FAILED: patch "[PATCH] io_uring: Clean up a false-positive warning from GCC 9.3.0" failed to apply to 5.10-stable tree

FAILED: patch "[PATCH] io_uring: Clean up a false-positive warning from GCC 9.3.0" failed to apply to 5.10-stable tree

[gregkh]

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

Possible dependencies:

0d7c1153d929 ("io_uring: Clean up a false-positive warning from GCC 9.3.0")
d1fd1c201d75 ("io_uring: simplify selected buf handling")
3648e5265cfa ("io_uring: move up io_put_kbuf() and io_put_rw_kbuf()")
04c76b41ca97 ("io_uring: add option to skip CQE posting")
913a571affed ("io_uring: clean cqe filling functions")
7297ce3d5944 ("io_uring: improve send/recv error handling")
54daa9b2d80a ("io_uring: correct fill events helpers types")
867f8fa5aeb7 ("io_uring: inline io_req_needs_clean()")
d17e56eb4907 ("io_uring: remove struct io_completion")
d886e185a128 ("io_uring: control ->async_data with a REQ_F flag")
fff4e40e3094 ("io_uring: delay req queueing into compl-batch list")
51d48dab62ed ("io_uring: add more likely/unlikely() annotations")
7e3709d57651 ("io_uring: optimise kiocb layout")
30d51dd4ad20 ("io_uring: clean up buffer select")
a1cdbb4cb5f7 ("io_uring: comment why inline complete calls io_clean_op()")
ef05d9ebcc92 ("io_uring: kill off ->inflight_entry field")
6962980947e2 ("io_uring: restructure submit sqes to_submit checks")
d9f9d2842c91 ("io_uring: reshuffle queue_sqe completion handling")
f5ed3bcd5b11 ("io_uring: optimise batch completion")
b3fa03fd1b17 ("io_uring: convert iopoll_completed to store_release")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 0d7c1153d9291197c1dc473cfaade77acb874b4b Mon Sep 17 00:00:00 2001
From: Alviro Iskandar Setiawan <alviro.iskandar@gmail.com>
Date: Mon, 7 Feb 2022 21:05:33 +0700
Subject: [PATCH] io_uring: Clean up a false-positive warning from GCC 9.3.0

In io_recv(), if import_single_range() fails, the @flags variable is
uninitialized, then it will goto out_free.

After the goto, the compiler doesn't know that (ret < min_ret) is
always true, so it thinks the "if ((flags & MSG_WAITALL) ..."  path
could be taken.

The complaint comes from gcc-9 (Debian 9.3.0-22) 9.3.0:
```
  fs/io_uring.c:5238 io_recvfrom() error: uninitialized symbol 'flags'
```
Fix this by bypassing the @ret and @flags check when
import_single_range() fails.

Reasons:
 1. import_single_range() only returns -EFAULT when it fails.
 2. At that point, @flags is uninitialized and shouldn't be read.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Reported-by: "Chen, Rong A" <rong.a.chen@intel.com>
Link: https://lore.gnuweeb.org/timl/d33bb5a9-8173-f65b-f653-51fc0681c6d6@intel.com/
Cc: Pavel Begunkov <asml.silence@gmail.com>
Suggested-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Fixes: 7297ce3d59449de49d3c9e1f64ae25488750a1fc ("io_uring: improve send/recv error handling")
Signed-off-by: Alviro Iskandar Setiawan <alviro.iskandar@gmail.com>
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Link: https://lore.kernel.org/r/20220207140533.565411-1-ammarfaizi2@gnuweeb.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 2e04f718319d..3445c4da0153 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5228,7 +5228,6 @@ static int io_recv(struct io_kiocb *req, unsigned int issue_flags)
 		min_ret = iov_iter_count(&msg.msg_iter);
 
 	ret = sock_recvmsg(sock, &msg, flags);
-out_free:
 	if (ret < min_ret) {
 		if (ret == -EAGAIN && force_nonblock)
 			return -EAGAIN;
@@ -5236,9 +5235,9 @@ static int io_recv(struct io_kiocb *req, unsigned int issue_flags)
 			ret = -EINTR;
 		req_set_fail(req);
 	} else if ((flags & MSG_WAITALL) && (msg.msg_flags & (MSG_TRUNC | MSG_CTRUNC))) {
+out_free:
 		req_set_fail(req);
 	}
-
 	__io_req_complete(req, issue_flags, ret, io_put_kbuf(req));
 	return 0;
 }

Re: FAILED: patch "[PATCH] io_uring: Clean up a false-positive warning from GCC 9.3.0" failed to apply to 5.10-stable tree

[Alviro Iskandar Setiawan]

On Sun, Jan 22, 2023 at 9:44 PM <gregkh@linuxfoundation.org> wrote:
> The patch below does not apply to the 5.10-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.

That uninitialized reading is living in 5.10.y branch now
https://github.com/gregkh/linux/blob/v5.10.162/io_uring/io_uring.c#L4989-L5017

If this:

   ret = import_single_range(RE AD, buf, sr->len, &iov, &msg.msg_iter);

fails, this one (flags & MSG_WAITALL) may read an uninitialized
variable because @flags is uninitialized.

Fortunately, if import_single_range() fails, (ret < min_ret) is always
true, so this:

    ret < min_ret || ((flags & MSG_WAITALL)

will always short circuit. But no one tells the compiler if @ret is
always less than @min_ret in that case. So it can't prove that @flags
is never actually read. That still falls to undefined behavior anyway,
the compiler may emit "ud2" or similar trap for that or behave
randomly. IDK...

Re: FAILED: patch "[PATCH] io_uring: Clean up a false-positive warning from GCC 9.3.0" failed to apply to 5.10-stable tree

[Jens Axboe]

On 1/22/23 8:43 AM, Alviro Iskandar Setiawan wrote:
> On Sun, Jan 22, 2023 at 9:44 PM <gregkh@linuxfoundation.org> wrote:
>> The patch below does not apply to the 5.10-stable tree.
>> If someone wants it applied there, or to any other stable or longterm
>> tree, then please email the backport, including the original git commit
>> id to <stable@vger.kernel.org>.
> 
> That uninitialized reading is living in 5.10.y branch now
> https://github.com/gregkh/linux/blob/v5.10.162/io_uring/io_uring.c#L4989-L5017
> 
> If this:
> 
>    ret = import_single_range(RE AD, buf, sr->len, &iov, &msg.msg_iter);
> 
> fails, this one (flags & MSG_WAITALL) may read an uninitialized
> variable because @flags is uninitialized.
> 
> Fortunately, if import_single_range() fails, (ret < min_ret) is always
> true, so this:
> 
>     ret < min_ret || ((flags & MSG_WAITALL)
> 
> will always short circuit. But no one tells the compiler if @ret is
> always less than @min_ret in that case. So it can't prove that @flags
> is never actually read. That still falls to undefined behavior anyway,
> the compiler may emit "ud2" or similar trap for that or behave
> randomly. IDK...

Now handled for both trees.

-- 
Jens Axboe