Re: [PATCH v3] iov_iter: Use iov_offset for length calculation in iov_iter_aligned_bvec

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 28 Apr 2025 15:28:48 +0530 Nitesh Shetty <nj.shetty@samsung.com> wrote:

> If iov_offset is non-zero, then we need to consider iov_offset in length
> calculation, otherwise we might pass smaller IOs such as 512 bytes, in
> below scenario[1].
> This issue is reproducible using lib-uring test/fixed-seg.c application
> with fixed buffer on a 512 LBA formatted device.
> 
> [1]
> At present we pass the alignment check,
> for 512 LBA formatted devices, len_mask = 511
> when IO is smaller, i->count = 512
> has an offset, i->io_offset = 3584
> with bvec values, bvec->bv_offset = 256, bvec->bv_len = 3840.
> In short, the first 256 bytes are in the current page,
> next 256 bytes are in the another page.
> Ideally we expect to fail the IO.

Thanks.  Can you please send us a description of the userspace-visible
effects of this issue?  That will help others to determine whether a
-stable backport is desirable and it will be helpful to people who are
wondering whether this patch will fix an issue they are experiencing.