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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, Cornelia Huck <cohuck@redhat.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Vasily Averin <vvs@virtuozzo.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.9 61/88] s390/cio: cio_ignore_proc_seq_next should increase position index
Date:   Tue, 10 Mar 2020 13:39:09 +0100
Message-Id: <20200310123621.642063499@linuxfoundation.org>
In-Reply-To: <20200310123606.543939933@linuxfoundation.org>
References: <20200310123606.543939933@linuxfoundation.org>
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From: Vasily Averin <vvs@virtuozzo.com>

[ Upstream commit 8b101a5e14f2161869636ff9cb4907b7749dc0c2 ]

if seq_file .next fuction does not change position index,
read after some lseek can generate unexpected output.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=206283
Link: https://lore.kernel.org/r/d44c53a7-9bc1-15c7-6d4a-0c10cb9dffce@virtuozzo.com
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/s390/cio/blacklist.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/cio/blacklist.c b/drivers/s390/cio/blacklist.c
index 9082476b51db9..4e9f794176d35 100644
--- a/drivers/s390/cio/blacklist.c
+++ b/drivers/s390/cio/blacklist.c
@@ -302,8 +302,10 @@ static void *
 cio_ignore_proc_seq_next(struct seq_file *s, void *it, loff_t *offset)
 {
 	struct ccwdev_iter *iter;
+	loff_t p = *offset;
 
-	if (*offset >= (__MAX_SUBCHANNEL + 1) * (__MAX_SSID + 1))
+	(*offset)++;
+	if (p >= (__MAX_SUBCHANNEL + 1) * (__MAX_SSID + 1))
 		return NULL;
 	iter = it;
 	if (iter->devno == __MAX_SUBCHANNEL) {
@@ -313,7 +315,6 @@ cio_ignore_proc_seq_next(struct seq_file *s, void *it, loff_t *offset)
 			return NULL;
 	} else
 		iter->devno++;
-	(*offset)++;
 	return iter;
 }
 
-- 
2.20.1