Don't try PACKET_RESERVE if we can't use TPACKET_V2 or later.

If we're using TPACKET_V1, it's because we have a kernel that doesn't
support TPACKET_V2; such a kernel also doesn't support PACKET_RESERVE,
as TPACKET_V2 and PACKET_RESERVE were both added in 2.6.27.

If we *aren't* using TPACKET_V1, treat any failure of PACKET_RESERVE as
an error, as it should be supported, and we should never get ENOPROTOOPT.

1 files changed, 44 insertions, 38 deletions

diff --git a/pcap-linux.c b/pcap-linux.c
index 0b787496..f0862d7f 100644
--- a/pcap-linux.c
+++ b/pcap-linux.c
@@ -4359,49 +4359,54 @@ create_ring(pcap_t *handle, int *status)
 	 */
 	*status = 0;
 
-#ifdef PACKET_RESERVE
+#ifdef TPACKET_RESERVE
 	/*
-	 * Reserve space for VLAN tag reconstruction.
+	 * TPACKET_V2 and PACKET_RESERVE were both introduced in
+	 * 2.6.27.  If tp_version is for TPACKET_V1, that means
+	 * the kernel doesn't support TPACKET_V2, so it won't
+	 * support PACKET_RESERVE, either.
 	 */
-	tp_reserve = VLAN_TAG_LEN;
+	if (handle->tp_version != TPACKET_V1 &&
+	    handle->tp_version != TPACKET_V1_64) {
+		/*
+		 * Reserve space for VLAN tag reconstruction.
+		 */
+		tp_reserve = VLAN_TAG_LEN;
 
-	/*
-	 * If we're using DLT_LINUX_SLL2, reserve space for a
-	 * DLT_LINUX_SLL2 header.
-	 *
-	 * 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.
-	 *
-	 * XXX - should we reserve space for a DLT_LINUX_SLL header
-	 * if we're using DLT_LINUX_SLL?
-	 *
-	 * XXX - should we use TPACKET_ALIGN(SLL2_HDR_LEN - SLL_HDR_LEN)?
-	 */
-	if (handle->linktype == DLT_LINUX_SLL2)
-		tp_reserve += SLL2_HDR_LEN - SLL_HDR_LEN;
+		/*
+		 * If we're using DLT_LINUX_SLL2, reserve space for a
+		 * DLT_LINUX_SLL2 header.
+		 *
+		 * 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.
+		 *
+		 * XXX - should we use TPACKET_ALIGN(SLL2_HDR_LEN - SLL_HDR_LEN)?
+		 */
+		if (handle->linktype == DLT_LINUX_SLL2)
+			tp_reserve += SLL2_HDR_LEN - SLL_HDR_LEN;
 
-	/*
-	 * Try to request that amount of reserve space.
-	 * This must be done before creating the ring buffer.
-	 * If PACKET_RESERVE is supported, creating the ring
-	 * buffer should be, although if creating the ring
-	 * buffer fails, the PACKET_RESERVE call has no effect,
-	 * so falling back on read-from-the-socket capturing
-	 * won't be affected.
-	 */
-	len = sizeof(tp_reserve);
-	if (setsockopt(handle->fd, SOL_PACKET, PACKET_RESERVE,
-	    &tp_reserve, len) < 0) {
-		if (errno != ENOPROTOOPT) {
+		/*
+		 * Try to request that amount of reserve space.
+		 * This must be done before creating the ring buffer.
+		 * If PACKET_RESERVE is supported, creating the ring
+		 * buffer should be, although if creating the ring
+		 * buffer fails, the PACKET_RESERVE call has no effect,
+		 * so falling back on read-from-the-socket capturing
+		 * won't be affected.
+		 */
+		len = sizeof(tp_reserve);
+		if (setsockopt(handle->fd, SOL_PACKET, PACKET_RESERVE,
+		    &tp_reserve, len) < 0) {
 			/*
-			 * ENOPROTOOPT means "kernel doesn't support
-			 * PACKET_RESERVE", in which case we fall back
-			 * as best we can.
+			 * We treat ENOPROTOOPT as an error, as we
+			 * already determined that we support
+			 * TPACKET_V2 and later; see above.
 			 */
 			pcap_fmt_errmsg_for_errno(handle->errbuf,
 			    PCAP_ERRBUF_SIZE, errno,
@@ -4409,6 +4414,7 @@ create_ring(pcap_t *handle, int *status)
 			*status = PCAP_ERROR;
 			return -1;
 		}
+	} else {
 		/*
 		 * Older kernel, so we can't use PACKET_RESERVE;
 		 * this means we can't reserver extra space