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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
        Jakub Kicinski <kuba@kernel.org>
Subject: [PATCH 5.9 11/46] tun: honor IOCB_NOWAIT flag
Date:   Sun,  6 Dec 2020 12:17:19 +0100
Message-Id: <20201206111557.005207131@linuxfoundation.org>
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References: <20201206111556.455533723@linuxfoundation.org>
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From: Jens Axboe <axboe@kernel.dk>

[ Upstream commit 5aac0390a63b8718237a61dd0d24a29201d1c94a ]

tun only checks the file O_NONBLOCK flag, but it should also be checking
the iocb IOCB_NOWAIT flag. Any fops using ->read/write_iter() should check
both, otherwise it breaks users that correctly expect O_NONBLOCK semantics
if IOCB_NOWAIT is set.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/e9451860-96cc-c7c7-47b8-fe42cadd5f4c@kernel.dk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/tun.c |   14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1979,12 +1979,15 @@ static ssize_t tun_chr_write_iter(struct
 	struct tun_file *tfile = file->private_data;
 	struct tun_struct *tun = tun_get(tfile);
 	ssize_t result;
+	int noblock = 0;
 
 	if (!tun)
 		return -EBADFD;
 
-	result = tun_get_user(tun, tfile, NULL, from,
-			      file->f_flags & O_NONBLOCK, false);
+	if ((file->f_flags & O_NONBLOCK) || (iocb->ki_flags & IOCB_NOWAIT))
+		noblock = 1;
+
+	result = tun_get_user(tun, tfile, NULL, from, noblock, false);
 
 	tun_put(tun);
 	return result;
@@ -2203,10 +2206,15 @@ static ssize_t tun_chr_read_iter(struct
 	struct tun_file *tfile = file->private_data;
 	struct tun_struct *tun = tun_get(tfile);
 	ssize_t len = iov_iter_count(to), ret;
+	int noblock = 0;
 
 	if (!tun)
 		return -EBADFD;
-	ret = tun_do_read(tun, tfile, to, file->f_flags & O_NONBLOCK, NULL);
+
+	if ((file->f_flags & O_NONBLOCK) || (iocb->ki_flags & IOCB_NOWAIT))
+		noblock = 1;
+
+	ret = tun_do_read(tun, tfile, to, noblock, NULL);
 	ret = min_t(ssize_t, ret, len);
 	if (ret > 0)
 		iocb->ki_pos = ret;