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selinux: Fix domain transitions for typical commands pasta might run

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...now it gets ugly. If we use pasta without an existing target
namespace, and run commands directly or spawn a shell, and keep
the pasta_t domain when we do, they won't be able to do much: a
shell might even start, but it's not going to be usable, or to
even display a prompt.

Ideally, pasta should behave like a shell when it spawns a command:
start as unconfined_t and automatically transition to whatever
domain is associated in the specific policy for that command. But
we can't run as unconfined_t, of course.

It would seem natural to switch to unconfined_t "just before", so
that the default transitions happen. But transitions can only happen
when we execvp(), and that's one single transition -- not two.

That is, this approach would work for:

  pasta -- sh -c 'ip address show'

but not for:

  pasta -- ip address show

If we configure a transition to unconfined_t when we run ip(8), we'll
really try to start that as unconfined_t -- but unconfined_t isn't
allowed as entrypoint for ip(8) itself, and execvp() will fail.

However, there aren't many different types of binaries pasta might
commonly run -- for example, we're unlikely to see pasta used to run
a mount(8) command.

Explicitly set up domain transition for common stuff -- switching to
unconfined_t for bin_t and shells works just fine, ip(8), ping(8),
arping(8) and similar need a different treatment.

While at it, allow commands we spawn to inherit resource limits and
signal masks, because that's what happens by default, and don't
require AT_SECURE sanitisation of the environment (because that
won't happen by default). Slightly unrelated: we also need to
explicitly allow pasta_t to use TTYs, not just PTYs, otherwise
we can't keep stdin and stdout open for shells.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio 2023-08-16 07:20:30 +02:00
parent 30817fdd4e
commit 0af928eaa0
1 changed files with 18 additions and 1 deletions
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19
contrib/selinux/pasta.te
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@ -51,6 +51,7 @@ require {
type tun_tap_device_t;
type sysctl_net_t;
class tun_socket create;
type user_tty_device_t;
attribute port_type;
type port_t;
@ -77,6 +78,12 @@ require {
type kernel_t;
class process setpgid;
type shell_exec_t;
type ifconfig_exec_t;
type netutils_exec_t;
type ping_exec_t;
type ifconfig_t;
type netutils_t;
type ping_t;
type init_t;
class capability { sys_tty_config setuid setgid };
@ -111,7 +118,12 @@ allow pasta_t self:user_namespace create;
allow pasta_t passwd_file_t:file read_file_perms;
sssd_search_lib(pasta_t)
allow pasta_t bin_t:file { execute execute_no_trans map };
domain_auto_trans(pasta_t, bin_t, unconfined_t);
domain_auto_trans(pasta_t, shell_exec_t, unconfined_t);
domain_auto_trans(pasta_t, ifconfig_exec_t, ifconfig_t);
domain_auto_trans(pasta_t, netutils_exec_t, netutils_t);
domain_auto_trans(pasta_t, ping_exec_t, ping_t);
allow pasta_t nsfs_t:file { open read };
allow pasta_t user_home_t:dir getattr;
@ -192,3 +204,8 @@ allow pasta_t nsfs_t:file read;
allow pasta_t net_conf_t:lnk_file read;
allow pasta_t proc_net_t:lnk_file read;
allow pasta_t unconfined_t:process { noatsecure rlimitinh siginh };
allow pasta_t ifconfig_t:process { noatsecure rlimitinh siginh };
allow pasta_t netutils_t:process { noatsecure rlimitinh siginh };
allow pasta_t ping_t:process { noatsecure rlimitinh siginh };
allow pasta_t user_tty_device_t:chr_file { append read write };