FAILED: patch "[PATCH] s390/debug: Reject zero-length input before trimming a" failed to apply to 6.6-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x c366a7b5ed7564e41345c380285bd3f6cb98971b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026051255-pulverize-ducking-c2ed@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From c366a7b5ed7564e41345c380285bd3f6cb98971b Mon Sep 17 00:00:00 2001
From: Pengpeng Hou <pengpeng@iscas.ac.cn>
Date: Fri, 17 Apr 2026 15:35:30 +0800
Subject: [PATCH] s390/debug: Reject zero-length input before trimming a
 newline

debug_get_user_string() duplicates the userspace buffer with
memdup_user_nul() and then unconditionally looks at buffer[user_len - 1]
to strip a trailing newline.

A zero-length write reaches this helper unchanged, so the newline trim
reads before the start of the allocated buffer.

Reject empty writes before accessing the last input byte.

Fixes: 66a464dbc8e0 ("[PATCH] s390: debug feature changes")
Cc: stable@vger.kernel.org
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Tested-by: Vasily Gorbik <gor@linux.ibm.com>
Link: https://lore.kernel.org/r/20260417073530.96002-1-pengpeng@iscas.ac.cn
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

diff --git a/arch/s390/kernel/debug.c b/arch/s390/kernel/debug.c
index 31430e9bcfdd..2612f634e826 100644
--- a/arch/s390/kernel/debug.c
+++ b/arch/s390/kernel/debug.c
@@ -1414,6 +1414,9 @@ static inline char *debug_get_user_string(const char __user *user_buf,
 {
 	char *buffer;
 
+	if (!user_len)
+		return ERR_PTR(-EINVAL);
+
 	buffer = memdup_user_nul(user_buf, user_len);
 	if (IS_ERR(buffer))
 		return buffer;