Re: [Qemu-devel] [PATCH] linux-user: allow to use sudo in guest

[Laurent Vivier <Laurent@vivier.eu>]

Le mercredi 02 janvier 2013 à 01:16 +0000, Peter Maydell a écrit :
> On 20 December 2012 20:56, Laurent Vivier <laurent@vivier.eu> wrote:
> > When qemu-linux-user is used in a linux container or chroot,
> > if it needs to load binaries with SUID/SGID bits, it needs to
> > have root rights to be able to change UID/GID. To do that, we
> > need to install it with SUID bits and root owner.
> 
> I suspect a suid qemu binary is a big fat security hole...

This is why this feature is disabled by default and must be enabled with
configure. Moreover this is only for qemu-linux-user and the first thing
done in main() is to set euid/egid to real uid/gid.

> > Then, if the SUID bit is not set on the binary to load,
> > qemu will set its UID to the saved UID (the current user ID).
> >
> > To be able to retrieve unsecure environment variables (LD_PRELOAD,
> > LD_LIBRARY_PATH) with SUID bit, we need to disable "unsetenv()".
> > Otherwise libc unsets these variables before entering in main()
> 
> This is basically deliberately disabling a glibc security check.

Yes, but this security check is mainly to avoid to load unsecure
library. To avoid this too, we force the "--static" mode. This is not
perfect but bring to qemu-linux-user an interesting feature.

> Needs careful thought and review (which I don't have time for
> just now I'm afraid) before this can be committed.
> 
> -- PMM

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