Change in titan.TestPorts.AF_PACKET[master]: guard against race between socket(AF_PACKET) and bind()

[laforge]

laforge has submitted this change. ( https://gerrit.osmocom.org/c/titan.TestPorts.AF_PACKET/+/21664 )

Change subject: guard against race between socket(AF_PACKET) and bind()
......................................................................

guard against race between socket(AF_PACKET) and bind()

An AF_PACKET socket will immediately receive packets of _all_ interfaces
until it is bound to one specific interface.  This introduces a race
condition between the socket() and the bind() syscall.

Let's use the ifindex passed for each packet in recvmsg() to drop
any packets received for other interfaces.

Change-Id: Icd0b23eb1d6f75ca3a05e5dd1a569fa389903fdf
---
M src/AF_PACKET_PT.cc
1 file changed, 10 insertions(+), 1 deletion(-)

Approvals:
  laforge: Looks good to me, approved; Verified



diff --git a/src/AF_PACKET_PT.cc b/src/AF_PACKET_PT.cc
index 3f46216..aa2def6 100644
--- a/src/AF_PACKET_PT.cc
+++ b/src/AF_PACKET_PT.cc
@@ -118,14 +118,23 @@
 		return;
 
 	if (is_readable) {
+		struct sockaddr_ll sll;
+		socklen_t sll_len = sizeof(sll);
 		int rc;
 
-		rc = read(fd, mRxBuf, sizeof(mRxBuf));
+		rc = recvfrom(fd, mRxBuf, sizeof(mRxBuf), 0, (struct sockaddr *)&sll, &sll_len);
 		if (rc < 0)
 			TTCN_error("Error reading from socket: %s", strerror(errno));
 		if (rc == 0)
 			TTCN_error("Dead socket: %s", strerror(errno));
 
+		/* ignore any packets that we might have received for a different interface, between
+		 * the socket() and the bind() call */
+		if (sll.sll_ifindex != mIfindex)
+			return;
+
+		/* TODO: report the other meta-data fields like sll_pkttype via the port */
+
 		incoming_message(AF__PACKET__Unitdata(OCTETSTRING(rc, mRxBuf)));
 	}
 }

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Gerrit-Project: titan.TestPorts.AF_PACKET
Gerrit-Branch: master
Gerrit-Change-Id: Icd0b23eb1d6f75ca3a05e5dd1a569fa389903fdf
Gerrit-Change-Number: 21664
Gerrit-PatchSet: 2
Gerrit-Owner: laforge <laforge at osmocom.org>
Gerrit-Reviewer: laforge <laforge at osmocom.org>
Gerrit-MessageType: merged
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