Read the magic number into a byte array.

Apparently, in some C implementations, attempting to do an fread() into
a variable of a 32-bit unsigned integral type with a size of 1 and a
count of 4 returns 0 with an EOF indication; see GitHub pull request

We can make the size be the size of the variable and the count be 1, but
that means that the count returned by an fread() terminated by an EOF
will be 0, not the number of bytes successfully read, so the "truncated
dump file" message will give an invalid count:

	tcpdump: truncated dump file; tried to read 4 file header bytes,
	    only got 0

If, instead, we read into an array of 4 bytes, with a size of 1 and a
count of 4, we'll get the right short count back.

Pass the byte array to the file-type-specific "is this a file of this
type?" routines, so that if we add support for files where the magic
number isn't byte-order dependent (e.g., Microsoft Network Monitor), we
can handle them more cleanly (check for the standard magic number as a
4-byte array, rather than as its numerical value in both the host's byte
order and the byte-swapped byte order).

1 files changed, 14 insertions, 10 deletions

diff --git a/sf-pcap.c b/sf-pcap.c
index 87fc5ce1..f56fff74 100644
--- a/sf-pcap.c
+++ b/sf-pcap.c
@@ -150,9 +150,10 @@ struct pcap_sf {
  * relevant information from the header.
  */
 pcap_t *
-pcap_check_header(bpf_u_int32 magic, FILE *fp, u_int precision, char *errbuf,
+pcap_check_header(const uint8_t *magic, FILE *fp, u_int precision, char *errbuf,
 		  int *err)
 {
+	bpf_u_int32 magic_int;
 	struct pcap_file_header hdr;
 	size_t amt_read;
 	pcap_t *p;
@@ -169,11 +170,14 @@ pcap_check_header(bpf_u_int32 magic, FILE *fp, u_int precision, char *errbuf,
 	 * number for a pcap savefile, or for a byte-swapped pcap
 	 * savefile.
 	 */
-	if (magic != TCPDUMP_MAGIC && magic != KUZNETZOV_TCPDUMP_MAGIC &&
-	    magic != NSEC_TCPDUMP_MAGIC) {
-		magic = SWAPLONG(magic);
-		if (magic != TCPDUMP_MAGIC && magic != KUZNETZOV_TCPDUMP_MAGIC &&
-		    magic != NSEC_TCPDUMP_MAGIC)
+	memcpy(&magic_int, magic, sizeof(magic_int));
+	if (magic_int != TCPDUMP_MAGIC &&
+	    magic_int != KUZNETZOV_TCPDUMP_MAGIC &&
+	    magic_int != NSEC_TCPDUMP_MAGIC) {
+		magic_int = SWAPLONG(magic_int);
+		if (magic_int != TCPDUMP_MAGIC &&
+		    magic_int != KUZNETZOV_TCPDUMP_MAGIC &&
+		    magic_int != NSEC_TCPDUMP_MAGIC)
 			return (NULL);	/* nope */
 		swapped = 1;
 	}
@@ -182,7 +186,7 @@ pcap_check_header(bpf_u_int32 magic, FILE *fp, u_int precision, char *errbuf,
 	 * They are.  Put the magic number in the header, and read
 	 * the rest of the header.
 	 */
-	hdr.magic = magic;
+	hdr.magic = magic_int;
 	amt_read = fread(((char *)&hdr) + sizeof hdr.magic, 1,
 	    sizeof(hdr) - sizeof(hdr.magic), fp);
 	if (amt_read != sizeof(hdr) - sizeof(hdr.magic)) {
@@ -273,7 +277,7 @@ pcap_check_header(bpf_u_int32 magic, FILE *fp, u_int precision, char *errbuf,
 	switch (precision) {
 
 	case PCAP_TSTAMP_PRECISION_MICRO:
-		if (magic == NSEC_TCPDUMP_MAGIC) {
+		if (magic_int == NSEC_TCPDUMP_MAGIC) {
 			/*
 			 * The file has nanoseconds, the user
 			 * wants microseconds; scale the
@@ -290,7 +294,7 @@ pcap_check_header(bpf_u_int32 magic, FILE *fp, u_int precision, char *errbuf,
 		break;
 
 	case PCAP_TSTAMP_PRECISION_NANO:
-		if (magic == NSEC_TCPDUMP_MAGIC) {
+		if (magic_int == NSEC_TCPDUMP_MAGIC) {
 			/*
 			 * The file has nanoseconds, the
 			 * user wants nanoseconds; nothing to do.
@@ -344,7 +348,7 @@ pcap_check_header(bpf_u_int32 magic, FILE *fp, u_int precision, char *errbuf,
 		break;
 	}
 
-	if (magic == KUZNETZOV_TCPDUMP_MAGIC) {
+	if (magic_int == KUZNETZOV_TCPDUMP_MAGIC) {
 		/*
 		 * XXX - the patch that's in some versions of libpcap
 		 * changes the packet header but not the magic number,