s390/cio: cio_ignore_proc_seq_next should increase position index

[ 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>

diff --git a/drivers/s390/cio/blacklist.c b/drivers/s390/cio/blacklist.c
index 9082476b51db9122a8a41186e7e40e1a97172368..4e9f794176d3511fc461af23b00aea5b174fb6c7 100644 (file)
--- 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;
 }