syslog: check cap_syslog when dmesg_restrict

Eric Paris pointed out that it doesn't make sense to require
both CAP_SYS_ADMIN and CAP_SYSLOG for certain syslog actions.
So require CAP_SYSLOG, not CAP_SYS_ADMIN, when dmesg_restrict
is set.

(I'm also consolidating the now common error path)

Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Acked-by: Eric Paris <eparis@redhat.com>
Acked-by: Kees Cook <kees.cook@canonical.com>
Signed-off-by: James Morris <jmorris@namei.org>

diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 209e1584c3dc25e8e1af61a3061c779a28f5d11e..574067194f3870cd4c36d915afb8ae04f9004b96 100644 (file)
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -219,7 +219,7 @@ dmesg_restrict:
 This toggle indicates whether unprivileged users are prevented from using
 dmesg(8) to view messages from the kernel's log buffer.  When
 dmesg_restrict is set to (0) there are no restrictions.  When
-dmesg_restrict is set set to (1), users must have CAP_SYS_ADMIN to use
+dmesg_restrict is set set to (1), users must have CAP_SYSLOG to use
 dmesg(8).
 
 The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the default

diff --git a/kernel/printk.c b/kernel/printk.c
index 0712380737b39dc42045ec612685fb4f43f0684f..0cecba0596663c08b7ce201e1c78d30fef72bebd 100644 (file)
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -279,18 +279,12 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
         * at open time.
         */
        if (type == SYSLOG_ACTION_OPEN || !from_file) {
-               if (dmesg_restrict && !capable(CAP_SYS_ADMIN))
-                       return -EPERM;
+               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)) {
-                       /* remove after 2.6.38 */
-                       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;
-               }
+                   !capable(CAP_SYSLOG))
+                       goto warn; /* switch to return -EPERM after 2.6.39 */
        }
 
        error = security_syslog(type);
@@ -434,6 +428,12 @@ 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)