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Subject: Re: [PATCH 5.14 018/334] nbd: add the check to prevent overflow in
 __nbd_ioctl()
To:     Nick Desaulniers <ndesaulniers@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
CC:     Arnd Bergmann <arnd@kernel.org>,
        Sedat Dilek <sedat.dilek@gmail.com>,
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        Nathan Chancellor <natechancellor@gmail.com>,
        open list <linux-kernel@vger.kernel.org>,
        linux-stable <stable@vger.kernel.org>,
        Hulk Robot <hulkci@huawei.com>,
        Josef Bacik <josef@toxicpanda.com>,
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        clang-built-linux <clang-built-linux@googlegroups.com>,
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        Kees Cook <keescook@chromium.org>
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From:   "libaokun (A)" <libaokun1@huawei.com>
Message-ID: <db321a38-f5f6-34cd-2f4f-37fc82201798@huawei.com>
Date:   Tue, 14 Sep 2021 10:13:23 +0800
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在 2021/9/14 7:23, Nick Desaulniers 写道:
> On Mon, Sep 13, 2021 at 4:00 PM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>> On Mon, Sep 13, 2021 at 2:15 PM Nick Desaulniers
>> <ndesaulniers@google.com> wrote:
>>> Sorry wrong diff:
>> Well, this second diff was seriously whitespace-damaged and hard to
>> read, but while it seems to be the same number of lines, it sure looks
>> a lot more readable in this format.
>>
>> Except I think that
>>
>>                  default: dividend / divisor);
>>
>> should really have parentheses around both of those macro arguments.
>>
>> That's a preexisting problem, but it should be fixed while at it.
> Ok, I'll send a revised v2 based on _Generic; Rasmus can help review
> when he's awake.
>
>> I'm also not sure why that (again, preexisting) BUILD_BUG_ON_MSG()
>> only checks the size of the dividend, not the divisor. Very strange.
>> But probably not worth worrying about.
> I sent a not-yet-applied diff of my not-yet-applied diff.  I was
> playing with this last week, and IIRC we had divisors that were less
> than 32b being promoted to int. But I'll test it some more.

How about deleting the check_mul_overflow in the __nbd_ioctl as follows?

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 5170a630778d..f404e0540476 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1393,7 +1393,6 @@ static int __nbd_ioctl(struct block_device *bdev, 
struct nbd_device *nbd,
                        unsigned int cmd, unsigned long arg)
  {
         struct nbd_config *config = nbd->config;
-       loff_t bytesize;

         switch (cmd) {
         case NBD_DISCONNECT:
@@ -1408,9 +1407,10 @@ static int __nbd_ioctl(struct block_device *bdev, 
struct nbd_device *nbd,
         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);
         case NBD_SET_TIMEOUT:
                 nbd_set_cmd_timeout(nbd, arg);
                 return 0;
--
2.31.1

-- 
With Best Regards,
Baokun Li