Make a half-hearted attempt to handle multiple presence words in radiotap.

[libpcap] / gencode.c

diff --git a/gencode.c b/gencode.c
index 481c4d9c358a5ade099ba458a907502b837c8139..ad1324b09d6270e8be8ce5c9ca01e11129db7d6b 100644 (file)
--- a/gencode.c
+++ b/gencode.c
@@ -2448,8 +2448,9 @@ gen_load_802_11_header_len(struct slist *s, struct slist *snext)
        struct slist *sjset_data_frame_1;
        struct slist *sjset_data_frame_2;
        struct slist *sjset_qos;
-       struct slist *sjset_radiotap_flags;
-       struct slist *sjset_radiotap_tsft;
+       struct slist *sjset_radiotap_flags_present;
+       struct slist *sjset_radiotap_ext_present;
+       struct slist *sjset_radiotap_tsft_present;
        struct slist *sjset_tsft_datapad, *sjset_notsft_datapad;
        struct slist *s_roundup;
 
@@ -2565,32 +2566,54 @@ gen_load_802_11_header_len(struct slist *s, struct slist *snext)
         * little-endian, so we byte-swap all of the values
         * we test against, as they will be loaded as big-endian
         * values.
+        *
+        * XXX - in the general case, we would have to scan through
+        * *all* the presence bits, if there's more than one word of
+        * presence bits.  That would require a loop, meaning that
+        * we wouldn't be able to run the filter in the kernel.
+        *
+        * We assume here that the Atheros adapters that insert the
+        * annoying padding don't have multiple antennae and therefore
+        * do not generate radiotap headers with multiple presence words.
         */
        if (linktype == DLT_IEEE802_11_RADIO) {
                /*
                 * Is the IEEE80211_RADIOTAP_FLAGS bit (0x0000002) set
-                * in the presence flag?
+                * in the first presence flag word?
                 */
                sjset_qos->s.jf = s2 = new_stmt(BPF_LD|BPF_ABS|BPF_W);
                s2->s.k = 4;
                sappend(s, s2);
 
-               sjset_radiotap_flags = new_stmt(JMP(BPF_JSET));
-               sjset_radiotap_flags->s.k = SWAPLONG(0x00000002);
-               sappend(s, sjset_radiotap_flags);
+               sjset_radiotap_flags_present = new_stmt(JMP(BPF_JSET));
+               sjset_radiotap_flags_present->s.k = SWAPLONG(0x00000002);
+               sappend(s, sjset_radiotap_flags_present);
 
                /*
                 * If not, skip all of this.
                 */
-               sjset_radiotap_flags->s.jf = snext;
+               sjset_radiotap_flags_present->s.jf = snext;
+
+               /*
+                * Otherwise, is the "extension" bit set in that word?
+                */
+               sjset_radiotap_ext_present = new_stmt(JMP(BPF_JSET));
+               sjset_radiotap_ext_present->s.k = SWAPLONG(0x80000000);
+               sappend(s, sjset_radiotap_ext_present);
+               sjset_radiotap_flags_present->s.jt = sjset_radiotap_ext_present;
+
+               /*
+                * If so, skip all of this.
+                */
+               sjset_radiotap_ext_present->s.jt = snext;
 
                /*
                 * Otherwise, is the IEEE80211_RADIOTAP_TSFT bit set?
                 */
-               sjset_radiotap_tsft = sjset_radiotap_flags->s.jt =
-                   new_stmt(JMP(BPF_JSET));
-               sjset_radiotap_tsft->s.k = SWAPLONG(0x00000001);
-               sappend(s, sjset_radiotap_tsft);
+               sjset_radiotap_tsft_present = new_stmt(JMP(BPF_JSET));
+               sjset_radiotap_tsft_present->s.k = SWAPLONG(0x00000001);
+               sappend(s, sjset_radiotap_tsft_present);
+               sjset_radiotap_ext_present->s.jf = sjset_radiotap_tsft_present;
 
                /*
                 * If IEEE80211_RADIOTAP_TSFT is set, the flags field is
@@ -2601,9 +2624,10 @@ gen_load_802_11_header_len(struct slist *s, struct slist *snext)
                 * Test whether the IEEE80211_RADIOTAP_F_DATAPAD bit (0x20)
                 * is set.
                 */
-               sjset_radiotap_tsft->s.jt = s2 = new_stmt(BPF_LD|BPF_ABS|BPF_B);
+               s2 = new_stmt(BPF_LD|BPF_ABS|BPF_B);
                s2->s.k = 16;
                sappend(s, s2);
+               sjset_radiotap_tsft_present->s.jt = s2;
 
                sjset_tsft_datapad = new_stmt(JMP(BPF_JSET));
                sjset_tsft_datapad->s.k = 0x20;
@@ -2617,9 +2641,10 @@ gen_load_802_11_header_len(struct slist *s, struct slist *snext)
                 * Test whether the IEEE80211_RADIOTAP_F_DATAPAD bit (0x20)
                 * is set.
                 */
-               sjset_radiotap_tsft->s.jf = s2 = new_stmt(BPF_LD|BPF_ABS|BPF_B);
+               s2 = new_stmt(BPF_LD|BPF_ABS|BPF_B);
                s2->s.k = 8;
                sappend(s, s2);
+               sjset_radiotap_tsft_present->s.jf = s2;
 
                sjset_notsft_datapad = new_stmt(JMP(BPF_JSET));
                sjset_notsft_datapad->s.k = 0x20;