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USB: Fix "slab-out-of-bounds Write" bug in usb_hcd_poll_rh_status 

When the USB core code for getting root-hub status reports was
originally written, it was assumed that the hub driver would be its
only caller.  But this isn't true now; user programs can use usbfs to
communicate with root hubs and get status reports.  When they do this,
they may use a transfer_buffer that is smaller than the data returned
by the HCD, which will lead to a buffer overflow error when
usb_hcd_poll_rh_status() tries to store the status data.  This was
discovered by syzbot:

BUG: KASAN: slab-out-of-bounds in memcpy include/linux/fortify-string.h:225 [inline]
BUG: KASAN: slab-out-of-bounds in usb_hcd_poll_rh_status+0x5f4/0x780 drivers/usb/core/hcd.c:776
Write of size 2 at addr ffff88801da403c0 by task syz-executor133/4062

This patch fixes the bug by reducing the amount of status data if it
won't fit in the transfer_buffer.  If some data gets discarded then
the URB's completion status is set to -EOVERFLOW rather than 0, to let
the user know what happened.

Reported-and-tested-by: syzbot+3ae6a2b06f131ab9849f@syzkaller.appspotmail.com
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/Yc+3UIQJ2STbxNua@rowland.harvard.edu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Alan Stern 2021-12-31 21:07:12 -05:00 committed by Greg Kroah-Hartman
parent fa0ef93868
commit 1d7d4c0793
1 changed files with 8 additions and 1 deletions
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9
drivers/usb/core/hcd.c
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@ -753,6 +753,7 @@ void usb_hcd_poll_rh_status(struct usb_hcd *hcd)
{ {
struct urb *urb; struct urb *urb;
int length; int length;
int status;
unsigned long flags; unsigned long flags;
char buffer[6]; /* Any root hubs with > 31 ports? */ char buffer[6]; /* Any root hubs with > 31 ports? */
@ -770,11 +771,17 @@ void usb_hcd_poll_rh_status(struct usb_hcd *hcd)
if (urb) { if (urb) {
clear_bit(HCD_FLAG_POLL_PENDING, &hcd->flags); clear_bit(HCD_FLAG_POLL_PENDING, &hcd->flags);
hcd->status_urb = NULL; hcd->status_urb = NULL;
if (urb->transfer_buffer_length >= length) {
status = 0;
} else {
status = -EOVERFLOW;
length = urb->transfer_buffer_length;
}
urb->actual_length = length; urb->actual_length = length;
memcpy(urb->transfer_buffer, buffer, length); memcpy(urb->transfer_buffer, buffer, length);
usb_hcd_unlink_urb_from_ep(hcd, urb); usb_hcd_unlink_urb_from_ep(hcd, urb);
usb_hcd_giveback_urb(hcd, urb, 0); usb_hcd_giveback_urb(hcd, urb, status);
} else { } else {
length = 0; length = 0;
set_bit(HCD_FLAG_POLL_PENDING, &hcd->flags); set_bit(HCD_FLAG_POLL_PENDING, &hcd->flags);