linux: reserve space for DLT_LINUX_SLL2 on all cooked captures.

Don't just do it if we're using DLT_LINUX_SLL2 up front; that can be
changed by the software using libpcap at any point.

(cherry picked from commit 17a48ca162de1a6d40a3b767eb318c2899666eb4)

diff --git a/pcap-linux.c b/pcap-linux.c
index 6b09c798787ebeb3028d7c7b6bd61e393ed3a220..8dbf89bca393ca596b98dee24e837fd9c22cea43 100644 (file)
--- a/pcap-linux.c
+++ b/pcap-linux.c
@@ -2891,22 +2891,22 @@ create_ring(pcap_t *handle, int *status)
        tp_reserve = VLAN_TAG_LEN;
 
        /*
-        * If we're using DLT_LINUX_SLL2, reserve space for a
-        * DLT_LINUX_SLL2 header.
+        * If we're capturing in cooked mode, reserve space for
+        * a DLT_LINUX_SLL2 header; we don't know yet whether
+        * we'll be using DLT_LINUX_SLL or DLT_LINUX_SLL2, as
+        * that can be changed on an open device, so we reserve
+        * space for the larger of the two.
         *
         * XXX - we assume that the kernel is still adding
-        * 16 bytes of extra space; that happens to
-        * correspond to SLL_HDR_LEN (whether intentionally
-        * or not - the kernel code has a raw "16" in
-        * the expression), so we subtract SLL_HDR_LEN
-        * from SLL2_HDR_LEN to get the additional space
-        * needed.  That also means we don't bother reserving
-        * any additional space if we're using DLT_LINUX_SLL.
+        * 16 bytes of extra space, so we subtract 16 from
+        * SLL2_HDR_LEN to get the additional space needed.
+        * (Are they doing that for DLT_LINUX_SLL, the link-
+        * layer header for which is 16 bytes?)
         *
-        * XXX - should we use TPACKET_ALIGN(SLL2_HDR_LEN - SLL_HDR_LEN)?
+        * XXX - should we use TPACKET_ALIGN(SLL2_HDR_LEN - 16)?
         */
-       if (handle->linktype == DLT_LINUX_SLL2)
-               tp_reserve += SLL2_HDR_LEN - SLL_HDR_LEN;
+       if (handlep->cooked)
+               tp_reserve += SLL2_HDR_LEN - 16;
 
        /*
         * Try to request that amount of reserve space.