proc: proc_skip_spaces() shouldn't think it is working on C strings

stable inclusion
from stable-v5.10.157
commit 9ba389863ac63032d4b6ffad2c90a62cd78082ee
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I65TQE
CVE: CVE-2022-4378

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9ba389863ac63032d4b6ffad2c90a62cd78082ee



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

commit bce93322 upstream.

proc_skip_spaces() seems to think it is working on C strings, and ends
up being just a wrapper around skip_spaces() with a really odd calling
convention.

Instead of basing it on skip_spaces(), it should have looked more like
proc_skip_char(), which really is the exact same function (except it
skips a particular character, rather than whitespace).  So use that as
inspiration, odd coding and all.

Now the calling convention actually makes sense and works for the
intended purpose.

Reported-and-tested-by: Kyle Zeng <zengyhkyle@gmail.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Long Li <leo.lilong@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>