[openwrt/openwrt] procd: make mDNS TXT record parsing more solid

[LEDE Commits]

ansuel pushed a commit to openwrt/openwrt.git, branch openwrt-23.05:
https://git.openwrt.org/2541ff391fc88d2fc378c4fa9374f8b1a3e4e9b9

commit 2541ff391fc88d2fc378c4fa9374f8b1a3e4e9b9
Author: Christian Marangi <ansuelsmth at gmail.com>
AuthorDate: Mon Apr 29 21:17:31 2024 +0200

    procd: make mDNS TXT record parsing more solid
    
    mDNS broadcast can't accept empty TXT record and would fail
    registration.
    
    Current procd_add_mdns_service checks only if the first passed arg is
    empty but don't make any verification on the other args permittins
    insertion of empty values in TXT record.
    
    Example:
    
            procd_add_mdns "blah" \
                                    "tcp" "50" \
                                    "1" \
                                    "" \
                                    "3"
    
    Produce:
    
    { "blah_50": { "service": "_blah._tcp.local", "port": 50, "txt": [ "1", "", "3" ] } }
    
    The middle empty TXT record should never be included as it's empty.
    
    This can happen with scripts that make fragile parsing and include
    variables even if they are empty.
    
    Prevent this and make the TXT record more solid by checking every
    provided TXT record and include only the non-empty ones.
    
    The fixed JSON is the following:
    
    { "blah_50": { "service": "_blah._tcp.local", "port": 50, "txt": [ "1", "3" ] } }
    
    Fixes: b0d9dcf84dd0 ("procd: update to latest git HEAD")
    Reported-by: Paul Donald <newtwen at gmail.com>
    Link: https://github.com/openwrt/openwrt/pull/15331
    Signed-off-by: Christian Marangi <ansuelsmth at gmail.com>
    (cherry picked from commit 4b043047132de0b3d90619d538f103af6153fa5a)
---
 package/system/procd/files/procd.sh | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/package/system/procd/files/procd.sh b/package/system/procd/files/procd.sh
index 5148b2f03c..d834fa601a 100644
--- a/package/system/procd/files/procd.sh
+++ b/package/system/procd/files/procd.sh
@@ -570,18 +570,21 @@ _procd_set_config_changed() {
 }
 
 procd_add_mdns_service() {
-	local service proto port
+	local service proto port txt_count=0
 	service=$1; shift
 	proto=$1; shift
 	port=$1; shift
 	json_add_object "${service}_$port"
 	json_add_string "service" "_$service._$proto.local"
 	json_add_int port "$port"
-	[ -n "$1" ] && {
-		json_add_array txt
-		for txt in "$@"; do json_add_string "" "$txt"; done
-		json_select ..
-	}
+	for txt in "$@"; do
+		[ -z "$txt" ] && continue
+		txt_count=$((txt_count+1))
+		[ $txt_count -eq 1 ] && json_add_array txt
+		json_add_string "" "$txt"
+	done
+	[ $txt_count -gt 0 ] && json_select ..
+
 	json_select ..
 }