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

[Eduardo A . Bustamante López]

On Tue, Mar 25, 2014 at 08:24:13PM +0900, Kusanagi Kouichi wrote:
> 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.
I don't see why this is a bash bug though. printf works as
documented. The fact that the way it works is incompatible with this
/proc thing is *not* bash's fault. It just means that it's not
flexible enough to tell it to write all at once, but that's not a
bug.

> 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
> 

-- 
Eduardo Alan Bustamante López