Dropping root priviledges using Linux Capabilities

diff --git a/tcpdump.c b/tcpdump.c
index 587ed32170ac925df013cd2d8cb8473737e71003..f6b3f34b538b351560a9703b3d79389a88c99f81 100644 (file)
--- a/tcpdump.c
+++ b/tcpdump.c
@@ -74,6 +74,10 @@ extern int SIZE_BUF;
 #include <errno.h>
 #endif /* WIN32 */
 
+/* capabilities convinience library */
+#ifdef HAVE_CAP_NG_H
+#include <cap-ng.h>
+#endif /* HAVE_CAP_NG_H */
 
 #include "netdissect.h"
 #include "interface.h"
@@ -532,6 +536,19 @@ droproot(const char *username, const char *chroot_dir)
                                exit(1);
                        }
                }
+#ifdef HAVE_CAP_NG_H
+               int ret = capng_change_id(pw->pw_uid, pw->pw_gid, CAPNG_NO_FLAG);
+               if (ret < 0) {
+                       printf("error : ret %d\n", ret);
+               }
+               /* We don't need CAP_SETUID and CAP_SETGID */
+               capng_update(CAPNG_DROP, CAPNG_EFFECTIVE, CAP_SETUID);
+               capng_update(CAPNG_DROP, CAPNG_EFFECTIVE, CAP_SETUID);
+               capng_update(CAPNG_DROP, CAPNG_PERMITTED, CAP_SETUID);
+               capng_update(CAPNG_DROP, CAPNG_PERMITTED, CAP_SETUID);
+               capng_apply(CAPNG_SELECT_BOTH);
+
+#else
                if (initgroups(pw->pw_name, pw->pw_gid) != 0 ||
                    setgid(pw->pw_gid) != 0 || setuid(pw->pw_uid) != 0) {
                        fprintf(stderr, "tcpdump: Couldn't change to '%.32s' uid=%lu gid=%lu: %s\n",
@@ -541,6 +558,7 @@ droproot(const char *username, const char *chroot_dir)
                            pcap_strerror(errno));
                        exit(1);
                }
+#endif /* HAVE_CAP_NG_H */
        }
        else {
                fprintf(stderr, "tcpdump: Couldn't find user '%.32s'\n",
@@ -1295,9 +1313,31 @@ main(int argc, char **argv)
         * Switching to the -Z user ID only after opening the first
         * savefile doesn't handle the general case.
         */
+
+#ifdef HAVE_CAP_NG_H
+       /* We are running as root and we will be writing to savefile */
+       if ((getuid() == 0 || geteuid() == 0) && WFileName) {
+               if (username) {
+                       /* Drop all capabilities from effective set */
+                       capng_clear(CAPNG_EFFECTIVE);
+                       /* Add capabilities we will need*/
+                       capng_update(CAPNG_ADD, CAPNG_PERMITTED, CAP_SETUID);
+                       capng_update(CAPNG_ADD, CAPNG_PERMITTED, CAP_SETGID);
+                       capng_update(CAPNG_ADD, CAPNG_PERMITTED, CAP_DAC_OVERRIDE);
+
+                       capng_update(CAPNG_ADD, CAPNG_EFFECTIVE, CAP_SETUID);
+                       capng_update(CAPNG_ADD, CAPNG_EFFECTIVE, CAP_SETGID);
+                       capng_update(CAPNG_ADD, CAPNG_EFFECTIVE, CAP_DAC_OVERRIDE);
+
+                       capng_apply(CAPNG_SELECT_BOTH);
+               }
+       }
+#endif /* HAVE_CAP_NG_H */
+
        if (getuid() == 0 || geteuid() == 0) {
                if (username || chroot_dir)
                        droproot(username, chroot_dir);
+
        }
 #endif /* WIN32 */
 
@@ -1318,6 +1358,10 @@ main(int argc, char **argv)
                  MakeFilename(dumpinfo.CurrentFileName, WFileName, 0, 0);
 
                p = pcap_dump_open(pd, dumpinfo.CurrentFileName);
+#ifdef HAVE_CAP_NG_H
+        /* Give up capabilities, clear Effective set */
+        capng_clear(CAPNG_EFFECTIVE);
+#endif
                if (p == NULL)
                        error("%s", pcap_geterr(pd));
                if (Cflag != 0 || Gflag != 0) {
@@ -1649,7 +1693,15 @@ dump_packet_and_trunc(u_char *user, const struct pcap_pkthdr *h, const u_char *s
                        else
                                MakeFilename(dump_info->CurrentFileName, dump_info->WFileName, 0, 0);
 
+#ifdef HAVE_CAP_NG_H
+                       capng_update(CAPNG_ADD, CAPNG_EFFECTIVE, CAP_DAC_OVERRIDE);
+                       capng_apply(CAPNG_EFFECTIVE);
+#endif /* HAVE_CAP_NG_H */
                        dump_info->p = pcap_dump_open(dump_info->pd, dump_info->CurrentFileName);
+#ifdef HAVE_CAP_NG_H
+                       capng_update(CAPNG_DROP, CAPNG_EFFECTIVE, CAP_DAC_OVERRIDE);
+                       capng_apply(CAPNG_EFFECTIVE);
+#endif /* HAVE_CAP_NG_H */
                        if (dump_info->p == NULL)
                                error("%s", pcap_geterr(pd));
                }