git: 8646d65b4533 - main - hastd: Fix crash on empty message

The branch main has been updated by des:

URL: https://cgit.FreeBSD.org/src/commit/?id=8646d65b45339642d4aab1de35a2bc79fc45f09e

commit 8646d65b45339642d4aab1de35a2bc79fc45f09e
Author:     Glen Barber <gjb@FreeBSD.org>
AuthorDate: 2026-09-03 07:51:28 +0000
Commit:     Dag-Erling Smørgrav <des@FreeBSD.org>
CommitDate: 2026-09-03 07:58:54 +0000

    hastd: Fix crash on empty message
    
    A HAST message can be empty, in which case ebuf_add_tail() does nothing
    and ebuf_data() returns NULL because the size of the ebuf is zero, but
    hast_proto_recv_hdr() asserts that the return value is not NULL,
    resulting in an immediate crash if hastctl or hastd receive an empty
    message.  This is trivially reproducable by running `hastctl status` or
    `hastctl role init` (as the rc script does prior to stopping hastd).
    
    To avoid this, don't try to grow the ebuf or receive additional data
    if the header size is zero.
    
    PR:             298085
    MFC after:      3 days
    Reviewed by:    kevans, gjb
    Differential Revision:  https://reviews.freebsd.org/D59306
---
 sbin/hastd/hast_proto.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/sbin/hastd/hast_proto.c b/sbin/hastd/hast_proto.c
index d9f231e7b007..fc90bf59dc8a 100644
--- a/sbin/hastd/hast_proto.c
+++ b/sbin/hastd/hast_proto.c
@@ -150,12 +150,14 @@ hast_proto_recv_hdr(const struct proto_conn *conn, struct nv **nvp)
 	eb = ebuf_alloc(hdr.size);
 	if (eb == NULL)
 		goto fail;
-	if (ebuf_add_tail(eb, NULL, hdr.size) == -1)
-		goto fail;
-	hptr = ebuf_data(eb, NULL);
-	PJDLOG_ASSERT(hptr != NULL);
-	if (proto_recv(conn, hptr, hdr.size) == -1)
-		goto fail;
+	if (hdr.size > 0) {
+		if (ebuf_add_tail(eb, NULL, hdr.size) == -1)
+			goto fail;
+		hptr = ebuf_data(eb, NULL);
+		PJDLOG_ASSERT(hptr != NULL);
+		if (proto_recv(conn, hptr, hdr.size) == -1)
+			goto fail;
+	}
 	nv = nv_ntoh(eb);
 	if (nv == NULL)
 		goto fail;