[PATCH] Fix leak in getaddrinfo introduced by the fix for CVE-2023-4806.

[Romain Geissler]

This patch fixes a very recently added leak in getaddrinfo (which was
backported on release branches too).

I didn't spend much more than 5 minutes on investigating the code to end
up with this patch, so it may be wrong. Quickly testing it on my side,
it seems to work for me, but it definitely needs review from people who
actually know this part of the code ;)

Running a stripped down version of the newly added test
nss/nss_test_gai_hv2_canonname.c with valgrind results in exposure of
the leak:

> cat test.c

int main()
{
    char aHostName[256];
    gethostname(aHostName,255);

    struct addrinfo hints = {};
    struct addrinfo *result = NULL;

    hints.ai_family = AF_INET6;
    hints.ai_flags = AI_ALL | AI_V4MAPPED | AI_CANONNAME;

    int ret = getaddrinfo(aHostName, NULL, &hints, &result);

    if (ret != 0)
        return 1;
    freeaddrinfo(result);
    return 0;
}

> /opt/1A/toolchain/x86_64-v19/bin/gcc -g -o test test.c
> /opt/1A/toolchain/x86_64-v19/build-pack/default/bin/valgrind --leak-check=full ./test
   ... (snapped)
==68017== 37 bytes in 1 blocks are definitely lost in loss record 1 of 1
==68017==    at 0x4840745: malloc (in /remote/tools/Linux/2.6/1A/toolchain/x86_64-v19.0.81/build-pack/19.0.81.0/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==68017==    by 0x48E7CDA: strdup (in /remote/tools/Linux/2.6/1A/toolchain/x86_64-v19.0.81/lib/libc.so.6)
==68017==    by 0x4936582: convert_hostent_to_gaih_addrtuple.isra.0 (in /remote/tools/Linux/2.6/1A/toolchain/x86_64-v19.0.81/lib/libc.so.6)
==68017==    by 0x4936787: gethosts (in /remote/tools/Linux/2.6/1A/toolchain/x86_64-v19.0.81/lib/libc.so.6)
==68017==    by 0x4938F37: getaddrinfo (in /remote/tools/Linux/2.6/1A/toolchain/x86_64-v19.0.81/lib/libc.so.6)
==68017==    by 0x4011A5: main (test.c:17)
   ... (snapped)
---
 sysdeps/posix/getaddrinfo.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/sysdeps/posix/getaddrinfo.c b/sysdeps/posix/getaddrinfo.c
index b4e8ea3880a..5f5bc3fd51f 100644
--- a/sysdeps/posix/getaddrinfo.c
+++ b/sysdeps/posix/getaddrinfo.c
@@ -1199,6 +1199,7 @@ free_and_return:
   if (res.free_at)
     free (res.at);
   free (res.canon);
+  free (res.h_name);
 
   return result;
 }
-- 
2.39.3