pcap_io: introduce init_once helper that is called with priviledges

When using netsniff-ng with dropping priviledges, we have to introduce
another pcap helper function that is called once before we drop the
priviledges. In this function we have to invoke the disc I/O scheduler
policy, because it needs priviledges. Otherwise netsniff-ng will fail
with "Failed to set io prio for pid" on startup, since we're not root
anymore.

Reported-by: Doug Burks <doug.burks@gmail.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/pcap_mm.c b/pcap_mm.c
index f3b3fd0..28b0469 100644
--- a/pcap_mm.c
+++ b/pcap_mm.c
@@ -148,10 +148,13 @@ static void __pcap_mm_prepare_access_rd(int fd)
 	ptr_va_curr = ptr_va_start + sizeof(struct pcap_filehdr);
 }
 
-static int pcap_mm_prepare_access(int fd, enum pcap_mode mode, bool jumbo)
+static void pcap_mm_init_once(void)
 {
 	set_ioprio_be();
+}
 
+static int pcap_mm_prepare_access(int fd, enum pcap_mode mode, bool jumbo)
+{
 	switch (mode) {
 	case PCAP_MODE_RD:
 		__pcap_mm_prepare_access_rd(fd);
@@ -187,6 +190,7 @@ static void pcap_mm_prepare_close(int fd, enum pcap_mode mode)
 }
 
 const struct pcap_file_ops pcap_mm_ops = {
+	.init_once_pcap = pcap_mm_init_once,
 	.pull_fhdr_pcap = pcap_generic_pull_fhdr,
 	.push_fhdr_pcap = pcap_generic_push_fhdr,
 	.prepare_access_pcap = pcap_mm_prepare_access,