Extcap: Create our fifo in a temporary directory.

Instead of creating a temp file, unlinking it, and creating a fifo with
the same name, add create_tempdir() so that we can create a temporary
directory and create a fifo inside that.

This should avoid a race condition in Carbon Black Cloud antivirus,
which if the timing is right, will stat the initial temporary *file*,
miss the fact that it's been replaced with a *fifo*, and open and steal
data^W^W read from it, leaving dumpcap to contend with the truncated
remains.

Adding the unexpected magic number to cap_pipe_open_live()'s error
message helped to debug this. Leave it in since it's handy to have in
that case.

Ping #15587

1 files changed, 1 insertions, 1 deletions

diff --git a/dumpcap.c b/dumpcap.c
index 5ac209015e..e09f27d59d 100644
--- a/dumpcap.c
+++ b/dumpcap.c
@@ -1850,7 +1850,7 @@ cap_pipe_open_live(char *pipename,
         /* Not a pcapng file, and either not a pcap type we know about
            or not a pcap file, either. */
         snprintf(errmsg, (gulong)errmsgl,
-                   "Data written to the pipe is neither in a supported pcap format nor in pcapng format.");
+                   "File type is neither a supported pcap nor pcapng format. (magic = 0x%08x)", magic);
         snprintf(secondary_errmsg, (gulong)secondary_errmsgl, "%s",
                    not_our_bug);
         goto error;