Potential Memory Leak in libc DNS Resolution Functions

[Charalampos Mitrodimas <charmitro@posteo.net>]

Hello,

I've encountered a potential memory leak in libc, specifically within
the DNS resolution functions, as identified by Valgrind. The leak
involves __libc_alloc_buffer_allocate and related functions. Here's the
Valgrind output snippet:

    ==4151== 156 bytes in 1 blocks are definitely lost in loss record 
730 of 1,029
    ==4151==    at 0x4848899: malloc (in 
/usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
    ==4151==    by 0x4D15048: __libc_alloc_buffer_allocate 
(alloc_buffer_allocate.c:26)
    ==4151==    by 0x4DBDC65: alloc_buffer_allocate (alloc_buffer.h:143)
    ==4151==    by 0x4DBDC65: __resolv_conf_allocate (resolv_conf.c:391)
    ==4151==    by 0x4DB8D0A: __resolv_conf_load (res_init.c:599)
    ==4151==    by 0x4DBD85E: __resolv_conf_get_current (resolv_conf.c:140)
    ==4151==    by 0x4DB9394: __res_vinit (res_init.c:628)
    ==4151==    by 0x4DBE82F: maybe_init (resolv_context.c:122)
    ==4151==    by 0x4DBE82F: context_get (resolv_context.c:184)
    ==4151==    by 0x4DBE82F: context_get (resolv_context.c:176)
    ==4151==    by 0x4DBE82F: __resolv_context_get (resolv_context.c:195)
    ==4151==    by 0x4D78C87: get_nss_addresses (getaddrinfo.c:617)
    ==4151==    by 0x4D78C87: gaih_inet (getaddrinfo.c:1179)
    ==4151==    by 0x4D78C87: getaddrinfo (getaddrinfo.c:2397)
    ==4151==    by 0x4A7108E: <std::sys_common::net::LookupHost as 
core::convert::TryFrom<(&str,u16)>>::try_from::{{closure}} (net.rs:207)
    ==4151==    by 0x4A6A105: <(&str,u16) as 
std::net::socket_addr::ToSocketAddrs>::to_socket_addrs 
(small_c_string.rs:43)
    ==4151==    by 0x495356A: 
lettre::transport::smtp::client::net::NetworkStream::connect::try_connect 
(net.rs:104)
    ==4151==    by 0x49532F1: 
lettre::transport::smtp::client::net::NetworkStream::connect (net.rs:139)

This issue arose in an application using Rust's email library Lettre,
ultimately traced back to libc during DNS resolution. Could you please
advise if this is a known issue and recommend any steps to address it?
I'm willing to contribute a fix, but want to make sure this is of
concern for the libc team, before starting the investigation.

Thank you for your support.

           Charalampos Mitrodimas