linux-kernel - [PATCH] Kernel: Improvement in code readability when memdup_user

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Date:   Fri, 11 Nov 2016 14:37:15 +0530
From:   Sachin Shukla <sachin.s5@...sung.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Serge Hallyn <serge@...lyn.com>,
        Andrey Vagin <avagin@...nvz.org>, linux-kernel@...r.kernel.org,
        sachiniiitm@...il.com
Cc:     ravikant.s2@...sung.com, p.shailesh@...sung.com,
        ashish.kalra@...sung.com, vidushi.koul@...sung.com
Subject: [PATCH] Kernel: Improvement in code readability when memdup_user_nul()
 fails.

From: "Sachin Shukla" <sachin.s5@...sung.com>

There is no need to call kfree() if memdup_user_nul() fails, as no memory
was allocated and the error in the error-valued pointer should be returned.

Signed-off-by: Sachin Shukla <sachin.s5@...sung.com>
---
 kernel/user_namespace.c |   25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 86b7854..a0ffbf0 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -672,28 +672,31 @@ static ssize_t map_write(struct file *file, const char __user *buf,
 	 */
 	mutex_lock(&userns_state_mutex);
 
-	ret = -EPERM;
 	/* Only allow one successful write to the map */
-	if (map->nr_extents != 0)
-		goto out;
+	if (map->nr_extents != 0) {
+		mutex_unlock(&userns_state_mutex);
+		return -EPERM;
+	}
 
 	/*
 	 * Adjusting namespace settings requires capabilities on the target.
 	 */
-	if (cap_valid(cap_setid) && !file_ns_capable(file, ns, CAP_SYS_ADMIN))
-		goto out;
+	if (cap_valid(cap_setid) && !file_ns_capable(file, ns, CAP_SYS_ADMIN)) {
+		mutex_unlock(&userns_state_mutex);
+		return -EPERM;
+	}
 
 	/* Only allow < page size writes at the beginning of the file */
-	ret = -EINVAL;
-	if ((*ppos != 0) || (count >= PAGE_SIZE))
-		goto out;
+	if ((*ppos != 0) || (count >= PAGE_SIZE)) {
+		mutex_unlock(&userns_state_mutex);
+		return -EINVAL;
+	}
 
 	/* Slurp in the user data */
 	kbuf = memdup_user_nul(buf, count);
 	if (IS_ERR(kbuf)) {
-		ret = PTR_ERR(kbuf);
-		kbuf = NULL;
-		goto out;
+		mutex_unlock(&userns_state_mutex);
+		return PTR_ERR(kbuf);
 	}
 
 	/* Parse the user data */
-- 
1.7.9.5