proc: avoid integer type confusion in get_proc_long

stable inclusion
from stable-v5.10.157
commit 4aa32aaef6c1b5e39ae2508ec596bd7b67871043
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=4aa32aaef6c1b5e39ae2508ec596bd7b67871043



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

commit e6cfaf34 upstream.

proc_get_long() is passed a size_t, but then assigns it to an 'int'
variable for the length.  Let's not do that, even if our IO paths are
limited to MAX_RW_COUNT (exactly because of these kinds of type errors).

So do the proper test in the rigth type.

Reported-by: Kyle Zeng <zengyhkyle@gmail.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>