Package: postfix
Version: 3.3.0-1
Severity: important
Tags: security

The /etc/network/if-*.d/postfix scripts contain:

if [ ! -x /sbin/resolvconf ]; then
        f=/etc/resolv.conf
        if ! cp $f $(postconf -hx queue_directory)$f 2>/dev/null; then
                exit 0
        fi

If two such scripts run concurrently (which is now possible), the two
"cp" commands can also run concurrently, with unexpected results on
the generated resolv.conf file for postfix.

It might be a security issue as a consequence is that an incorrect
DNS server could be used.

-- System Information:
Debian Release: buster/sid
  APT prefers unstable-debug
  APT policy: (500, 'unstable-debug'), (500, 'stable-updates'), (500, 
'unstable'), (500, 'testing'), (500, 'stable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 4.15.0-3-amd64 (SMP w/8 CPU cores)
Locale: LANG=POSIX, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=POSIX 
(charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages postfix depends on:
ii  adduser                3.117
ii  cpio                   2.12+dfsg-6
ii  debconf [debconf-2.0]  1.5.66
ii  dpkg                   1.19.0.5
ii  e2fsprogs              1.44.1-2
ii  libc6                  2.27-3
ii  libdb5.3               5.3.28-13.1+b1
ii  libicu57               57.1-9
ii  libsasl2-2             2.1.27~101-g0780600+dfsg-3.1
ii  libssl1.1              1.1.0h-2
ii  lsb-base               9.20170808
ii  netbase                5.4
ii  ssl-cert               1.0.39

Versions of packages postfix recommends:
ii  python3  3.6.5-3

Versions of packages postfix suggests:
ii  bsd-mailx [mail-reader]  8.1.2-0.20160123cvs-4
pn  dovecot-common           <none>
ii  emacs25 [mail-reader]    25.2+1-6+b1
ii  libsasl2-modules         2.1.27~101-g0780600+dfsg-3.1
ii  mutt [mail-reader]       1.9.5-2
pn  postfix-cdb              <none>
ii  postfix-doc              3.3.0-1
pn  postfix-ldap             <none>
pn  postfix-lmdb             <none>
pn  postfix-mysql            <none>
ii  postfix-pcre             3.3.0-1
pn  postfix-pgsql            <none>
ii  postfix-sqlite           3.3.0-1
ii  procmail                 3.22-26
pn  resolvconf               <none>
pn  sasl2-bin                <none>
pn  ufw                      <none>

-- debconf information excluded

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