ftpd: escape chroot prior to re-executing ls helper

When we merely chdir to saved "real" root fd,
exec("proc/self/exe") works for static executables but not
for dynamic ones (they can't find their interpreter).

With this patch, we also *chroot* to real root.
As a bonus, this gives us proper usernames, timezone conversion
etc.

function                                             old     new   delta
popen_ls                                             203     259     +56
ftpd_main                                           2362    2366      +4

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
ftpd: for LIST, open current directory *in the child*

Last change introduced an open fd leak. This is the fix.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
ftpd: do not use root_fd if we are not in chroot

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
stat: fix printing selinux context and null-dereference

busybox stat tries to always print the selinux context, even if it
is not requested which leads to a segmentation fault due to
dereferencing a null-pointer.

This also changes the format-string used to print the context to
so it actually produces useful output.

Signed-off-by: Michael Gernoth <michael@gernoth.net>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>