cap_syslog: remove CAP_SYS_ADMIN when dmesg_restrict

CAP_SYSLOG was separated from CAP_SYS_ADMIN and introduced in Linux
2.6.37 (2010-11). For a long time, certain syslog actions required
CAP_SYS_ADMIN or CAP_SYSLOG. Maybe it’s time to officially remove
CAP_SYS_ADMIN for more fine-grained control.

CAP_SYS_ADMIN was once removed but added back for backwards
compatibility reasons. In commit 38ef4c2e437d ("syslog: check cap_syslog
when dmesg_restrict") (2010-12), CAP_SYS_ADMIN was no longer needed. And
in commit ee24aebffb75 ("cap_syslog: accept CAP_SYS_ADMIN for now")
(2011-02), it was accepted again. Since then, CAP_SYS_ADMIN has been
preserved.

Now that almost 13 years have passed, the legacy application may have
had enough time to be updated.

Signed-off-by: Jingzi Meng <mengjingzi@iie.ac.cn>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20240105062007.26965-1-mengjingzi@iie.ac.cn
Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index f2444b581e16c3c3b4ef955ab89c2a0278436f7b..1c6e7dfc4ba7941d1ea53e6e81538cab597ddadd 100644 (file)
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -598,17 +598,6 @@ static int check_syslog_permissions(int type, int source)
        if (syslog_action_restricted(type)) {
                if (capable(CAP_SYSLOG))
                        goto ok;
-               /*
-                * For historical reasons, accept CAP_SYS_ADMIN too, with
-                * a warning.
-                */
-               if (capable(CAP_SYS_ADMIN)) {
-                       pr_warn_once("%s (%d): Attempt to access syslog with "
-                                    "CAP_SYS_ADMIN but no CAP_SYSLOG "
-                                    "(deprecated).\n",
-                                current->comm, task_pid_nr(current));
-                       goto ok;
-               }
                return -EPERM;
        }
 ok: