -416,7 +425,7 @@ g_process_set_working_dir(const gchar *cwd)
> >   * capability set. The process will change its capabilities to this value
> >   * during startup, provided it has enough permissions to do so.
> >   **/
> > -void 
> > +static void 
> >  g_process_set_caps(const gchar *caps)
> >  {
> >    if (!process_opts.caps)
> > @@ -879,6 +888,43 @@ g_process_change_dir(void)
> >  }
> >  
> >  /**
> > + * g_process_setup_caps(void)
> > + *
> > + * NOTE: polling /proc/kmsg requires cap_sys_admin, otherwise it'll always
> > + * indicate readability. Enabling/disabling cap_sys_admin on every poll
> > + * invocation seems to be too expensive. So I enable it for now.
> > + */
> > +void
> > +g_process_setup_caps(void)
> > +{
> > +  int ret;
> > +  gchar * capsstr = "cap_net_bind_service,cap_net_broadcast,cap_net_raw,"
> > +                   "cap_dac_read_search,cap_dac_override,cap_chown,cap_fowner=p "
> > +                   "cap_sys_admin=ep";
> > +#ifdef CAP_SYSLOG
> > +  cap_t caps;
> > +
> > +  /* Check whether cap_syslog exists.  If not, get cap_sys_admin, else get
> > +   * cap_syslog */
> > +  caps = cap_from_text("cap_syslog=p");
> > +  if (caps) {
> > +    cap_free(caps);
> > +    /* libcap knows it, does the kernel? */
> > +    ret = prctl(PR_CAPBSET_READ, CAP_SYSLOG);
> > +    if (ret != -1) {
> > +	    /* kernel knows cap_syslog!  Use it */
> > +	    capsstr = "cap_net_bind_service,cap_net_broadcast,cap_net_raw,"
> > +		      "cap_dac_read_search,cap_dac_override,cap_chown,cap_fowner=p "
> > +		      "cap_syslog=ep";
> > +	    have_capsyslog = TRUE;
> > +    }
> > +  }
> > +#endif
> > +
> > +  g_process_set_caps(capsstr);
> > +}
> > +
> > +/**
> >   * g_process_send_result:
> >   * @ret_num: exit code of the process
> >   *
> > diff --git a/lib/gprocess.h b/lib/gprocess.h
> > index cda35b0..4ad0866 100644
> > --- a/lib/gprocess.h
> > +++ b/lib/gprocess.h
> > @@ -66,7 +66,7 @@ void g_process_set_chroot(const gchar *chroot);
> >  void g_process_set_pidfile(const gchar *pidfile);
> >  void g_process_set_pidfile_dir(const gchar *pidfile_dir);
> >  void g_process_set_working_dir(const gchar *cwd);
> > -void g_process_set_caps(const gchar *caps);
> > +void g_process_setup_caps(void);
> >  void g_process_set_argv_space(gint argc, gchar **argv);
> >  void g_process_set_use_fdlimit(gboolean use);
> >  void g_process_set_check(gint check_period, gboolean (*check_fn)(void));
> > diff --git a/modules/affile/affile.c b/modules/affile/affile.c
> > index a713bfc..358a083 100644
> > --- a/modules/affile/affile.c
> > +++ b/modules/affile/affile.c
> > @@ -59,7 +59,11 @@ affile_open_file(gchar *name, gint flags,
> >    if (privileged)
> >      {
> >        g_process_cap_modify(CAP_DAC_READ_SEARCH, TRUE);
> > +#ifdef CAP_SYSLOG
> > +      g_process_cap_modify(CAP_SYSLOG, TRUE);
> > +#else
> >        g_process_cap_modify(CAP_SYS_ADMIN, TRUE);
> > +#endif
> >      }
> >    else
> >      {
> > diff --git a/syslog-ng/main.c b/syslog-ng/main.c
> > index 7e81f2f..5e62c1f 100644
> > --- a/syslog-ng/main.c
> > +++ b/syslog-ng/main.c
> > @@ -167,13 +167,9 @@ main(int argc, char *argv[])
> >  
> >    g_process_set_argv_space(argc, (gchar **) argv);
> >    
> > -  /* NOTE: polling /proc/kmsg requires cap_sys_admin, otherwise it'll always
> > -   * indicate readability. Enabling/disabling cap_sys_admin on every poll
> > -   * invocation seems to be too expensive. So I enable it for now. */
> > -  
> > -  g_process_set_caps("cap_net_bind_service,cap_net_broadcast,cap_net_raw,"
> > -                     "cap_dac_read_search,cap_dac_override,cap_chown,cap_fowner=p "
> > -                     "cap_sys_admin=ep");
> > +  /* Set up the minimal privilege we'll need */
> > +  g_process_setup_caps();
> > +
> >    ctx = g_option_context_new("syslog-ng");
> >    g_process_add_option_group(ctx);
> >    msg_add_option_group(ctx);
> 

-- 
Bazsi