kprobes: handle empty/invalid input to debugfs "enabled" file

When writing invalid input to 'debug/kprobes/enabled' it'll silently be
ignored.  Even worse, when writing an empty string to this file, the
outcome is purely random as the switch statement will make its decision
based on the value of an uninitialized stack variable.

Fix this by handling invalid/empty input as error returning -EINVAL.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index bddf3b201a48..6e33498d665c 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -2332,6 +2332,7 @@ static ssize_t write_enabled_file_bool(struct file *file,
         if (copy_from_user(buf, user_buf, buf_size))
                 return -EFAULT;
 
+        buf[buf_size] = '\0';
         switch (buf[0]) {
         case 'y':
         case 'Y':
@@ -2343,6 +2344,8 @@ static ssize_t write_enabled_file_bool(struct file *file,
         case '0':
                 disarm_all_kprobes();
                 break;
+        default:
+                return -EINVAL;
         }
 
         return count;