security_syslog() should be called once only

The final version of commit 637241a900cb ("kmsg: honor dmesg_restrict
sysctl on /dev/kmsg") lost few hooks, as result security_syslog() are
processed incorrectly:

- open of /dev/kmsg checks syslog access permissions by using
  check_syslog_permissions() where security_syslog() is not called if
  dmesg_restrict is set.

- syslog syscall and /proc/kmsg calls do_syslog() where security_syslog
  can be executed twice (inside check_syslog_permissions() and then
  directly in do_syslog())

With this patch security_syslog() is called once only in all
syslog-related operations regardless of dmesg_restrict value.

Fixes: 637241a900cb ("kmsg: honor dmesg_restrict sysctl on /dev/kmsg")
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Josh Boyer <jwboyer@redhat.com>
Cc: Eric Paris <eparis@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 7 deletions

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ae980dc3ac1e..45fa8c88ac47 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -496,11 +496,11 @@ int check_syslog_permissions(int type, bool from_file)
          * already done the capabilities checks at open time.
          */
         if (from_file && type != SYSLOG_ACTION_OPEN)
-                return 0;
+                goto ok;
 
         if (syslog_action_restricted(type)) {
                 if (capable(CAP_SYSLOG))
-                        return 0;
+                        goto ok;
                 /*
                  * For historical reasons, accept CAP_SYS_ADMIN too, with
                  * a warning.
@@ -510,10 +510,11 @@ int check_syslog_permissions(int type, bool from_file)
                                      "CAP_SYS_ADMIN but no CAP_SYSLOG "
                                      "(deprecated).\n",
                                  current->comm, task_pid_nr(current));
-                        return 0;
+                        goto ok;
                 }
                 return -EPERM;
         }
+ok:
         return security_syslog(type);
 }
 
@@ -1299,10 +1300,6 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
         if (error)
                 goto out;
 
-        error = security_syslog(type);
-        if (error)
-                return error;
-
         switch (type) {
         case SYSLOG_ACTION_CLOSE:       /* Close log */
                 break;