linux-kernel - Re: [PATCH v2 7/8] exec: Generic execfd support

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <874ksaioc6.fsf@x220.int.ebiederm.org>
Date:   Wed, 20 May 2020 11:05:29 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Rob Landley <rob@...dley.net>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        linux-fsdevel@...r.kernel.org, Al Viro <viro@...IV.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Casey Schaufler <casey@...aufler-ca.com>,
        linux-security-module@...r.kernel.org,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH v2 7/8] exec: Generic execfd support

Rob Landley <rob@...dley.net> writes:

> On 5/18/20 7:33 PM, Eric W. Biederman wrote:
>> 
>> Most of the support for passing the file descriptor of an executable
>> to an interpreter already lives in the generic code and in binfmt_elf.
>> Rework the fields in binfmt_elf that deal with executable file
>> descriptor passing to make executable file descriptor passing a first
>> class concept.
>
> I was reading this to try to figure out how to do execve(NULL, argv[], envp) to
> re-exec self after a vfork() in a chroot with no /proc, and hit the most trivial
> quibble ever:

We have /proc/self/exe today.  If I understand you correctly you would
like to do the equivalent of 'execve("/proc/self/exe", argv[], envp[])'
without having proc mounted.

The file descriptor is stored in mm->exe_file.

Probably the most straight forward implementation is to allow
execveat(AT_EXE_FILE, ...).

You can look at binfmt_misc for how to reopen an open file descriptor.

>> --- a/fs/exec.c
>> +++ b/fs/exec.c
>> @@ -1323,7 +1323,10 @@ int begin_new_exec(struct linux_binprm * bprm)
>>  	 */
>>  	set_mm_exe_file(bprm->mm, bprm->file);
>>  
>> +	/* If the binary is not readable than enforce mm->dumpable=0 */
>
> then

It took me a minute yes good catch.

Eric