linux-kernel - [PATCH 3.16 095/178] virtio_balloon: prevent uninitialized variable use

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Date:   Sun, 16 Jul 2017 14:56:46 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Ladi Prosek" <lprosek@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "Arnd Bergmann" <arnd@...db.de>
Subject: [PATCH 3.16 095/178] virtio_balloon: prevent uninitialized
 variable use

3.16.46-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Arnd Bergmann <arnd@...db.de>

commit f0bb2d50dfcc519f06f901aac88502be6ff1df2c upstream.

The latest gcc-7.0.1 snapshot reports a new warning:

virtio/virtio_balloon.c: In function 'update_balloon_stats':
virtio/virtio_balloon.c:258:26: error: 'events[2]' is used uninitialized in this function [-Werror=uninitialized]
virtio/virtio_balloon.c:260:26: error: 'events[3]' is used uninitialized in this function [-Werror=uninitialized]
virtio/virtio_balloon.c:261:56: error: 'events[18]' is used uninitialized in this function [-Werror=uninitialized]
virtio/virtio_balloon.c:262:56: error: 'events[17]' is used uninitialized in this function [-Werror=uninitialized]

This seems absolutely right, so we should add an extra check to
prevent copying uninitialized stack data into the statistics.
>>From all I can tell, this has been broken since the statistics code
was originally added in 2.6.34.

Fixes: 9564e138b1f6 ("virtio: Add memory statistics reporting to the balloon driver (V4)")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Ladi Prosek <lprosek@...hat.com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/virtio/virtio_balloon.c | 2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -218,12 +218,14 @@ static void update_balloon_stats(struct
 	all_vm_events(events);
 	si_meminfo(&i);
 
+#ifdef CONFIG_VM_EVENT_COUNTERS
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
 				pages_to_bytes(events[PSWPIN]));
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
 				pages_to_bytes(events[PSWPOUT]));
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
+#endif
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
 				pages_to_bytes(i.freeram));
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,