From: Dmitry V. Levin <ldv@altlinux.org>
Date: Mon, 17 Apr 2017 04:37:41 +0000 (+0000)
Subject: netlink: decode NLMSG_ERROR messages
X-Git-Tag: v4.17~74
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=1be0e27b0bb30a23a597b6d5c2b68e13c657650b;p=strace

netlink: decode NLMSG_ERROR messages

* netlink.c (decode_nlmsgerr, decode_payload): New functions.
(decode_nlmsghdr_with_payload): Use decode_payload.
* tests/netlink_protocol.c (send_query): Check decoding
of NLMSG_ERROR messages.
* NEWS: Mention this change.
---

diff --git a/NEWS b/NEWS
index ba3e36a2..12cc5932 100644
--- a/NEWS
+++ b/NEWS
@@ -20,6 +20,7 @@ Noteworthy changes in release ?.?? (????-??-??)
   * Implemented decoding of statx syscall.
   * Implemented decoding of NS_* ioctl commands.
   * Implemented decoding of the remaining V4L2_BUF_TYPE_* types.
+  * Implemented decoding of NLMSG_ERROR netlink messages.
   * Updated lists of ioctl commands from Linux 4.11.
 
 * Bug fixes
diff --git a/netlink.c b/netlink.c
index dcd24629..16550d6c 100644
--- a/netlink.c
+++ b/netlink.c
@@ -69,6 +69,55 @@ print_nlmsghdr(struct tcb *tcp, const struct nlmsghdr *const nlmsghdr)
 		nlmsghdr->nlmsg_pid);
 }
 
+static void
+decode_nlmsghdr_with_payload(struct tcb *const tcp,
+			     const struct nlmsghdr *const nlmsghdr,
+			     const kernel_ulong_t addr,
+			     const kernel_ulong_t len);
+
+static void
+decode_nlmsgerr(struct tcb *const tcp,
+	       kernel_ulong_t addr,
+	       kernel_ulong_t len)
+{
+	struct nlmsgerr err;
+
+	if (umove_or_printaddr(tcp, addr, &err.error))
+		return;
+
+	tprints("{error=");
+	if (err.error < 0 && (unsigned) -err.error < nerrnos) {
+		tprintf("-%s", errnoent[-err.error]);
+	} else {
+		tprintf("%d", err.error);
+	}
+
+	addr += offsetof(struct nlmsgerr, msg);
+	len -= offsetof(struct nlmsgerr, msg);
+
+	if (len) {
+		tprints(", msg=");
+		if (fetch_nlmsghdr(tcp, &err.msg, addr, len)) {
+			decode_nlmsghdr_with_payload(tcp, &err.msg, addr, len);
+		}
+	}
+
+	tprints("}");
+}
+
+static void
+decode_payload(struct tcb *const tcp,
+	       const struct nlmsghdr *const nlmsghdr,
+	       const kernel_ulong_t addr,
+	       const kernel_ulong_t len)
+{
+	if (nlmsghdr->nlmsg_type == NLMSG_ERROR && len >= sizeof(int)) {
+		decode_nlmsgerr(tcp, addr, len);
+	} else {
+		printstrn(tcp, addr, len);
+	}
+}
+
 static void
 decode_nlmsghdr_with_payload(struct tcb *const tcp,
 			     const struct nlmsghdr *const nlmsghdr,
@@ -83,9 +132,8 @@ decode_nlmsghdr_with_payload(struct tcb *const tcp,
 		nlmsghdr->nlmsg_len > len ? len : nlmsghdr->nlmsg_len;
 	if (nlmsg_len > NLMSG_HDRLEN) {
 		tprints(", ");
-
-		printstrn(tcp, addr + NLMSG_HDRLEN,
-			  nlmsg_len - NLMSG_HDRLEN);
+		decode_payload(tcp, nlmsghdr, addr + NLMSG_HDRLEN,
+					 nlmsg_len - NLMSG_HDRLEN);
 	}
 
 	tprints("}");
diff --git a/tests/netlink_protocol.c b/tests/netlink_protocol.c
index 34e114be..03cff929 100644
--- a/tests/netlink_protocol.c
+++ b/tests/netlink_protocol.c
@@ -1,7 +1,7 @@
 /*
  * Check decoding of netlink protocol.
  *
- * Copyright (c) 2014-2016 Dmitry V. Levin <ldv@altlinux.org>
+ * Copyright (c) 2014-2017 Dmitry V. Levin <ldv@altlinux.org>
  * Copyright (c) 2016 Fabien Siron <fabien.siron@epita.fr>
  * All rights reserved.
  *
@@ -199,6 +199,124 @@ send_query(const int fd)
 	printf(", ...], %u, MSG_DONTWAIT, NULL, 0) = %s\n", msg_len, errstr);
 }
 
+static void
+test_nlmsgerr(const int fd)
+{
+	struct nlmsgerr *err;
+	struct nlmsghdr *nlh;
+	void *const nlh0 = tail_alloc(NLMSG_HDRLEN);
+	long rc;
+
+	/* error message without enough room for the error code */
+	nlh = nlh0;
+	nlh->nlmsg_len = NLMSG_HDRLEN + 4;
+	nlh->nlmsg_type = NLMSG_ERROR;
+	nlh->nlmsg_flags = NLM_F_REQUEST;
+	nlh->nlmsg_seq = 0;
+	nlh->nlmsg_pid = 0;
+
+	rc = sendto(fd, nlh, nlh->nlmsg_len, MSG_DONTWAIT, NULL, 0);
+	printf("sendto(%d, {{len=%u, type=NLMSG_ERROR, flags=NLM_F_REQUEST"
+	       ", seq=0, pid=0}, %p}, %u, MSG_DONTWAIT, NULL, 0) = %s\n",
+	       fd, nlh->nlmsg_len, nlh0 + NLMSG_HDRLEN,
+	       nlh->nlmsg_len, sprintrc(rc));
+
+	nlh = nlh0 - 2;
+	nlh->nlmsg_len = NLMSG_HDRLEN + 2;
+	nlh->nlmsg_type = NLMSG_ERROR;
+	nlh->nlmsg_flags = NLM_F_REQUEST;
+	nlh->nlmsg_seq = 0;
+	nlh->nlmsg_pid = 0;
+	memcpy(NLMSG_DATA(nlh), "42", 2);
+
+	rc = sendto(fd, nlh, nlh->nlmsg_len, MSG_DONTWAIT, NULL, 0);
+	printf("sendto(%d, {{len=%u, type=NLMSG_ERROR, flags=NLM_F_REQUEST"
+	       ", seq=0, pid=0}, \"42\"}, %u, MSG_DONTWAIT, NULL, 0) = %s\n",
+	       fd, nlh->nlmsg_len, nlh->nlmsg_len, sprintrc(rc));
+
+	/* error message with room for the error code only */
+	nlh = nlh0 - sizeof(err->error);
+	nlh->nlmsg_len = NLMSG_HDRLEN + sizeof(err->error);
+	nlh->nlmsg_type = NLMSG_ERROR;
+	nlh->nlmsg_flags = NLM_F_REQUEST;
+	nlh->nlmsg_seq = 0;
+	nlh->nlmsg_pid = 0;
+	err = NLMSG_DATA(nlh);
+	err->error = 42;
+
+	rc = sendto(fd, nlh, nlh->nlmsg_len, MSG_DONTWAIT, NULL, 0);
+	printf("sendto(%d, {{len=%u, type=NLMSG_ERROR, flags=NLM_F_REQUEST"
+	       ", seq=0, pid=0}, {error=42}}, %u, MSG_DONTWAIT, NULL, 0)"
+	       " = %s\n", fd, nlh->nlmsg_len, nlh->nlmsg_len, sprintrc(rc));
+
+	err->error = -1;
+
+	rc = sendto(fd, nlh, nlh->nlmsg_len, MSG_DONTWAIT, NULL, 0);
+	printf("sendto(%d, {{len=%u, type=NLMSG_ERROR, flags=NLM_F_REQUEST"
+	       ", seq=0, pid=0}, {error=-EPERM}}, %u, MSG_DONTWAIT, NULL, 0)"
+	       " = %s\n", fd, nlh->nlmsg_len, nlh->nlmsg_len, sprintrc(rc));
+
+	err->error = -32767;
+	nlh->nlmsg_len += sizeof(err->msg.nlmsg_len);
+
+	rc = sendto(fd, nlh, nlh->nlmsg_len, MSG_DONTWAIT, NULL, 0);
+	printf("sendto(%d, {{len=%u, type=NLMSG_ERROR, flags=NLM_F_REQUEST"
+	       ", seq=0, pid=0}, {error=-32767, msg=%p}}"
+	       ", %u, MSG_DONTWAIT, NULL, 0) = %s\n",
+	       fd, nlh->nlmsg_len, nlh0 + NLMSG_HDRLEN,
+	       nlh->nlmsg_len, sprintrc(rc));
+
+	/* error message with room for the error code and a header */
+	nlh = nlh0 - sizeof(*err);
+	nlh->nlmsg_len = NLMSG_HDRLEN + sizeof(*err);
+	nlh->nlmsg_type = NLMSG_ERROR;
+	nlh->nlmsg_flags = NLM_F_REQUEST;
+	nlh->nlmsg_seq = 0;
+	nlh->nlmsg_pid = 0;
+	err = NLMSG_DATA(nlh);
+	err->error = -13;
+	err->msg.nlmsg_len = NLMSG_HDRLEN;
+	err->msg.nlmsg_type = NLMSG_NOOP;
+	err->msg.nlmsg_flags = NLM_F_DUMP | NLM_F_REQUEST;
+	err->msg.nlmsg_seq = 42;
+	err->msg.nlmsg_pid = 1234;
+
+	rc = sendto(fd, nlh, nlh->nlmsg_len, MSG_DONTWAIT, NULL, 0);
+	printf("sendto(%d, {{len=%u, type=NLMSG_ERROR, flags=NLM_F_REQUEST"
+	       ", seq=0, pid=0}, {error=-EACCES"
+	       ", msg={{len=%u, type=NLMSG_NOOP, flags=NLM_F_REQUEST|0x%x"
+	       ", seq=%u, pid=%u}}}}, %u, MSG_DONTWAIT, NULL, 0) = %s\n",
+	       fd, nlh->nlmsg_len, err->msg.nlmsg_len, NLM_F_DUMP,
+	       err->msg.nlmsg_seq, err->msg.nlmsg_pid,
+	       nlh->nlmsg_len, sprintrc(rc));
+
+	/* error message with room for the error code, a header, and some data */
+	nlh = nlh0 - sizeof(*err) - 4;
+	nlh->nlmsg_len = NLMSG_HDRLEN + sizeof(*err) + 4;
+	nlh->nlmsg_type = NLMSG_ERROR;
+	nlh->nlmsg_flags = NLM_F_REQUEST;
+	nlh->nlmsg_seq = 0;
+	nlh->nlmsg_pid = 0;
+	err = NLMSG_DATA(nlh);
+	err->error = -13;
+	err->msg.nlmsg_len = NLMSG_HDRLEN + 4;
+	err->msg.nlmsg_type = NLMSG_NOOP;
+	err->msg.nlmsg_flags = NLM_F_DUMP | NLM_F_REQUEST;
+	err->msg.nlmsg_seq = 421;
+	err->msg.nlmsg_pid = 12345;
+	memcpy(NLMSG_DATA(&err->msg), "abcd", 4);
+
+	rc = sendto(fd, nlh, nlh->nlmsg_len, MSG_DONTWAIT, NULL, 0);
+	printf("sendto(%d, {{len=%u, type=NLMSG_ERROR, flags=NLM_F_REQUEST"
+	       ", seq=0, pid=0}, {error=-EACCES"
+	       ", msg={{len=%u, type=NLMSG_NOOP, flags=NLM_F_REQUEST|0x%x"
+	       ", seq=%u, pid=%u}, \"abcd\"}}}, %u, MSG_DONTWAIT, NULL, 0)"
+	       " = %s\n",
+	       fd, nlh->nlmsg_len, err->msg.nlmsg_len, NLM_F_DUMP,
+	       err->msg.nlmsg_seq, err->msg.nlmsg_pid,
+	       nlh->nlmsg_len, sprintrc(rc));
+}
+
 int main(void)
 {
 	struct sockaddr_nl addr;
@@ -227,6 +345,7 @@ int main(void)
 	free(path);
 
 	send_query(fd);
+	test_nlmsgerr(fd);
 
 	printf("+++ exited with 0 +++\n");