cap_syslog: accept CAP_SYS_ADMIN for now

In commit ce6ada35bdf7 ("security: Define CAP_SYSLOG") Serge Hallyn
introduced CAP_SYSLOG, but broke backwards compatibility by no longer
accepting CAP_SYS_ADMIN as an override (it would cause a warning and
then reject the operation).

Re-instate CAP_SYS_ADMIN - but keeping the warning - as an acceptable
capability until any legacy applications have been updated.  There are
apparently applications out there that drop all capabilities except for
CAP_SYS_ADMIN in order to access the syslog.

(This is a re-implementation of a patch by Serge, cleaning the logic up
and making the code more readable)

Acked-by: Serge Hallyn <serge@hallyn.com>
Reviewed-by: James Morris <jmorris@namei.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/printk.c b/kernel/printk.c
index 2ddbdc7..3623152 100644 (file)
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -262,25 +262,47 @@ int dmesg_restrict = 1;
 int dmesg_restrict;
 #endif
 
+static int syslog_action_restricted(int type)
+{
+       if (dmesg_restrict)
+               return 1;
+       /* Unless restricted, we allow "read all" and "get buffer size" for everybody */
+       return type != SYSLOG_ACTION_READ_ALL && type != SYSLOG_ACTION_SIZE_BUFFER;
+}
+
+static int check_syslog_permissions(int type, bool from_file)
+{
+       /*
+        * If this is from /proc/kmsg and we've already opened it, then we've
+        * already done the capabilities checks at open time.
+        */
+       if (from_file && type != SYSLOG_ACTION_OPEN)
+               return 0;
+
+       if (syslog_action_restricted(type)) {
+               if (capable(CAP_SYSLOG))
+                       return 0;
+               /* For historical reasons, accept CAP_SYS_ADMIN too, with a warning */
+               if (capable(CAP_SYS_ADMIN)) {
+                       WARN_ONCE(1, "Attempt to access syslog with CAP_SYS_ADMIN "
+                                "but no CAP_SYSLOG (deprecated).\n");
+                       return 0;
+               }
+               return -EPERM;
+       }
+       return 0;
+}
+
 int do_syslog(int type, char __user *buf, int len, bool from_file)
 {
        unsigned i, j, limit, count;
        int do_clear = 0;
        char c;
-       int error = 0;
+       int error;
 
-       /*
-        * If this is from /proc/kmsg we only do the capabilities checks
-        * at open time.
-        */
-       if (type == SYSLOG_ACTION_OPEN || !from_file) {
-               if (dmesg_restrict && !capable(CAP_SYSLOG))
-                       goto warn; /* switch to return -EPERM after 2.6.39 */
-               if ((type != SYSLOG_ACTION_READ_ALL &&
-                    type != SYSLOG_ACTION_SIZE_BUFFER) &&
-                   !capable(CAP_SYSLOG))
-                       goto warn; /* switch to return -EPERM after 2.6.39 */
-       }
+       error = check_syslog_permissions(type, from_file);
+       if (error)
+               goto out;
 
        error = security_syslog(type);
        if (error)
@@ -423,12 +445,6 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
        }
 out:
        return error;
-warn:
-       /* remove after 2.6.39 */
-       if (capable(CAP_SYS_ADMIN))
-               WARN_ONCE(1, "Attempt to access syslog with CAP_SYS_ADMIN "
-                 "but no CAP_SYSLOG (deprecated and denied).\n");
-       return -EPERM;
 }
 
 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)