Endless loop in /usr/lib/udev/udev-configure-printer

This happend today:

• cups server did not print anymore
• a client is looping in connect->fd->close->connect

Cause is unknown. Maybe the cups server hit a rate limit because it prints:

Flooding server log:

Dec 11 04:37:32 cupsserver kernel: STATE_INVALID_DROP: IN=ens32 OUT= MAC=xx SRC=<clientip> DST=<cupsserver> LEN=40 TOS=0x00 PREC=0x00 TTL=64 ID=51545 DF PROTO=TCP SPT=43770 DPT=631 WINDOW=0 RES=0x00 RST URGP=0

The client is in an endless loop, this flooded the server, which prints the above message until the HD ist full, then
cups does not print anymore.

The endless loop of the client straced, from connect->close->to connect again.

connect(5, {sa_family=AF_INET, sin_port=htons(631),sin_addr=inet_addr("cupsserver")}, 16) = -1 EINPROGRESS (Operation now in progress)
fcntl(5, F_SETFL, O_RDWR)               = 0
poll([{fd=5, events=POLLIN|POLLOUT}], 1, 250) = 1 ([{fd=5, revents=POLLOUT}])
getpeername(5, {sa_family=AF_INET, sin_port=htons(631),sin_addr=inet_addr(10.x.y.z)}, [256->16]) = 0
uname({sysname="Linux", nodename="client.linux", ...}) = 0
sendto(5, "OPTIONS * HTTP/1.1\r\nConnection: Upgrade\r\nHost: cupsserver.domain.de:631\r\nUpgrade: TLS/1.1,TLS/1.0\r\nUser-Agent: CUPS/1.6.3 (Linux 3.10.0-1160.80.1.el7.x86_64; x86_64) IPP/2.0\r\n\r\n", 173, 0, NULL, 0) =
poll([{fd=5, events=POLLIN}], 1, 60000) = 1 ([{fd=5, revents=POLLIN}])
recvfrom(5, "HTTP/1.1 101 Switching Protocols\r\nDate: Mon, 12 Dec 2022 09:19:10 GMT\r\nServer: CUPS/1.6 IPP/2.1\r\nConnection: Keep-Alive\r\nKeep-Alive: timeout=30\r\nContent-Language: en_US\r\nConnection: Upgrade\r\
sendto(5, "\26\3\1\1\20\1\0\1\f\...)"
recvfrom(5, "\26\3\3\0:\2\0", 7, 0, NULL, NULL) = 7
recvfrom(5, "\0006\3\3\3034\210\241\33f\302\367Q\2217\307iT\32\220n\325\\17\0\1\1", 56, 0, NULL, NULL) = 56
recvfrom(5, "\26\3\3\26\326", 5, 0, NULL, NULL) = 5
recvfrom(5, "\v\0\26\322\0\26\317\010\f\6Bayern1\0210\17\6\3U\4\7\f\10M...)
recvfrom(5, "\26\3\3\0\4", 5, 0, NULL, NULL) = 5
recvfrom(5, "\16\0\0\0", 4, 0, NULL, NULL) = 4
sendto(5, "\26\3\3\1\6\2...)"
recvfrom(5, "\26\3\3\0\252", 5, 0, NULL, NULL) = 5
recvfrom(5, "\4\0\0\246\0\0\1,\0\...")
recvfrom(5, "\24\3\3\0\1", 5, 0, NULL, NULL) = 5
recvfrom(5, "\1", 1, 0, NULL, NULL)     = 1
recvfrom(5, "\26\3\3\0(", 5, 0, NULL, NULL) = 5
recvfrom(5, "\230/\230\351\257\7\201h\237\347A\v\12e\27\376", 40, 0, NULL, NULL) = 40
poll([{fd=5, events=POLLIN}], 1, 60000) = 1 ([{fd=5, revents=POLLIN}])
recvfrom(5, "\27\3\3\0\306", 5, 0, NULL, NULL) = 5
recvfrom(5, "\230/\23...")
sendto(5, "...)
close(5)                                = 0
socket(AF_INET, SOCK_STREAM, IPPROTO_IP) = 5
setsockopt(5, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
setsockopt(5, SOL_SOCKET, SO_REUSEPORT, [1], 4) = 0
setsockopt(5, SOL_TCP, TCP_NODELAY, [1], 4) = 0
fcntl(5, F_SETFD, FD_CLOEXEC)           = 0
fcntl(5, F_GETFL)                       = 0x2 (flags O_RDWR)
fcntl(5, F_SETFL, O_RDWR|O_NONBLOCK)    = 0
connect(5, {sa_family=AF_INET, sin_port=htons(631),sin_addr=inet_addr("cupsserver")}, 16) = -1 EINPROGRESS (Operation now in progress)

When looking at the source code:

https://github.com/OpenPrinting/system-config-printer/blob/master/udev/udev-configure-printer.c

I dont see this loop, the pid is always the same, so its whithin this process.
The compiled version is from:

system-config-printer-1.4.8-2.el7.3.src.rpm

Which is rather old based on system-config-printer-1.4.1.tar.xz.

Restarting cups exited the client binary, no problem anymore.

The reason for the endless looping client is unknown.

Start with udev/udev-configure-printer.c and the system-config-printer-1.4.8-2.el7.3 source package; compare that source with the current repository code. Reproduce the connect/close cycle using the supplied strace and inspect behavior around a CUPS restart. Done means identifying a reproducible cause and validating a change that prevents the client from looping.