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Message-Id: <20241109152821.3476218-1-snovitoll@gmail.com>
Date: Sat, 9 Nov 2024 20:28:21 +0500
From: Sabyrzhan Tasbolatov <snovitoll@...il.com>
To: syzbot+9760fbbd535cee131f81@...kaller.appspotmail.com
Cc: gregkh@...uxfoundation.org,
linux-kernel@...r.kernel.org,
linux-usb@...r.kernel.org,
syzkaller-bugs@...glegroups.com,
oneukum@...e.com,
snovitoll@...il.com
Subject: [PATCH] usb/cdc-wdm: fix memory leak of wdm_device
syzbot reported "KMSAN: kernel-infoleak in wdm_read", though there is no
reproducer and the only report for this issue. This might be
a false-positive, but while the reading the code, it seems,
there is the way to leak kernel memory.
Here what I understand so far from the report happening
with ubuf in drivers/usb/class/cdc-wdm.c:
1. kernel buffer "ubuf" is allocated during cdc-wdm device creation in
the "struct wdm_device":
static int wdm_create()
{
...
desc->ubuf = kmalloc(desc->wMaxCommand, GFP_KERNEL);
...
usb_fill_control_urb(
...
wdm_in_callback,
...
);
}
2. during wdm_create() it calls wdm_in_callback() which MAY fill "ubuf"
for the first time via memmove if conditions are met.
static void wdm_in_callback()
{
...
if (length + desc->length > desc->wMaxCommand) {
...
} else {
/* we may already be in overflow */
if (!test_bit(WDM_OVERFLOW, &desc->flags)) {
memmove(desc->ubuf + desc->length, desc->inbuf, length);
desc->length += length;
desc->reslength = length;
}
}
...
}
3. if conditions are not fulfilled in step 2., then calling read() syscall
which calls wdm_read(), should leak the random kernel memory via
copy_to_user() from "ubuf" buffer which is allocated in kmalloc-256.
static ssize_t wdm_read()
{
...
struct wdm_device *desc = file->private_data;
cntr = READ_ONCE(desc->length);
...
if (cntr > count)
cntr = count;
rv = copy_to_user(buffer, desc->ubuf, cntr);
...
}
, where wMaxCommand is 256, AFAIU.
syzbot report
=============
BUG: KMSAN: kernel-infoleak in instrument_copy_to_user include/linux/instrumented.h:114 [inline]
BUG: KMSAN: kernel-infoleak in _inline_copy_to_user include/linux/uaccess.h:180 [inline]
BUG: KMSAN: kernel-infoleak in _copy_to_user+0xbc/0x110 lib/usercopy.c:26
instrument_copy_to_user include/linux/instrumented.h:114 [inline]
_inline_copy_to_user include/linux/uaccess.h:180 [inline]
_copy_to_user+0xbc/0x110 lib/usercopy.c:26
copy_to_user include/linux/uaccess.h:209 [inline]
wdm_read+0x227/0x1270 drivers/usb/class/cdc-wdm.c:603
vfs_read+0x2a1/0xf60 fs/read_write.c:474
ksys_read+0x20f/0x4c0 fs/read_write.c:619
__do_sys_read fs/read_write.c:629 [inline]
__se_sys_read fs/read_write.c:627 [inline]
__x64_sys_read+0x93/0xe0 fs/read_write.c:627
x64_sys_call+0x3055/0x3ba0 arch/x86/include/generated/asm/syscalls_64.h:1
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Reported-by: syzbot+9760fbbd535cee131f81@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9760fbbd535cee131f81
Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@...il.com>
---
drivers/usb/class/cdc-wdm.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
index 86ee39db013f..8801e03196de 100644
--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -1063,7 +1063,7 @@ static int wdm_create(struct usb_interface *intf, struct usb_endpoint_descriptor
if (!desc->command)
goto err;
- desc->ubuf = kmalloc(desc->wMaxCommand, GFP_KERNEL);
+ desc->ubuf = kzalloc(desc->wMaxCommand, GFP_KERNEL);
if (!desc->ubuf)
goto err;
--
2.34.1
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