Re: [PATCH 1/2] tty: vcc: zero-initialize control packet in vcc_send_ctl()
From: Jiri Slaby
Date: Fri Jul 31 2026 - 05:23:53 EST
On 31. 07. 26, 10:32, Greg Kroah-Hartman wrote:
On Fri, Jul 31, 2026 at 10:29:14AM +0200, Jiri Slaby wrote:
On 31. 07. 26, 10:15, Greg Kroah-Hartman wrote:
From: Joshua Rogers <linux@xxxxxxxxx>
The stack-allocated struct vio_vcc pkt was partially initialized,
leaving the tag.stype_env field uninitialized before being sent via
ldc_write(), potentially leaking kernel stack data to the LDC peer.
Assisted-by: AISLE:Snapshot
Cc: stable <stable@xxxxxxxxxx>
Signed-off-by: Joshua Rogers <linux@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/vcc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/tty/vcc.c b/drivers/tty/vcc.c
index 27a55465bf5e..3947bd2b75ac 100644
--- a/drivers/tty/vcc.c
+++ b/drivers/tty/vcc.c
@@ -492,7 +492,7 @@ static ssize_t domain_show(struct device *dev,
static int vcc_send_ctl(struct vcc_port *port, int ctl)
{
- struct vio_vcc pkt;
+ struct vio_vcc pkt = {};
Note this needs not initialize holes.
Does it? I keep forgetting this if it's really true or not. I think
we've been through this in the past but I can't find the archives.
I believe there are none here, but memset() is usually
preferred/safer.
Last I remember, a long time ago, the compiler would just use memset()
for this, and hit the holes. Or is that a compiler-specific issue?
Yes, it's more obvious, and I'll be glad to change it, but figuring this
out for real would be great :)
OK, so the standard (C17) does not guarantee zeroing.
What I found though:
* both clang and gcc zero the full struct for "{}". There was a bug in gcc < 8 where it did not.
* this is not true for designated initializer, cf. ce50039be49e ("net: sched: act_ife: initialize struct tc_ife to fix KMSAN kernel-infoleak")).
Adding Kees who is the author of:
====
Memory initialization
---------------------
Memory copied to userspace must always be fully initialized. If not
explicitly memset(), this will require changes to the compiler to make
sure structure holes are cleared.
====
He might aware of more bugs.
FWIW, {} here should be safe for two reasons:
* not a designated initializer
* no holes (IMO)
thanks,
--
js
suse labs