[LTP] [PATCH v2 4/4] Add test for CVE 2020-29373

Petr Vorel
2021-02-08T09:48:15Z

Hi Martin,

> >> + /* Add spam requests to force async processing of the real test */
> >> + for (i = 0, tail = *uring.sqr_tail; i < 255; i++, tail++, sqe_ptr++) {
> >> + memset(sqe_ptr, 0, sizeof(*sqe_ptr));
> >> + sqe_ptr->opcode = IORING_OP_SENDMSG;
> >> + sqe_ptr->flags = IOSQE_IO_DRAIN;
> >> + sqe_ptr->fd = sockpair[0];
> >> + sqe_ptr->addr = (__u64)&spam_header;
> >> + sqe_ptr->user_data = SPAM_MARK;
> > Interesting, original reproducer uses here i

> >> + uring.sqr_array[tail & *uring.sqr_mask] = i;
> >> + }
> >> +
> >> + /* Add the real test to queue */
> >> + memset(sqe_ptr, 0, sizeof(*sqe_ptr));
> >> + sqe_ptr->opcode = IORING_OP_SENDMSG;
> >> + sqe_ptr->flags = IOSQE_IO_DRAIN;
> >> + sqe_ptr->fd = sendsock;
> >> + sqe_ptr->addr = (__u64)&beef_header;
> >> + sqe_ptr->user_data = BEEF_MARK;
> > and here also 255, you use much higher 0xbeef.

> > You probably have a good reason to use here 0xfa7 (higher value). But maybe
> > explaining why?

> The good reason is that I like puns. sqe_ptr->user_data is not processed
> by the kernel in any way except for copying the value into the
> completion queue when the I/O request finishes. And we don't care
> whether we can tell apart the spam request results from one another so
> giving them all the same marker is good enough.
Thanks for an explanation!

> >> + uring.sqr_array[tail & *uring.sqr_mask] = i;
> >> + count = ++i;
> >> + tail++;
> >> +
> >> + __atomic_store(uring.sqr_tail, &tail, __ATOMIC_RELEASE);
> >> + SAFE_IO_URING_ENTER(1, uring.fd, count, count, IORING_ENTER_GETEVENTS,
> >> + NULL);
> >> +
> >> + /* Check test results */
> >> + __atomic_load(uring.cqr_tail, &tail, __ATOMIC_ACQUIRE);
> >> +
> >> + for (i = *uring.cqr_head; i != tail; i++, count--) {
> >> + cqe_ptr = uring.cqr_entries + (i & *uring.cqr_mask);
> >> + TST_ERR = -cqe_ptr->res;
> >> +
> >> + if (cqe_ptr->user_data == SPAM_MARK) {
> >> + if (cqe_ptr->res >= 0 || cqe_ptr->res == -EAGAIN)
> >> + continue;
> >> +
> >> + tst_res(TFAIL | TTERRNO,
> >> + "Spam request failed unexpectedly");
> > I'm sorry, I'm lost to which TEST*() call this TTERRNO refers (there are mostly
> > SAFE_*() macros.

> I'm setting TST_ERR manually 6 lines above the tst_res() call. The errno
> value is in cqe_ptr->res.
Thank you, I'm blind :).

Anyway, merged. Thanks for your work!

BTW: test fails on my openSUSE kernel 5.11.0-rc6, which should have both kernel
fixes.

Kind regards,
Petr