cifs: sanitize multiple delimiters in prepath

mainline inclusion
from mainline-v5.16-rc6
commit a3108089
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6D6RL
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a31080899d5fdafcccf7f39dd214a814a2c82626

--------------------------------

mount.cifs can pass a device with multiple delimiters in it. This will
cause rename(2) to fail with ENOENT.

V2:
  - Make sanitize_path more readable.
  - Fix multiple delimiters between UNC and prepath.
  - Avoid a memory leak if a bad user starts putting a lot of delimiters
    in the path on purpose.

BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=2031200


Fixes: 24e0a1ef ("cifs: switch to new mount api")
Cc: stable@vger.kernel.org # 5.11+
Acked-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Thiago Rafael Becker <trbecker@gmail.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

conflicts:
	fs/cifs/fs_context.c

Signed-off-by: ZhaoLong Wang <wangzhaolong1@huawei.com>
Reviewed-by: Zhang Xiaoxu <zhangxiaoxu5@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>