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

[Mathias Krause]

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.

Cc: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxx>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@xxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Mathias Krause <minipli@xxxxxxxxxxxxxx>
---
 kernel/kprobes.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 3fed7f0..948b597 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -2322,6 +2322,7 @@ 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':
@@ -2333,6 +2334,8 @@ static ssize_t write_enabled_file_bool(struct file *file,
 	case '0':
 		disarm_all_kprobes();
 		break;
+	default:
+		return -EINVAL;
 	}
 
 	return count;
-- 
1.7.10.4

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