ext4: check if mount_opts is NUL-terminated in ext4_ioctl_set_tune_sb()

ext4: check if mount_opts is NUL-terminated in ext4_ioctl_set_tune_sb()

params.mount_opts may come as potentially non-NUL-term string.  Userspace
is expected to pass a NUL-term string.  Add an extra check to ensure this
holds true.  Note that further code utilizes strscpy_pad() so this is just
for proper informing the user of incorrect data being provided.

Found by Linux Verification Center (linuxtesting.org).

Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Reviewed-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Message-ID: <20251101160430.222297-2-pchelkin@ispras.ru>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org