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SubjectRe: [syzbot] KASAN: stack-out-of-bounds Read in iov_iter_revert
On Tue, 09 Nov 2021, Lee Jones wrote:

> On Mon, 08 Nov 2021, Jens Axboe wrote:
> > On 11/8/21 8:29 AM, Pavel Begunkov wrote:
> > > On 11/3/21 17:01, Lee Jones wrote:
> > >> Good afternoon Pavel,
> > >>
> > >>> syzbot has tested the proposed patch and the reproducer did not trigger any issue:
> > >>>
> > >>> Reported-and-tested-by: syzbot+9671693590ef5aad8953@syzkaller.appspotmail.com
> > >>>
> > >>> Tested on:
> > >>>
> > >>> commit: bff2c168 io_uring: don't retry with truncated iter
> > >>> git tree: https://github.com/isilence/linux.git truncate
> > >>> kernel config: https://syzkaller.appspot.com/x/.config?x=730106bfb5bf8ace
> > >>> dashboard link: https://syzkaller.appspot.com/bug?extid=9671693590ef5aad8953
> > >>> compiler: Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.1
> > >>>
> > >>> Note: testing is done by a robot and is best-effort only.
> > >>
> > >> As you can see in the 'dashboard link' above this bug also affects
> > >> android-5-10 which is currently based on v5.10.75.
> > >>
> > >> I see that the back-port of this patch failed in v5.10.y:
> > >>
> > >> https://lore.kernel.org/stable/163152589512611@kroah.com/
> > >>
> > >> And after solving the build-error by back-porting both:
> > >>
> > >> 2112ff5ce0c11 iov_iter: track truncated size
> > >> 89c2b3b749182 io_uring: reexpand under-reexpanded iters
> > >>
> > >> I now see execution tripping the WARN() in iov_iter_revert():
> > >>
> > >> if (WARN_ON(unroll > MAX_RW_COUNT))
> > >> return
> > >>
> > >> Am I missing any additional patches required to fix stable/v5.10.y?
> > >
> > > Is it the same syz test? There was a couple more patches for
> > > IORING_SETUP_IOPOLL, but strange if that's not the case.
> > >
> > >
> > > fwiw, Jens decided to replace it with another mechanism shortly
> > > after, so it may be a better idea to backport those. Jens,
> > > what do you think?
> > >
> > >
> > > commit 8fb0f47a9d7acf620d0fd97831b69da9bc5e22ed
> > > Author: Jens Axboe <axboe@kernel.dk>
> > > Date: Fri Sep 10 11:18:36 2021 -0600
> > >
> > > iov_iter: add helper to save iov_iter state
> > >
> > > commit cd65869512ab5668a5d16f789bc4da1319c435c4
> > > Author: Jens Axboe <axboe@kernel.dk>
> > > Date: Fri Sep 10 11:19:14 2021 -0600
> > >
> > > io_uring: use iov_iter state save/restore helpers
> >
> > Yes, I think backporting based on the save/restore setup is the
> > sanest way by far.
>
> Would you be kind enough to attempt to send these patches to Stable?
>
> When I tried to back-port them, the second one gave me trouble. And
> without the in depth knowledge of the driver/subsystem that you guys
> have, I found it almost impossible to resolve all of the conflicts:

Any movement on this chaps?

Not sure I am able to do this back-port without your help.

> diff --cc fs/io_uring.c
> index 104dff9c71314,25bda8a5a4e5d..0000000000000
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@@ -2567,57 -2603,20 +2568,64 @@@ static void io_complete_rw_common(struc
> }
>
> #ifdef CONFIG_BLOCK
> -static bool io_resubmit_prep(struct io_kiocb *req)
> +static bool io_resubmit_prep(struct io_kiocb *req, int error)
> {
> - struct io_async_rw *rw = req->async_data;
> + struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
> + ssize_t ret = -ECANCELED;
> + struct iov_iter iter;
> + int rw;
> +
> ++<<<<<<< HEAD
> + if (error) {
> + ret = error;
> + goto end_req;
> + }
> +
> + switch (req->opcode) {
> + case IORING_OP_READV:
> + case IORING_OP_READ_FIXED:
> + case IORING_OP_READ:
> + rw = READ;
> + break;
> + case IORING_OP_WRITEV:
> + case IORING_OP_WRITE_FIXED:
> + case IORING_OP_WRITE:
> + rw = WRITE;
> + break;
> + default:
> + printk_once(KERN_WARNING "io_uring: bad opcode in resubmit %d\n",
> + req->opcode);
> + goto end_req;
> + }
>
> + if (!req->async_data) {
> + ret = io_import_iovec(rw, req, &iovec, &iter, false);
> + if (ret < 0)
> + goto end_req;
> + ret = io_setup_async_rw(req, iovec, inline_vecs, &iter, false);
> + if (!ret)
> + return true;
> + kfree(iovec);
> + } else {
> + return true;
> + }
> +end_req:
> + req_set_fail_links(req);
> + return false;
> ++=======
> + if (!rw)
> + return !io_req_prep_async(req);
> + iov_iter_restore(&rw->iter, &rw->iter_state);
> + return true;
> ++>>>>>>> cd65869512ab5 (io_uring: use iov_iter state save/restore helpers)
> }
> +#endif
>
> -static bool io_rw_should_reissue(struct io_kiocb *req)
> +static bool io_rw_reissue(struct io_kiocb *req, long res)
> {
> +#ifdef CONFIG_BLOCK
> umode_t mode = file_inode(req->file)->i_mode;
> - struct io_ring_ctx *ctx = req->ctx;
> + int ret;
>
> if (!S_ISBLK(mode) && !S_ISREG(mode))
> return false;
> @@@ -3268,13 -3307,20 +3276,23 @@@ static int io_setup_async_rw(struct io_
> const struct iovec *fast_iov,
> struct iov_iter *iter, bool force)
> {
> - if (!force && !io_op_defs[req->opcode].needs_async_setup)
> + if (!force && !io_op_defs[req->opcode].needs_async_data)
> return 0;
> if (!req->async_data) {
> ++<<<<<<< HEAD
> + if (__io_alloc_async_data(req))
> ++=======
> + struct io_async_rw *iorw;
> +
> + if (io_alloc_async_data(req)) {
> + kfree(iovec);
> ++>>>>>>> cd65869512ab5 (io_uring: use iov_iter state save/restore helpers)
> return -ENOMEM;
> - }
>
> io_req_map_rw(req, iovec, fast_iov, iter);
> + iorw = req->async_data;
> + /* we've copied and mapped the iter, ensure state is saved */
> + iov_iter_save_state(&iorw->iter, &iorw->iter_state);
> }
> return 0;
> }
> @@@ -3417,18 -3443,28 +3436,43 @@@ static int io_read(struct io_kiocb *req
> struct kiocb *kiocb = &req->rw.kiocb;
> struct iov_iter __iter, *iter = &__iter;
> struct io_async_rw *rw = req->async_data;
> ++<<<<<<< HEAD
> + ssize_t io_size, ret, ret2;
> + bool no_async;
> ++=======
> + bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
> + struct iov_iter_state __state, *state;
> + ssize_t ret, ret2;
> ++>>>>>>> cd65869512ab5 (io_uring: use iov_iter state save/restore helpers)
>
> - if (rw) {
> + if (rw)
> iter = &rw->iter;
> ++<<<<<<< HEAD
> +
> + ret = io_import_iovec(READ, req, &iovec, iter, !force_nonblock);
> + if (ret < 0)
> + return ret;
> + io_size = iov_iter_count(iter);
> + req->result = io_size;
> + ret = 0;
> ++=======
> + state = &rw->iter_state;
> + /*
> + * We come here from an earlier attempt, restore our state to
> + * match in case it doesn't. It's cheap enough that we don't
> + * need to make this conditional.
> + */
> + iov_iter_restore(iter, state);
> + iovec = NULL;
> + } else {
> + ret = io_import_iovec(READ, req, &iovec, iter, !force_nonblock);
> + if (ret < 0)
> + return ret;
> + state = &__state;
> + iov_iter_save_state(iter, state);
> + }
> + req->result = iov_iter_count(iter);
> ++>>>>>>> cd65869512ab5 (io_uring: use iov_iter state save/restore helpers)
>
> /* Ensure we clear previously set non-block flag */
> if (!force_nonblock)
> @@@ -3436,15 -3472,17 +3480,23 @@@
> else
> kiocb->ki_flags |= IOCB_NOWAIT;
>
> +
> /* If the file doesn't support async, just async punt */
> - if (force_nonblock && !io_file_supports_nowait(req, READ)) {
> - ret = io_setup_async_rw(req, iovec, inline_vecs, iter, true);
> - return ret ?: -EAGAIN;
> - }
> + no_async = force_nonblock && !io_file_supports_async(req->file, READ);
> + if (no_async)
> + goto copy_iov;
>
> ++<<<<<<< HEAD
> + ret = rw_verify_area(READ, req->file, io_kiocb_ppos(kiocb), io_size);
> + if (unlikely(ret))
> + goto out_free;
> ++=======
> + ret = rw_verify_area(READ, req->file, io_kiocb_ppos(kiocb), req->result);
> + if (unlikely(ret)) {
> + kfree(iovec);
> + return ret;
> + }
> ++>>>>>>> cd65869512ab5 (io_uring: use iov_iter state save/restore helpers)
>
> ret = io_iter_do_read(req, iter);
>
> @@@ -3457,68 -3491,78 +3509,133 @@@
> /* IOPOLL retry should happen for io-wq threads */
> if (!force_nonblock && !(req->ctx->flags & IORING_SETUP_IOPOLL))
> goto done;
> - /* no retry on NONBLOCK nor RWF_NOWAIT */
> - if (req->flags & REQ_F_NOWAIT)
> + /* no retry on NONBLOCK marked file */
> + if (req->file->f_flags & O_NONBLOCK)
> goto done;
> ++<<<<<<< HEAD
> + /* some cases will consume bytes even on error returns */
> + iov_iter_revert(iter, io_size - iov_iter_count(iter));
> + ret = 0;
> + goto copy_iov;
> + } else if (ret < 0) {
> + /* make sure -ERESTARTSYS -> -EINTR is done */
> + goto done;
> + }
> +
> + /* read it all, or we did blocking attempt. no retry. */
> + if (!iov_iter_count(iter) || !force_nonblock ||
> + (req->file->f_flags & O_NONBLOCK) || !(req->flags & REQ_F_ISREG))
> + goto done;
> ++=======
> + ret = 0;
> + } else if (ret == -EIOCBQUEUED) {
> + goto out_free;
> + } else if (ret <= 0 || ret == req->result || !force_nonblock ||
> + (req->flags & REQ_F_NOWAIT) || !need_read_all(req)) {
> + /* read all, failed, already did sync or don't want to retry */
> + goto done;
> + }
> +
> + /*
> + * Don't depend on the iter state matching what was consumed, or being
> + * untouched in case of error. Restore it and we'll advance it
> + * manually if we need to.
> + */
> + iov_iter_restore(iter, state);
> +
> + ret2 = io_setup_async_rw(req, iovec, inline_vecs, iter, true);
> + if (ret2)
> + return ret2;
> ++>>>>>>> cd65869512ab5 (io_uring: use iov_iter state save/restore helpers)
>
> - iovec = NULL;
> + io_size -= ret;
> +copy_iov:
> + ret2 = io_setup_async_rw(req, iovec, inline_vecs, iter, true);
> + if (ret2) {
> + ret = ret2;
> + goto out_free;
> + }
> + if (no_async)
> + return -EAGAIN;
> rw = req->async_data;
> ++<<<<<<< HEAD
> + /* it's copied and will be cleaned with ->io */
> + iovec = NULL;
> + /* now use our persistent iterator, if we aren't already */
> + iter = &rw->iter;
> +retry:
> + rw->bytes_done += ret;
> + /* if we can retry, do so with the callbacks armed */
> + if (!io_rw_should_retry(req)) {
> + kiocb->ki_flags &= ~IOCB_WAITQ;
> + return -EAGAIN;
> + }
> +
> /*
> - * Now use our persistent iterator and state, if we aren't already.
> - * We've restored and mapped the iter to match.
> + * Now retry read with the IOCB_WAITQ parts set in the iocb. If we
> + * get -EIOCBQUEUED, then we'll get a notification when the desired
> + * page gets unlocked. We can also get a partial read here, and if we
> + * do, then just retry at the new offset.
> */
> - if (iter != &rw->iter) {
> - iter = &rw->iter;
> + ret = io_iter_do_read(req, iter);
> + if (ret == -EIOCBQUEUED) {
> + ret = 0;
> + goto out_free;
> + } else if (ret > 0 && ret < io_size) {
> + /* we got some bytes, but not all. retry. */
> + kiocb->ki_flags &= ~IOCB_WAITQ;
> + goto retry;
> + }
> ++=======
> ++ /*
> ++ * Now use our persistent iterator and state, if we aren't already.
> ++ * We've restored and mapped the iter to match.
> ++ */
> ++ if (iter != &rw->iter) {
> ++ iter = &rw->iter;
> + state = &rw->iter_state;
> + }
> +
> + do {
> + /*
> + * We end up here because of a partial read, either from
> + * above or inside this loop. Advance the iter by the bytes
> + * that were consumed.
> + */
> + iov_iter_advance(iter, ret);
> + if (!iov_iter_count(iter))
> + break;
> + rw->bytes_done += ret;
> + iov_iter_save_state(iter, state);
> +
> + /* if we can retry, do so with the callbacks armed */
> + if (!io_rw_should_retry(req)) {
> + kiocb->ki_flags &= ~IOCB_WAITQ;
> + return -EAGAIN;
> + }
> +
> + /*
> + * Now retry read with the IOCB_WAITQ parts set in the iocb. If
> + * we get -EIOCBQUEUED, then we'll get a notification when the
> + * desired page gets unlocked. We can also get a partial read
> + * here, and if we do, then just retry at the new offset.
> + */
> + ret = io_iter_do_read(req, iter);
> + if (ret == -EIOCBQUEUED)
> + return 0;
> + /* we got some bytes, but not all. retry. */
> + kiocb->ki_flags &= ~IOCB_WAITQ;
> + iov_iter_restore(iter, state);
> + } while (ret > 0);
> ++>>>>>>> cd65869512ab5 (io_uring: use iov_iter state save/restore helpers)
> done:
> - kiocb_done(kiocb, ret, issue_flags);
> + kiocb_done(kiocb, ret, cs);
> + ret = 0;
> out_free:
> - /* it's faster to check here then delegate to kfree */
> + /* it's reportedly faster than delegating the null check to kfree() */
> if (iovec)
> kfree(iovec);
> - return 0;
> + return ret;
> }
>
> static int io_write_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
> @@@ -3545,16 -3578,24 +3662,37 @@@ static int io_write(struct io_kiocb *re
> struct kiocb *kiocb = &req->rw.kiocb;
> struct iov_iter __iter, *iter = &__iter;
> struct io_async_rw *rw = req->async_data;
> ++<<<<<<< HEAD
> + ssize_t ret, ret2, io_size;
> ++=======
> + bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
> + struct iov_iter_state __state, *state;
> + ssize_t ret, ret2;
> ++>>>>>>> cd65869512ab5 (io_uring: use iov_iter state save/restore helpers)
>
> - if (rw) {
> + if (rw)
> iter = &rw->iter;
> ++<<<<<<< HEAD
> +
> + ret = io_import_iovec(WRITE, req, &iovec, iter, !force_nonblock);
> + if (ret < 0)
> + return ret;
> + io_size = iov_iter_count(iter);
> + req->result = io_size;
> ++=======
> + state = &rw->iter_state;
> + iov_iter_restore(iter, state);
> + iovec = NULL;
> + } else {
> + ret = io_import_iovec(WRITE, req, &iovec, iter, !force_nonblock);
> + if (ret < 0)
> + return ret;
> + state = &__state;
> + iov_iter_save_state(iter, state);
> + }
> + req->result = iov_iter_count(iter);
> + ret2 = 0;
> ++>>>>>>> cd65869512ab5 (io_uring: use iov_iter state save/restore helpers)
>
> /* Ensure we clear previously set non-block flag */
> if (!force_nonblock)
> @@@ -3610,14 -3656,14 +3748,20 @@@
> if ((req->ctx->flags & IORING_SETUP_IOPOLL) && ret2 == -EAGAIN)
> goto copy_iov;
> done:
> - kiocb_done(kiocb, ret2, issue_flags);
> + kiocb_done(kiocb, ret2, cs);
> } else {
> copy_iov:
> ++<<<<<<< HEAD
> + /* some cases will consume bytes even on error returns */
> + iov_iter_revert(iter, io_size - iov_iter_count(iter));
> ++=======
> + iov_iter_restore(iter, state);
> + if (ret2 > 0)
> + iov_iter_advance(iter, ret2);
> ++>>>>>>> cd65869512ab5 (io_uring: use iov_iter state save/restore helpers)
> ret = io_setup_async_rw(req, iovec, inline_vecs, iter, false);
> - return ret ?: -EAGAIN;
> + if (!ret)
> + return -EAGAIN;
> }
> out_free:
> /* it's reportedly faster than delegating the null check to kfree() */
>

--
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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