From c366a7b5ed7564e41345c380285bd3f6cb98971b Mon Sep 17 00:00:00 2001 From: Pengpeng Hou Date: Fri, 17 Apr 2026 15:35:30 +0800 Subject: 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 Reviewed-by: Benjamin Block Reviewed-by: Vasily Gorbik Tested-by: Vasily Gorbik Link: https://lore.kernel.org/r/20260417073530.96002-1-pengpeng@iscas.ac.cn Signed-off-by: Vasily Gorbik Signed-off-by: Alexander Gordeev --- arch/s390/kernel/debug.c | 3 +++ 1 file changed, 3 insertions(+) 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; -- cgit v1.2.3