[pfx] Re: Feature request: let us configure /proc/net/if_inet6 path from config (or use alternative altogether)

Although I got it working inside Docker on my laptop. I am still not able
to get it to compile on an Android device because it doesn't have glibc.

Now your LD_PRELOAD solution looks more promising to me.

On Tue, Apr 14, 2026 at 10:17 PM Umair <[email protected]> wrote:

> I got it working. I managed to run make install successfully after running
> docker run. Attaching updated Dockerfile.
>
> On Tue, Apr 14, 2026 at 9:57 PM Umair <[email protected]> wrote:
>
>> I am attaching my Dockerfile.
>>
>> $docker run -it -w /postfix-3.11.1 --rm postfix:latest make install
>>
>> set -e; for i in src/util src/global src/dns src/tls src/xsasl src/master
>> src/milter src/postfix src/fsstone src/smtpstone src/sendmail src/error
>> src/pickup src/cleanup src/smtpd src/local src/trivial-rewrite src/qmgr
>> src/oqmgr src/smtp src/bounce src/pipe src/showq src/postalias src/postcat
>> src/postconf src/postdrop src/postkick src/postlock src/postlog src/postmap
>> src/postqueue src/postsuper src/qmqpd src/spawn src/flush src/verify
>> src/virtual src/proxymap src/anvil src/scache src/discard src/tlsmgr
>> src/postmulti src/postscreen src/dnsblog src/tlsproxy src/posttls-finger
>> src/postlogd src/nbdb_reindexd src/testing; do \
>>
>>  (set -e; echo "[$i]"; cd $i; make 'WARN=-Wmissing-prototypes -Wformat
>> -Wno-comment -fno-common' update MAKELEVEL=) || exit 1; \
>>
>> done
>>
>> sh: fatal: chdir /var/spool/postfix: No such file or directory
>>
>> make: *** [Makefile:95: update] Error 75
>>
>>
>>
>> /var/spool/postfix: No such file or directory
>>
>>
>> But when I try to create it during build it fails.
>>
>>
>> If I move the creation of these dirs just above the make command, it does
>> work but then docker run doesn't do anything. What am I missing?
>>
>>
>>
>> On Tue, Apr 14, 2026 at 9:20 PM Umair <[email protected]> wrote:
>>
>>> Normally my first thought is always to compile from source code and
>>> change the problematic part (the path in this case).
>>>
>>> Is there a docker image which downloads postfix source, install all the
>>> dependencies and builds and install postfix from source? This is what I am
>>> trying to achieve currently to get me the autonomy to change the source
>>> code as I please. I am currently stuck at permissions and missing files
>>> after the make. I figured I need to run make install from inside docker
>>> container and certain files need certain permissions, user and group.
>>>
>>> On Tue, Apr 14, 2026 at 7:22 PM Wietse Venema via Postfix-users <
>>> [email protected]> wrote:
>>>
>>>> Wietse Venema via Postfix-users:
>>>> > Maybe you can solve the root cause: fix the broken permission.
>>>> >
>>>> > Otherwise, consider running Postfix with an LD_PRELOAD as shown
>>>> below.
>>>> >
>>>> > /etc/ld.so.preload:
>>>> >     /etc/postfix/preload.so
>>>> >
>>>> > Where preload.so intercepts fopen(), inspects the argument, and
>>>> > then calls the real fopen().
>>>>
>>>> This has system-wide impact, i.e. it will affect every (native-code)
>>>> program, not just Postfix.
>>>>
>>>> The /etc/postfix/preload.so may not be appropriate for a system-wide
>>>> preload.
>>>>
>>>> You may want to test this in a VM first, otherwise you might end
>>>> up with an unusable system.
>>>>
>>>>         Wietse
>>>>
>>>> > Below is untested preload code. You may also have to redirect
>>>> > fopen64.
>>>> >
>>>> > The code was used in a system to police all libc calls that have a
>>>> > pathname argument.
>>>> >
>>>> >
>>>> https://www.ndss-symposium.org/ndss2010/where-do-you-want-go-today-escalating-privileges-pathname-manipulation/
>>>> >
>>>> >       Wietse
>>>> >
>>>> > /* preload.c  - build with: cc -fpic -shared -o preload.so preload.c
>>>> */
>>>> >
>>>> > #include <sys/types.h>
>>>> > #include <dlfcn.h>
>>>> > #include <stdio.h>
>>>> > #include <fcntl.h>
>>>> > #include <stdarg.h>
>>>> > #include <stdlib.h>
>>>> >
>>>> > static FILE *(*_real_fopen) (const char *, const char *);
>>>> >
>>>> > /* fopen - redirect /proc/net/if_inet6" to
>>>> "/etc/postfix/proc_inet_if_inet6" */
>>>> >
>>>> > FILE   *fopen(const char *path, const char *mode)
>>>> > {
>>>> >     if (path == "/proc/net/if_inet6")
>>>> >       path = "/etc/postfix/proc_inet_if_inet6";
>>>> >     if (_real_fopen == 0)
>>>> >       _real_fopen = (FILE *(*) (const char *, const char *))
>>>> >           dlsym(RTLD_NEXT, "fopen");
>>>> >     if (_real_fopen == 0) {
>>>> >       perror("dlsym(\"fopen\")");
>>>> >       return (0);
>>>> >     }
>>>> >     return _real_fopen(path, mode);
>>>> > }
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>>>> >
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>>>>
>>>

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