git: 5f7ae464db5b - stable/12 - blacklistd: Handle 0 sized messages

The branch stable/12 has been updated by emaste:

URL: https://cgit.FreeBSD.org/src/commit/?id=5f7ae464db5bd1527a844c228afc269cedb6822c

commit 5f7ae464db5bd1527a844c228afc269cedb6822c
Author:     Ed Maste <emaste@FreeBSD.org>
AuthorDate: 2022-07-18 00:43:52 +0000
Commit:     Ed Maste <emaste@FreeBSD.org>
CommitDate: 2022-07-25 15:00:11 +0000

    blacklistd: Handle 0 sized messages
    
    Patch obtained from https://github.com/zoulasc/blocklist commit
    ada75856bc6fcabbdd25ffbe08fbad5cf2a2c08a
    
    PR:             264599
    MFC after:      1 week
    
    (cherry picked from commit b1e81e6ddee42efb0f0d49cfc6cebb48d52e3f08)
---
 contrib/blacklist/lib/bl.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/contrib/blacklist/lib/bl.c b/contrib/blacklist/lib/bl.c
index 9f93b91f4c8f..ab2bd7c43ebe 100644
--- a/contrib/blacklist/lib/bl.c
+++ b/contrib/blacklist/lib/bl.c
@@ -434,6 +434,7 @@ bl_recv(bl_t b)
 	} ub;
 	int got;
 	ssize_t rlen;
+	size_t rem;
 	bl_info_t *bi = &b->b_info;
 
 	got = 0;
@@ -504,10 +505,12 @@ bl_recv(bl_t b)
 		return NULL;
 	}
 
-	if ((size_t)rlen <= sizeof(ub.bl)) {
+	rem = (size_t)rlen;
+	if (rem < sizeof(ub.bl)) {
 		bl_log(b->b_fun, LOG_ERR, "message too short %zd", rlen);
 		return NULL;
 	}
+	rem -= sizeof(ub.bl);
 
 	if (ub.bl.bl_version != BL_VERSION) {
 		bl_log(b->b_fun, LOG_ERR, "bad version %d", ub.bl.bl_version);
@@ -521,7 +524,10 @@ bl_recv(bl_t b)
 	bi->bi_uid = -1;
 	bi->bi_gid = -1;
 #endif
-	strlcpy(bi->bi_msg, ub.bl.bl_data, MIN(sizeof(bi->bi_msg),
-	    ((size_t)rlen - sizeof(ub.bl) + 1)));
+	rem = MIN(sizeof(bi->bi_msg), rem);
+	if (rem == 0)
+		bi->bi_msg[0] = '\0';
+	else
+		strlcpy(bi->bi_msg, ub.bl.bl_data, rem);
 	return bi;
 }