linux-kernel - [PATCH io_uring-5.17 v2] io_uring: Clean up a false-positive warning from GCC 9.3.0

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Message-Id: <20220207140533.565411-1-ammarfaizi2@gnuweeb.org>
Date:   Mon,  7 Feb 2022 21:05:33 +0700
From:   Ammar Faizi <ammarfaizi2@...weeb.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     GNU/Weeb Mailing List <gwml@...weeb.org>,
        io-uring Mailing list <io-uring@...r.kernel.org>,
        Tea Inside Mailing List <timl@...r.teainside.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alviro Iskandar Setiawan <alviro.iskandar@...il.com>,
        kernel test robot <lkp@...el.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        "Chen, Rong A" <rong.a.chen@...el.com>,
        Pavel Begunkov <asml.silence@...il.com>,
        Ammar Faizi <ammarfaizi2@...weeb.org>
Subject: [PATCH io_uring-5.17 v2] io_uring: Clean up a false-positive warning from GCC 9.3.0

From: Alviro Iskandar Setiawan <alviro.iskandar@...il.com>

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@...el.com>
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Reported-by: "Chen, Rong A" <rong.a.chen@...el.com>
Link: https://lore.gnuweeb.org/timl/d33bb5a9-8173-f65b-f653-51fc0681c6d6@intel.com/
Cc: Pavel Begunkov <asml.silence@...il.com>
Suggested-by: Ammar Faizi <ammarfaizi2@...weeb.org>
Fixes: 7297ce3d59449de49d3c9e1f64ae25488750a1fc ("io_uring: improve send/recv error handling")
Signed-off-by: Alviro Iskandar Setiawan <alviro.iskandar@...il.com>
Signed-off-by: Ammar Faizi <ammarfaizi2@...weeb.org>
---

 v2:
   - Update the subject line

 fs/io_uring.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

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;
 }

base-commit: f6133fbd373811066c8441737e65f384c8f31974
-- 
2.32.0