On Wed, Oct 30, 2024 at 07:22:49AM -0600, Jens Axboe wrote:
> On 10/30/24 5:40 AM, Dan Carpenter wrote:
> > Hello Jens Axboe,
> >
> > Commit 4b926ab18279 ("io_uring: add support for fixed wait regions")
> > from Oct 22, 2024 (linux-next), leads to the following Smatch static
> > checker warning:
> >
> > io_uring/register.c:616 io_register_cqwait_reg()
> > warn: was expecting a 64 bit value instead of '~(~(((1) << 12) - 1))'
> >
> > io_uring/register.c
> > 594 static int io_register_cqwait_reg(struct io_ring_ctx *ctx, void __user *uarg)
> > 595 {
> > 596 struct io_uring_cqwait_reg_arg arg;
> > 597 struct io_uring_reg_wait *reg;
> > 598 struct page **pages;
> > 599 unsigned long len;
> > 600 int nr_pages, poff;
> > 601 int ret;
> > 602
> > 603 if (ctx->cq_wait_page || ctx->cq_wait_arg)
> > 604 return -EBUSY;
> > 605 if (copy_from_user(&arg, uarg, sizeof(arg)))
> > 606 return -EFAULT;
> > 607 if (!arg.nr_entries || arg.flags)
> > 608 return -EINVAL;
> > 609 if (arg.struct_size != sizeof(*reg))
> > 610 return -EINVAL;
> > 611 if (check_mul_overflow(arg.struct_size, arg.nr_entries, &len))
> > 612 return -EOVERFLOW;
> > 613 if (len > PAGE_SIZE)
> > 614 return -EINVAL;
> > 615 /* offset + len must fit within a page, and must be reg_wait aligned */
> > --> 616 poff = arg.user_addr & ~PAGE_MASK;
> >
> > This is a harmless thing, but on 32 bit systems you can put whatever you want in
> > the high 32 bits of arg.user_addr and it won't affect anything.
>
> That is certainly true, it'll get masked away. I suspect this kind of
> thing is everywhere, though? What do you suggest?
The way that I normally see these warnings is with code like
"if (u64flags & ~mask)" where only the first 3 bits of u64flags are used. It's
not normally a real life bug. Normally fix them the warning, but I have 174 old
warnings from before I started complaining about them.
Maybe:
if (U32_MAX >= SIZE_MAX && arg.user_addr > SIZE_MAX)
return -EINVAL;
This code works fine as-is, but eventually I want this code to trigger a couple
more static checker warnings. It's so suspicious because we're truncating user
data then re-using the same untruncated variable again.
regards,
dan carpenter
