Switch user ID/root directory with -Z before opening savefiles for output.

In addition to Paul's change, I added a comment explaining why we do
this, and explaining that doing so after opening the first savefile
doesn't help with subsequent savefiles, so you'll have to come up with a
better fix if you want the savefiles opened by the original UID or
outside the chroot.

Reviewed-By: Guy Harris <[email protected]>

diff --git a/CREDITS b/CREDITS
index 7f9df5982231985a3f438b9ff61f241d64a1f4ae..5831a3a7bdfa7bda9acad1ca3e92cffaed13c2cc 100644 (file)
--- a/CREDITS
+++ b/CREDITS
@@ -138,6 +138,7 @@ Additional people who have contributed patches:
        Paolo Abeni                     <paolo dot abeni at email dot it>
        Pascal Hennequin                <pascal dot hennequin at int-evry dot fr>
        Pasvorn Boonmark                <boonmark at juniper dot net>
+       Paul Ferrell                    <pflarr at sourceforge dot net>
        Paul Mundt                      <lethal at linux-sh dot org>
        Paul S. Traina                  <pst at freebsd dot org>
        Pavlin Radoslavov               <pavlin at icir dot org>

diff --git a/tcpdump.c b/tcpdump.c
index 7eb3d592ea8b6f37da177359cd4232af5916d00b..a347bc2cc87ffaacdbf5847f3f92714f1c938956 100644 (file)
--- a/tcpdump.c
+++ b/tcpdump.c
@@ -1252,6 +1252,30 @@ main(int argc, char **argv)
                (void)setsignal(SIGHUP, oldhandler);
 #endif /* WIN32 */
 
+#ifndef WIN32
+       /*
+        * If a user name was specified with "-Z", attempt to switch to
+        * that user's UID.  This would probably be used with sudo,
+        * to allow tcpdump to be run in a special restricted
+        * account (if you just want to allow users to open capture
+        * devices, and can't just give users that permission,
+        * you'd make tcpdump set-UID or set-GID).
+        *
+        * Tcpdump doesn't necessarily write only to one savefile;
+        * the general only way to allow a -Z instance to write to
+        * savefiles as the user under whose UID it's run, rather
+        * than as the user specified with -Z, would thus be to switch
+        * to the original user ID before opening a capture file and
+        * then switch back to the -Z user ID after opening the savefile.
+        * Switching to the -Z user ID only after opening the first
+        * savefile doesn't handle the general case.
+        */
+       if (getuid() == 0 || geteuid() == 0) {
+               if (username || chroot_dir)
+                       droproot(username, chroot_dir);
+       }
+#endif /* WIN32 */
+
        if (pcap_setfilter(pd, &fcode) < 0)
                error("%s", pcap_geterr(pd));
        if (WFileName) {
@@ -1305,16 +1329,7 @@ main(int argc, char **argv)
                callback = print_packet;
                pcap_userdata = (u_char *)&printinfo;
        }
-#ifndef WIN32
-       /*
-        * We cannot do this earlier, because we want to be able to open
-        * the file (if done) for writing before giving up permissions.
-        */
-       if (getuid() == 0 || geteuid() == 0) {
-               if (username || chroot_dir)
-                       droproot(username, chroot_dir);
-       }
-#endif /* WIN32 */
+
 #ifdef SIGINFO
        /*
         * We can't get statistics when reading from a file rather