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From:   Punit Agrawal <punitagrawal@gmail.com>
To:     mhiramat@kernel.org, naveen.n.rao@linux.ibm.com,
        anil.s.keshavamurthy@intel.com, davem@davemloft.net
Cc:     Punit Agrawal <punitagrawal@gmail.com>,
        linux-kernel@vger.kernel.org, guoren@kernel.org,
        linux-csky@vger.kernel.org
Subject: [PATCH 1/5] kprobes: Do not use local variable when creating debugfs file
Date:   Wed,  9 Jun 2021 19:50:15 +0900
Message-Id: <20210609105019.3626677-2-punitagrawal@gmail.com>
In-Reply-To: <20210609105019.3626677-1-punitagrawal@gmail.com>
References: <20210609105019.3626677-1-punitagrawal@gmail.com>
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debugfs_create_file() takes a pointer argument that can be used during
file operation callbacks (accessible via i_private in the inode
structure). An obvious requirement is for the pointer to refer to
valid memory when used.

When creating the debugfs file to dynamically enable / disable
kprobes, a pointer to local variable is passed to
debugfs_create_file(); which will go out of scope when the init
function returns. The reason this hasn't triggered random memory
corruption is because the pointer is not accessed during the debugfs
file callbacks.

Fix the incorrect (and unnecessary) usage of local variable during
debugfs_file_create() by passing NULL instead.

Signed-off-by: Punit Agrawal <punitagrawal@gmail.com>
---
 kernel/kprobes.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 745f08fdd7a6..fdb1ea2e963b 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -2816,13 +2816,12 @@ static const struct file_operations fops_kp = {
 static int __init debugfs_kprobe_init(void)
 {
 	struct dentry *dir;
-	unsigned int value = 1;
 
 	dir = debugfs_create_dir("kprobes", NULL);
 
 	debugfs_create_file("list", 0400, dir, NULL, &kprobes_fops);
 
-	debugfs_create_file("enabled", 0600, dir, &value, &fops_kp);
+	debugfs_create_file("enabled", 0600, dir, NULL, &fops_kp);
 
 	debugfs_create_file("blacklist", 0400, dir, NULL,
 			    &kprobe_blacklist_fops);
-- 
2.30.2