Re: [syzbot] KASAN: stack-out-of-bounds Read in iov_iter_revert

[Lee Jones <lee.jones@linaro.org>]

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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