BUG #17953: Libpq can stall indefinitely with non-tls localhost (127.0.0.1) connection

The following bug has been logged on the website:

Bug reference: 17953
Logged by: Olli Pekkola
Email address: olli(dot)pekkola(at)grundium(dot)com
PostgreSQL version: 14.6
Operating system: Linux
Description:

I can craft a POC if neccessary, precise steps are not super clear at this
time. But the PQexecFinish() stalled several times withtout TLS with the
following stack (with TLS, not a single instance of this is observed):

#0 0x00007fd96e33f3ff in poll () from
target:/lib/x86_64-linux-gnu/libc.so.6
#1 0x0000561c06fdbed2 in poll ()
#2 0x0000561c07664bf0 in pqSocketPoll (end_time=-1, forWrite=0, forRead=1,
sock=<optimized out>) at
src/postgresql-14.6/src/interfaces/libpq/fe-misc.c:1134
#3 pqSocketCheck (conn=conn(at)entry=0x619000003780, forRead=forRead(at)entry=1,
forWrite=forWrite(at)entry=0, end_time=end_time(at)entry=-1) at
src/interfaces/libpq/fe-misc.c:1075
#4 0x0000561c07665320 in pqWaitTimed (forRead=forRead(at)entry=1,
forWrite=forWrite(at)entry=0, conn=conn(at)entry=0x619000003780,
finish_time=finish_time(at)entry=-1)
at src/postgresql-14.6/src/interfaces/libpq/fe-misc.c:1007
#5 0x0000561c0766536c in pqWait (forRead=forRead(at)entry=1,
forWrite=forWrite(at)entry=0, conn=conn(at)entry=0x619000003780) at
src/interfaces/libpq/fe-misc.c:992
#6 0x0000561c07663048 in PQgetResult (conn=0x619000003780) at
src/interfaces/libpq/fe-exec.c:2042
#7 PQgetResult (conn=0x619000003780) at src/interfaces/libpq/fe-exec.c:2007