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Date: Mon, 9 Mar 2026 15:54:21 -0600
From: Keith Busch <kbusch@kernel.org>
To: Caleb Sander Mateos <csander@purestorage.com>
Cc: Tom Ryan <ryan36005@gmail.com>, io-uring@vger.kernel.org,
	Jens Axboe <axboe@kernel.dk>, Greg KH <gregkh@linuxfoundation.org>
Subject: Re: io_uring: OOB read in SQE_MIXED mode via sq_array physical index
 bypass
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On Mon, Mar 09, 2026 at 02:45:59PM -0700, Caleb Sander Mateos wrote:
> On Mon, Mar 9, 2026 at 2:34 PM Keith Busch <kbusch@kernel.org> wrote:
> >
> > On Mon, Mar 09, 2026 at 02:20:38PM -0700, Tom Ryan wrote:
> > > Patch attached.
> >
> > You can just submit the patch as text in the mail message.
> >
> > > @@ -1747,6 +1747,9 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req,
> > >               if (!(ctx->flags & IORING_SETUP_SQE_MIXED) || *left < 2 ||
> > >                   !(ctx->cached_sq_head & (ctx->sq_entries - 1)))
> > >                       return io_init_fail_req(req, -EINVAL);
> > > +             /* Validate physical SQE index has room for 128-byte read */
> > > +             if ((unsigned)(sqe - ctx->sq_sqes) >= ctx->sq_entries - 1)
> > > +                     return io_init_fail_req(req, -EINVAL);
> >
> > Isn't this new check redundant with the "left < 2" check preceding it?
> 
> I think it's orthogonal with *left < 2. How many SQEs are remaining to
> submit is unrelated to the index of each SQE. It is, however,
> redundant with !(ctx->cached_sq_head & (ctx->sq_entries - 1)), but
> only in the IORING_SETUP_NO_SQARRAY case. For
> non-IORING_SETUP_NO_SQARRAY rings, the SQ indirection array entry can
> point to the last entry of the SQE array, causing the big SQE to
> extend past the end. Probably, this added condition can replace
> !(ctx->cached_sq_head & (ctx->sq_entries - 1)). That checks whether
> this is the last entry *in the SQ indirection array*, but it should be
> checking the SQE array.

Oh, right. The left < 2 was to confirm we have contiguous entries for a
big sqe, but you could index to an unaligned end with the sqarray.

Folding this into the previous 'if' sounds good. And please consider an
addition to liburing tests.