check_syslog_permissions() cleanup

Patch fixes drawbacks in heck_syslog_permissions() noticed by AKPM:
"from_file handling makes me cry.

That's not a boolean - it's an enumerated value with two values
currently defined.

But the code in check_syslog_permissions() treats it as a boolean and
also hardwires the knowledge that SYSLOG_FROM_PROC == 1 (or == `true`).

And the name is wrong: it should be called from_proc to match
SYSLOG_FROM_PROC."
Signed-off-by: NVasily 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: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/linux/syslog.h

@@ -47,12 +47,12 @@
 #define SYSLOG_FROM_READER           0
 #define SYSLOG_FROM_PROC             1
 
-int do_syslog(int type, char __user *buf, int count, bool from_file);
+int do_syslog(int type, char __user *buf, int count, int source);
 
 #ifdef CONFIG_PRINTK
-int check_syslog_permissions(int type, bool from_file);
+int check_syslog_permissions(int type, int source);
 #else
-static inline int check_syslog_permissions(int type, bool from_file)
+static inline int check_syslog_permissions(int type, int source)
 {
 	return 0;
 }

kernel/printk/printk.c

@@ -489,13 +489,13 @@ static int syslog_action_restricted(int type)
 	       type != SYSLOG_ACTION_SIZE_BUFFER;
 }
 
-int check_syslog_permissions(int type, bool from_file)
+int check_syslog_permissions(int type, int source)
 {
 	/*
 	 * 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)
+	if (source == SYSLOG_FROM_PROC && type != SYSLOG_ACTION_OPEN)
 		goto ok;
 
 	if (syslog_action_restricted(type)) {
@@ -1290,13 +1290,13 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	return len;
 }
 
-int do_syslog(int type, char __user *buf, int len, bool from_file)
+int do_syslog(int type, char __user *buf, int len, int source)
 {
 	bool clear = false;
 	static int saved_console_loglevel = LOGLEVEL_DEFAULT;
 	int error;
 
-	error = check_syslog_permissions(type, from_file);
+	error = check_syslog_permissions(type, source);
 	if (error)
 		goto out;
 
@@ -1379,7 +1379,7 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
 			syslog_prev = 0;
 			syslog_partial = 0;
 		}
-		if (from_file) {
+		if (source == SYSLOG_FROM_PROC) {
 			/*
 			 * Short-cut for poll(/"proc/kmsg") which simply checks
 			 * for pending data, not the size; return the count of