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Subject[PATCH] Fix: buffer overflow during hvc_alloc().
Date
From: Andrew Melnychenko <andrew@daynix.com>

If there is a lot(more then 16) of virtio-console devices
or virtio_console module is reloaded
- buffers 'vtermnos' and 'cons_ops' are overflowed.
In older kernels it overruns spinlock which leads to kernel freezing:
https://bugzilla.redhat.com/show_bug.cgi?id=1786239

Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
---
drivers/tty/hvc/hvc_console.c | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index 27284a2dcd2b..436cc51c92c3 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -302,10 +302,6 @@ int hvc_instantiate(uint32_t vtermno, int index, const struct hv_ops *ops)
vtermnos[index] = vtermno;
cons_ops[index] = ops;

- /* reserve all indices up to and including this index */
- if (last_hvc < index)
- last_hvc = index;
-
/* check if we need to re-register the kernel console */
hvc_check_console(index);

@@ -960,13 +956,22 @@ struct hvc_struct *hvc_alloc(uint32_t vtermno, int data,
cons_ops[i] == hp->ops)
break;

- /* no matching slot, just use a counter */
- if (i >= MAX_NR_HVC_CONSOLES)
- i = ++last_hvc;
+ if (i >= MAX_NR_HVC_CONSOLES) {
+
+ /* find 'empty' slot for console */
+ for (i = 0; i < MAX_NR_HVC_CONSOLES && vtermnos[i] != -1; i++) {
+ }
+
+ /* no matching slot, just use a counter */
+ if (i == MAX_NR_HVC_CONSOLES)
+ i = ++last_hvc + MAX_NR_HVC_CONSOLES;
+ }

hp->index = i;
- cons_ops[i] = ops;
- vtermnos[i] = vtermno;
+ if (i < MAX_NR_HVC_CONSOLES) {
+ cons_ops[i] = ops;
+ vtermnos[i] = vtermno;
+ }

list_add_tail(&(hp->next), &hvc_structs);
mutex_unlock(&hvc_structs_mutex);
--
2.24.1
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