pcap/pcapng: byte-swap the CAN ID field in CAN pseudo-headers for SLL2.

As for LINUX_SLL, so for LINUX_SLL2.

1 files changed, 52 insertions, 1 deletions

diff --git a/wiretap/pcap-common.c b/wiretap/pcap-common.c
index 53811ce75a..5e23fe5dc0 100644
--- a/wiretap/pcap-common.c
+++ b/wiretap/pcap-common.c
@@ -1918,11 +1918,14 @@ struct can_socketcan_hdr {
 };
 
 /*
- * The fake link-layer header of Linux cooked packets.
+ * CAN fake link-layer headers in Linux cooked packets.
  */
 #define LINUX_SLL_PROTOCOL_OFFSET	14	/* protocol */
 #define LINUX_SLL_LEN			16	/* length of the header */
 
+#define LINUX_SLL2_PROTOCOL_OFFSET	0	/* protocol */
+#define LINUX_SLL2_LEN			20	/* length of the header */
+
 /*
  * The protocols we have to check for.
  */
@@ -1973,6 +1976,49 @@ pcap_byteswap_linux_sll_pseudoheader(wtap_rec *rec, guint8 *pd)
 }
 
 static void
+pcap_byteswap_linux_sll2_pseudoheader(wtap_rec *rec, guint8 *pd)
+{
+	guint packet_size;
+	guint16 protocol;
+	struct can_socketcan_hdr *can_socketcan_phdr;
+
+	/*
+	 * Minimum of captured and actual length (just in case the
+	 * actual length < the captured length, which Should Never
+	 * Happen).
+	 */
+	packet_size = rec->rec_header.packet_header.caplen;
+	if (packet_size > rec->rec_header.packet_header.len)
+		packet_size = rec->rec_header.packet_header.len;
+
+	if (packet_size < LINUX_SLL2_LEN) {
+		/* Not enough data to have the protocol */
+		return;
+	}
+
+	protocol = pntoh16(&pd[LINUX_SLL2_PROTOCOL_OFFSET]);
+	if (protocol != LINUX_SLL_P_CAN && protocol != LINUX_SLL_P_CANFD) {
+		/* Not a CAN packet; nothing to fix */
+		return;
+	}
+
+	/*
+	 * Greasy hack, but we never directly dereference any of
+	 * the fields in *can_socketcan_phdr, we just get offsets
+	 * of and addresses of its members and byte-swap it with a
+	 * byte-at-a-time macro, so it's alignment-safe.
+	 */
+	can_socketcan_phdr = (struct can_socketcan_hdr *)(void *)(pd + LINUX_SLL2_LEN);
+
+	if (packet_size < LINUX_SLL2_LEN + sizeof(can_socketcan_phdr->can_id)) {
+		/* Not enough data to have the full CAN ID */
+		return;
+	}
+
+	PBSWAP32((guint8 *)&can_socketcan_phdr->can_id);
+}
+
+static void
 pcap_byteswap_linux_usb_pseudoheader(wtap_rec *rec, guint8 *pd,
     gboolean header_len_64_bytes)
 {
@@ -2373,6 +2419,11 @@ pcap_read_post_process(gboolean is_nokia, int wtap_encap,
 			pcap_byteswap_linux_sll_pseudoheader(rec, pd);
 		break;
 
+	case WTAP_ENCAP_SLL2:
+		if (bytes_swapped)
+			pcap_byteswap_linux_sll2_pseudoheader(rec, pd);
+		break;
+
 	case WTAP_ENCAP_USB_LINUX:
 		if (bytes_swapped)
 			pcap_byteswap_linux_usb_pseudoheader(rec, pd, FALSE);