Re: [PATCH 5.14 018/334] nbd: add the check to prevent overflow in __nbd_ioctl()

[libaokun (A)]

在 2021/9/14 7:23, Nick Desaulniers 写道:
> On Mon, Sep 13, 2021 at 4:00 PM Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> > On Mon, Sep 13, 2021 at 2:15 PM Nick Desaulniers
> > <ndesaulniers@xxxxxxxxxx> 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