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Capabilities support #229

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7 changes: 7 additions & 0 deletions configure.ac
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,13 @@ PKG_CHECK_MODULES([LIBPCRE], [libpcre], HAVE_LIBPCRE=yes; AC_DEFINE(HAVE_LIBPCRE
fi
])

PKG_CHECK_MODULES([LIBCAP], [libcap], HAVE_LIBCAP=yes; AC_DEFINE(HAVE_LIBCAP, 1),
[AC_LIB_HAVE_LINKFLAGS(pcre,, [#include <sys/capability.h>], [cap_get_proc();])
if test x$ac_cv_libcap = xyes; then
AC_SUBST([LIBCAP_LIBS], [$LIBCAP])
fi
])

AC_ARG_ENABLE([dns],
[AS_HELP_STRING([--disable-dns], [Disable DNS resolution])],
[dns="$withval"], [dns=yes])
Expand Down
2 changes: 1 addition & 1 deletion src/Makefile.am
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Expand Up @@ -33,4 +33,4 @@ sniproxy_SOURCES = sniproxy.c \
tls.c \
tls.h

sniproxy_LDADD = $(LIBEV_LIBS) $(LIBPCRE_LIBS) $(LIBUDNS_LIBS)
sniproxy_LDADD = $(LIBEV_LIBS) $(LIBPCRE_LIBS) $(LIBUDNS_LIBS) $(LIBCAP_LIBS)
57 changes: 57 additions & 0 deletions src/sniproxy.c
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,10 @@
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/resource.h>
#ifdef HAVE_LIBCAP
#include <sys/prctl.h>
#include <sys/capability.h>
#endif
#include <signal.h>
#include <errno.h>
#include <ev.h>
Expand Down Expand Up @@ -235,6 +239,30 @@ drop_perms(const char *username, const char *groupname) {
gid = group->gr_gid;
}

#ifdef HAVE_LIBCAP
cap_t caps;
cap_value_t cap_list[1];

/* add permitted flag to capability needed for IP_TRANSPARENT */
if (CAP_IS_SUPPORTED(CAP_NET_RAW)) {
caps = cap_get_proc();
if (caps == NULL)
fatal("cap_get_proc(): %s", strerror(errno));

cap_list[0] = CAP_NET_RAW;
if (cap_set_flag(caps, CAP_PERMITTED, 1, cap_list, CAP_SET) == -1)
fatal("cap_set_flags(): %s", strerror(errno));

if (cap_set_proc(caps) == -1)
fatal("cap_set_proc(): %s", strerror(errno));

cap_free(caps);

/* keep capabilities after setuid */
prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0);
}
#endif

/* drop any supplementary groups */
if (setgroups(1, &gid) < 0)
fatal("setgroups(): %s", strerror(errno));
Expand All @@ -245,6 +273,35 @@ drop_perms(const char *username, const char *groupname) {

if (setuid(user->pw_uid) < 0)
fatal("setuid(): %s", strerror(errno));

#ifdef HAVE_LIBCAP
/* enable capability needed for IP_TRANSPARENT */
if (CAP_IS_SUPPORTED(CAP_NET_RAW)) {
caps = cap_get_proc();
if (caps == NULL)
fatal("cap_get_proc(): %s", strerror(errno));

/* remove every capability from the list */
cap_clear(caps);
cap_list[0] = CAP_NET_RAW;
/* take back capability */
if (cap_set_flag(caps, CAP_PERMITTED, 1, cap_list, CAP_SET) == -1)
fatal("cap_set_flags(): %s", strerror(errno));
/* take back capability */
if (cap_set_flag(caps, CAP_EFFECTIVE, 1, cap_list, CAP_SET) == -1)
fatal("cap_set_flags(): %s", strerror(errno));

if (cap_set_proc(caps) == -1)
fatal("back cap_set_proc(): %s", strerror(errno));
/* from now on it the new capability list is active,
* no other capabilities may be enabled */

cap_free(caps);

/* disable keeping capabilities across setuid */
prctl(PR_SET_KEEPCAPS, 0, 0, 0, 0);
}
#endif
}

static void
Expand Down