linux-kernel - RE: [PATCH 5.14 018/334] nbd: add the check to prevent overflow in __nbd

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Date:   Tue, 14 Sep 2021 08:14:10 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'libaokun (A)'" <libaokun1@...wei.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
CC:     Arnd Bergmann <arnd@...nel.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        open list <linux-kernel@...r.kernel.org>,
        linux-stable <stable@...r.kernel.org>,
        Hulk Robot <hulkci@...wei.com>,
        Josef Bacik <josef@...icpanda.com>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        "lkft-triage@...ts.linaro.org" <lkft-triage@...ts.linaro.org>,
        "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
        Kees Cook <keescook@...omium.org>
Subject: RE: [PATCH 5.14 018/334] nbd: add the check to prevent overflow in
 __nbd_ioctl()

...
>          case NBD_SET_SIZE:
>                  return nbd_set_size(nbd, arg, config->blksize);
>          case NBD_SET_SIZE_BLOCKS:
> -               if (check_mul_overflow((loff_t)arg, config->blksize,
> &bytesize))
> +               if (arg && (LLONG_MAX / arg <= config->blksize))
>                          return -EINVAL;
> -               return nbd_set_size(nbd, bytesize, config->blksize);
> +               return nbd_set_size(nbd, arg * config->blksize,
> +                                   config->blksize);

Shouldn't there just be sanity bound checks on 'config->blksize' and
'arg' so that the product is never going to overflow?

It isn't as though any values near the overflow limit are sane.

I suspect you could check config->blksize <= 64k && arg <= 32k
and even that would be generous.

	David

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