netdev - [PATCH net 2/5] netdevsim: fix stack-out-of-bounds in nsim_dev_debugfs

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Date:   Sat, 11 Jan 2020 16:37:09 +0000
From:   Taehee Yoo <ap420073@...il.com>
To:     davem@...emloft.net, jakub.kicinski@...ronome.com,
        netdev@...r.kernel.org
Cc:     ap420073@...il.com
Subject: [PATCH net 2/5] netdevsim: fix stack-out-of-bounds in nsim_dev_debugfs_init()

When netdevsim dev is being created, a debugfs directory is created.
The variable "dev_ddir_name" is 16bytes device name pointer and device
name is "netdevsim<dev id>".
The maximum dev id length is 10.
So, 16bytes for device name isn't enough.

Test commands:
    modprobe netdevsim
    echo "1000000000 0" > /sys/bus/netdevsim/new_device

Splat looks like:
[   90.624922][ T1000] BUG: KASAN: stack-out-of-bounds in number+0x824/0x880
[   90.626999][ T1000] Write of size 1 at addr ffff8880b7f47988 by task bash/1000
[   90.627798][ T1000]
[   90.628076][ T1000] CPU: 0 PID: 1000 Comm: bash Not tainted 5.5.0-rc5+ #270
[   90.628806][ T1000] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
[   90.629752][ T1000] Call Trace:
[   90.630080][ T1000]  dump_stack+0x96/0xdb
[   90.630512][ T1000]  ? number+0x824/0x880
[   90.630939][ T1000]  print_address_description.constprop.5+0x1be/0x360
[   90.631610][ T1000]  ? number+0x824/0x880
[   90.632038][ T1000]  ? number+0x824/0x880
[   90.632469][ T1000]  __kasan_report+0x12a/0x16f
[   90.632939][ T1000]  ? number+0x824/0x880
[   90.633397][ T1000]  kasan_report+0xe/0x20
[   90.633954][ T1000]  number+0x824/0x880
[   90.634513][ T1000]  ? put_dec+0xa0/0xa0
[   90.635047][ T1000]  ? rcu_read_lock_sched_held+0x90/0xc0
[   90.636469][ T1000]  vsnprintf+0x63c/0x10b0
[   90.637187][ T1000]  ? pointer+0x5b0/0x5b0
[   90.637871][ T1000]  ? mark_lock+0x11d/0xc40
[   90.638591][ T1000]  sprintf+0x9b/0xd0
[   90.639164][ T1000]  ? scnprintf+0xe0/0xe0
[   90.639802][ T1000]  nsim_dev_probe+0x63c/0xbf0 [netdevsim]
[ ... ]

Fixes: 83c9e13aa39a ("netdevsim: add software driver for testing offloads")
Signed-off-by: Taehee Yoo <ap420073@...il.com>
---
 drivers/net/netdevsim/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/netdevsim/dev.c b/drivers/net/netdevsim/dev.c
index 634eb5cdcbbe..a0c80a70bb23 100644
--- a/drivers/net/netdevsim/dev.c
+++ b/drivers/net/netdevsim/dev.c
@@ -88,7 +88,7 @@ static const struct file_operations nsim_dev_take_snapshot_fops = {
 
 static int nsim_dev_debugfs_init(struct nsim_dev *nsim_dev)
 {
-	char dev_ddir_name[16];
+	char dev_ddir_name[32];
 
 	sprintf(dev_ddir_name, DRV_NAME "%u", nsim_dev->nsim_bus_dev->dev.id);
 	nsim_dev->ddir = debugfs_create_dir(dev_ddir_name, nsim_dev_ddir);
-- 
2.17.1