UID|EUID variables lose their ro properties

[mike b]

Hi!

Below is some odd stuff I recently noticed, looks to me as a bug, though
it's better if smarter people than me look at it as well to confirm that.
:)

Configuration Information:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64'
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-unknown-linux-gnu'
-DCONF_VENDOR='unknown' -DLOCALEDIR='/root/git_repos/bash/out/share/locale'
-DPACKAGE='bash' -DSHELL -DHAVE_CONFIG_H   -I.  -I. -I./include -I./lib
-g -O2 -Wno-parentheses -Wno-format-security
uname output: Linux test 3.16.0-4-amd64 #1 SMP Debian 3.16.36-1+deb8u2
(2016-10-19) x86_64 GNU/Linux
Machine Type: x86_64-unknown-linux-gnu

Bash Version: 4.4
Patch Level: 12
Release Status: release

Description:
        Whenever UID|EUID are exported to the env of newly exec Bash
        instance said variables lose their ro properties. Here's example:

                #!/bin/bash

                if (( ! UID )) \
                && (( ! EUID )) ; then
                        printf 'I am root (%u)\n' "$UID"
                        # at this point, you can change UID|EUID to whatever
                        # you like
                        UID=BANANA
                        EUID=PEANUTS
                        printf 'UID=%s\nEUID=%s\n' "$UID" "$EUID"
                        exit
                else
                        printf 'I am %u, not root\n' "$UID"
                fi
                export UID EUID
                exec bash -c "UID=0 EUID=0 $0"

        Here's example of an output:
                $ ./test
                I am 1000, not root
                I am root (0)
                UID=BANANA
                EUID=PEANUTS
        To my understanding, those variables should not be changed at any
        point, just like e.g. PPID (which is not affected by the above).
Regards,
Michal