printf cannot write more than one line to /proc/pid/uid_map

[Kusanagi Kouichi]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' 
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-pc-linux-gnu' 
-DCONF_VENDOR='pc' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL 
-DHAVE_CONFIG_H   -I.  -I../. -I.././include -I.././lib  -D_FORTIFY_SOURCE=2 -g 
-O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat 
-Werror=format-security -Wall
uname output: Linux crescent 3.14.0-rc7 #1 SMP Mon Mar 17 07:17:51 UTC 2014 
x86_64 GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Bash Version: 4.3
Patch Level: 0
Release Status: release

Description:
        Bash's builtin printf cannot write more than one line to
        /proc/pid/uid_map because printf writes one line at a time
        and uid_map can be written only once.

Repeat-By:
        shell 1
        $ unshare -U
        $ echo $$
        31861

        shell 2
        # printf '0 0 1\n1 1 1' > /proc/31861/uid_map
        printf: write error: Operation not permitted