iw: handle positive error codes gracefully

Commit Message

Brian Norris Nov. 3, 2020, 11:56 p.m. UTC

netlink(7) requires error codes to be negative, but since when does a
man page stop anyone? At a minimum, we shouldn't allow a non-conforming
vendor command to put us into an infinite loop in the below snippets
from __handle_cmd():

	err = 1;

	nl_cb_err(cb, NL_CB_CUSTOM, error_handler, &err);
...
	while (err > 0)
		nl_recvmsgs(state->nl_sock, cb);

Signed-off-by: Brian Norris <[e-mail]>
---
 iw.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

Patch

diff --git a/iw.c b/iw.c
index da71617921d8..35308ba3244a 100644
--- a/iw.c
+++ b/iw.c
@@ -287,7 +287,19 @@  static int error_handler(struct sockaddr_nl *nla, struct nlmsgerr *err,
 	int *ret = arg;
 	int ack_len = sizeof(*nlh) + sizeof(int) + sizeof(*nlh);
 
-	*ret = err->error;
+	if (err->error > 0) {
+		/*
+		 * This is illegal, per netlink(7), but not impossible (think
+		 * "vendor commands"). Callers really expect negative error
+		 * codes, so make that happen.
+		 */
+		fprintf(stderr,
+			"ERROR: received positive netlink error code %d\n",
+			err->error);
+		*ret = -EPROTO;
+	} else {
+		*ret = err->error;
+	}
 
 	if (!(nlh->nlmsg_flags & NLM_F_ACK_TLVS))
 		return NL_STOP;