[ Upstream commit c366a7b5ed ]
debug_get_user_string() copies the userspace buffer into a newly
allocated NUL-terminated buffer 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: 66a464dbc8 ("[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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
1d6ceb529a