Make prepare_tpacket_socket() a bit more of a straightforward gauntlet.

Try TPACKET_V3 first, if it's defined and if immediate mode was not
requested; return if that succeeds or if it fails for a reason other
than "the kernel doesn't support TPACKET_V3".  Then try TPACKET_V2, if
it's defined; return if that succeeds or fails for a reson other than
"the kernel doesn't support TPACKET_V2".  Then go with TPACKET_V1 or
TPACKET_V1_64.

Don't set handlep->tp_version to TPACKET_V1 and handlep->tp_hdrlen to
sizeof(struct tpacket_hdr) until after we've found out that the kernel
supports neither TPACKET_V2 nor TPACKET_V3; init_tpacket() sets them if
it succeeds.

diff --git a/pcap-linux.c b/pcap-linux.c
index 92247228e049b401e4e106cd34fb6ddcff2014c9..bf54340bc4feeabae22285b7036adf931e0c78ae 100644 (file)
--- a/pcap-linux.c
+++ b/pcap-linux.c
@@ -3573,7 +3573,10 @@ init_tpacket(pcap_t *handle, int version, const char *version_str)
        int val = version;
        socklen_t len = sizeof(val);
 
-       /* Probe whether kernel supports the specified TPACKET version */
+       /*
+        * Probe whether kernel supports the specified TPACKET version;
+        * this also gets the length of the header for that version.
+        */
        if (getsockopt(handle->fd, SOL_PACKET, PACKET_HDRLEN, &val, &len) < 0) {
                if (errno == ENOPROTOOPT || errno == EINVAL)
                        return 1;       /* no */
@@ -3629,11 +3632,10 @@ prepare_tpacket_socket(pcap_t *handle)
        int ret;
 #endif
 
-       handlep->tp_version = TPACKET_V1;
-       handlep->tp_hdrlen = sizeof(struct tpacket_hdr);
-
 #ifdef HAVE_TPACKET3
        /*
+        * Try setting the version to TPACKET_V3.
+        *
         * The only mode in which buffering is done on PF_PACKET
         * sockets, so that packets might not be delivered
         * immediately, is TPACKET_V3 mode.
@@ -3642,37 +3644,59 @@ prepare_tpacket_socket(pcap_t *handle)
         * if the user has requested immediate mode, we don't
         * use TPACKET_V3.
         */
-       if (handle->opt.immediate)
-               ret = 1; /* pretend TPACKET_V3 couldn't be set */
-       else
+       if (!handle->opt.immediate) {
                ret = init_tpacket(handle, TPACKET_V3, "TPACKET_V3");
-       if (-1 == ret) {
-               /* Error during setting up TPACKET_V3. */
-               return -1;
-       } else if (1 == ret) {
-               /* TPACKET_V3 not supported - fall back to TPACKET_V2. */
+               if (ret == 0) {
+                       /*
+                        * Success.
+                        */
+                       return 1;
+               }
+               if (ret == -1) {
+                       /*
+                        * We failed for some reason other than "the
+                        * kernel doesn't support TPACKET_V3".
+                        */
+                       return -1;
+               }
+       }
 #endif /* HAVE_TPACKET3 */
 
 #ifdef HAVE_TPACKET2
-               ret = init_tpacket(handle, TPACKET_V2, "TPACKET_V2");
-               if (-1 == ret) {
-                       /* Error during setting up TPACKET_V2. */
-                       return -1;
-               }
+       /*
+        * Try setting the version to TPACKET_V2.
+        */
+       ret = init_tpacket(handle, TPACKET_V2, "TPACKET_V2");
+       if (ret == 0) {
+               /*
+                * Success.
+                */
+               return 1;
+       }
+       if (ret == -1) {
+               /*
+                * We failed for some reason other than "the
+                * kernel doesn't support TPACKET_V2".
+                */
+               return -1;
+       }
 #endif /* HAVE_TPACKET2 */
 
-#ifdef HAVE_TPACKET3
-       }
-#endif /* HAVE_TPACKET3 */
+       /*
+        * OK, we're using TPACKET_V1, as that's all the kernel supports.
+        */
+       handlep->tp_version = TPACKET_V1;
+       handlep->tp_hdrlen = sizeof(struct tpacket_hdr);
 
        /*
-        * 32-bit userspace + 64-bit kernel + tpacket_v1 are not compatible with
+        * 32-bit userspace + 64-bit kernel + TPACKET_V1 are not compatible with
         * each other due to platform-dependent data type size differences.
         *
-        * TPACKET_V1_64 allows using a 64-bit tpacket_v1 header from 32-bit
-        * userspace.
+        * If we have a 32-bit userland and a 64-bit kernel, use an
+        * internally-defined TPACKET_V1_64, with which we use a 64-bit
+        * version of the data structures.
         */
-       if (handlep->tp_version == TPACKET_V1 && sizeof(long) == 4) {
+       if (sizeof(long) == 4) {
                 struct utsname utsname;
                 uname(&utsname);
                 if (!strcmp("x86_64", utsname.machine)) {