Re: Bug reporting

["Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>]

Hello,

On Fri, 7 May 2021 at 02:21, Dave Chupreev <cdn.dev@yandex.ru> wrote:
>
> Well I see, I've tried on Linux and yea I didn't find any option to insert multiple definitions.

I think the only way to insert multiple definitions is by direct
manipulation of 'extern char **environ'.

Thanks,

Michael


> 06.05.2021, 01:37, "Alejandro Colomar (man-pages)" <alx.manpages@gmail.com>:
>
> [ added a few CCs ]
>
> Hello Dave,
>
> On 5/5/21 10:30 PM, Dave Chupreev wrote:
>
>  Hello, Alejandro.
>
>  On page 138
>
>
> I guess you refer to TLPI, written by Michael.
>
>
>       1.
>
>          Your version of /unsetenv() /should check to see whether there
>          are multiple definitions of an environment variable, and remove
>          them all.
>
>  How can I add such variables which have many definitions? According to
>  *putenv* and *setenv* functions, variables with the same names are
>  replaced if encountered.
>
>
> I haven't read that part of the book yet, so I ignore the context. But
> AFAIK, that can't happen on Linux, as you pointed out (probably neither
> on Unix systems in general, but I don't know for sure, probably Michael
> does). I guess the only possibility is if an attacker somehow modified
> your environment and inserted multiple copies of an env variable.
>
> The book (TLPI) states that glibc does check that, so I digged into the
> sources and found that in <stdlib/setenv.c>, around line 290
> (<https://sourceware.org/git?p=glibc.git;a=blob;f=stdlib/setenv.c;h=893f081af6b5a21b999a4056757fd69d1386c0d4;hb=HEAD#l290>).
>  That behavior was introduced by Roland in commit
> 196980f5117c8d38f10d64bf67eeb0924651675f
> (<https://sourceware.org/git/?p=glibc.git;a=commit;h=196980f5117c8d38f10d64bf67eeb0924651675f>),
> so maybe he can better explain the reasons behind the change (the commit
> msg is quite unexplicative) if he still remembers (that goes back to 1995).
>
> Regards,
>
> Alex
>
> --
> Alejandro Colomar
> Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
> http://www.alejandro-colomar.es/



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/