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selinux: Use auth_read_passwd() interface for all our getpwnam() needs

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If passt or pasta are started as root, we need to read the passwd file
(be it /etc/passwd or whatever sssd provides) to find out UID and GID
of 'nobody' so that we can switch to it.

Instead of a bunch of allow rules for passwd_file_t and sssd macros,
use the more convenient auth_read_passwd() interface which should
cover our usage of getpwnam().

The existing rules weren't actually enough:

  # strace -e openat passt -f
  [...]
  Started as root, will change to nobody.
  openat(AT_FDCWD, "/etc/nsswitch.conf", O_RDONLY|O_CLOEXEC) = 4
  openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 4
  openat(AT_FDCWD, "/lib64/libnss_sss.so.2", O_RDONLY|O_CLOEXEC) = 4
  openat(AT_FDCWD, "/var/lib/sss/mc/passwd", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
  openat(AT_FDCWD, "/var/lib/sss/mc/passwd", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
  openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 4

with corresponding SELinux warnings logged in audit.log.

Reported-by: Minxi Hou <mhou@redhat.com>
Analysed-by: Miloš Malik <mmalik@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio 2024-11-14 23:48:54 +01:00
parent 6e1e44293e
commit 5e24466677
2 changed files with 2 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
contrib/selinux/passt.te
View File

@ -47,8 +47,6 @@ require {
type port_t;
type http_port_t;
type passwd_file_t;
class netlink_route_socket { bind create nlmsg_read };
type sysctl_net_t;
@ -96,8 +94,7 @@ allow passt_t self:capability { sys_tty_config setpcap net_bind_service setuid s
allow passt_t self:cap_userns { setpcap sys_admin sys_ptrace };
allow passt_t self:user_namespace create;
allow passt_t passwd_file_t:file read_file_perms;
sssd_search_lib(passt_t)
auth_read_passwd(passt_t)
allow passt_t proc_net_t:file read;
allow passt_t net_conf_t:file { open read };

9
contrib/selinux/pasta.te
View File

@ -68,9 +68,6 @@ require {
type system_dbusd_t;
type systemd_hostnamed_t;
type systemd_systemctl_exec_t;
type passwd_file_t;
type sssd_public_t;
type sssd_var_lib_t;
class dbus send_msg;
class system module_request;
class system status;
@ -115,8 +112,7 @@ allow pasta_t self:capability { setpcap net_bind_service sys_tty_config dac_read
allow pasta_t self:cap_userns { setpcap sys_admin sys_ptrace net_admin net_bind_service };
allow pasta_t self:user_namespace create;
allow pasta_t passwd_file_t:file read_file_perms;
sssd_search_lib(pasta_t)
auth_read_passwd(pasta_t)
domain_auto_trans(pasta_t, bin_t, unconfined_t);
domain_auto_trans(pasta_t, shell_exec_t, unconfined_t);
@ -178,12 +174,9 @@ allow pasta_t init_t:system status;
allow pasta_t unconfined_t:dir search;
allow pasta_t unconfined_t:file read;
allow pasta_t unconfined_t:lnk_file read;
allow pasta_t passwd_file_t:file { getattr open read };
allow pasta_t self:process { setpgid setcap };
allow pasta_t shell_exec_t:file { execute execute_no_trans map };
allow pasta_t sssd_var_lib_t:dir search;
allow pasta_t sssd_public_t:dir search;
allow pasta_t hostname_exec_t:file { execute execute_no_trans getattr open read map };
allow pasta_t system_dbusd_t:unix_stream_socket connectto;
allow pasta_t system_dbusd_t:dbus send_msg;