linux-kernel - [PATCH] s390/debug: Replace kmalloc() + copy_from_user() with memdup_user

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Message-ID: <20250904114031.353365-2-thorsten.blum@linux.dev>
Date: Thu,  4 Sep 2025 13:40:29 +0200
From: Thorsten Blum <thorsten.blum@...ux.dev>
To: Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	Halil Pasic <pasic@...ux.ibm.com>,
	Niklas Schnelle <schnelle@...ux.ibm.com>,
	"Bill O'Donnell" <bodonnel@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Tigran Mkrtchyan <tigran.mkrtchyan@...y.de>,
	Joel Granados <joel.granados@...nel.org>
Cc: Thorsten Blum <thorsten.blum@...ux.dev>,
	Wei Liu <wei.liu@...nel.org>,
	linux-s390@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] s390/debug: Replace kmalloc() + copy_from_user() with memdup_user_nul()

Replace kmalloc() followed by copy_from_user() with memdup_user_nul() to
improve and simplify debug_get_user_string(). Remove the manual
NUL-termination.

No functional changes intended.

Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>
---
 arch/s390/kernel/debug.c | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/arch/s390/kernel/debug.c b/arch/s390/kernel/debug.c
index c62100dc62c8..6a26f202441d 100644
--- a/arch/s390/kernel/debug.c
+++ b/arch/s390/kernel/debug.c
@@ -1416,18 +1416,12 @@ static inline char *debug_get_user_string(const char __user *user_buf,
 {
 	char *buffer;
 
-	buffer = kmalloc(user_len + 1, GFP_KERNEL);
-	if (!buffer)
-		return ERR_PTR(-ENOMEM);
-	if (copy_from_user(buffer, user_buf, user_len) != 0) {
-		kfree(buffer);
-		return ERR_PTR(-EFAULT);
-	}
+	buffer = memdup_user_nul(user_buf, user_len);
+	if (IS_ERR(buffer))
+		return buffer;
 	/* got the string, now strip linefeed. */
 	if (buffer[user_len - 1] == '\n')
 		buffer[user_len - 1] = 0;
-	else
-		buffer[user_len] = 0;
 	return buffer;
 }
 
-- 
2.51.0