This is a note to let you know that I've just added the patch titled

USB: core: Fix free-while-in-use bug in the USB S-Glibrary

to my usb git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 056ad39ee9253873522f6469c3364964a322912b Mon Sep 17 00:00:00 2001

From: Alan Stern stern@rowland.harvard.edu Date: Sat, 28 Mar 2020 16:18:11 -0400 Subject: USB: core: Fix free-while-in-use bug in the USB S-Glibrary

FuzzUSB (a variant of syzkaller) found a free-while-still-in-use bug in the USB scatter-gather library:

BUG: KASAN: use-after-free in atomic_read include/asm-generic/atomic-instrumented.h:26 [inline] BUG: KASAN: use-after-free in usb_hcd_unlink_urb+0x5f/0x170 drivers/usb/core/hcd.c:1607 Read of size 4 at addr ffff888065379610 by task kworker/u4:1/27

CPU: 1 PID: 27 Comm: kworker/u4:1 Not tainted 5.5.11 #2 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014 Workqueue: scsi_tmf_2 scmd_eh_abort_handler Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0xce/0x128 lib/dump_stack.c:118 print_address_description.constprop.4+0x21/0x3c0 mm/kasan/report.c:374 __kasan_report+0x153/0x1cb mm/kasan/report.c:506 kasan_report+0x12/0x20 mm/kasan/common.c:639 check_memory_region_inline mm/kasan/generic.c:185 [inline] check_memory_region+0x152/0x1b0 mm/kasan/generic.c:192 __kasan_check_read+0x11/0x20 mm/kasan/common.c:95 atomic_read include/asm-generic/atomic-instrumented.h:26 [inline] usb_hcd_unlink_urb+0x5f/0x170 drivers/usb/core/hcd.c:1607 usb_unlink_urb+0x72/0xb0 drivers/usb/core/urb.c:657 usb_sg_cancel+0x14e/0x290 drivers/usb/core/message.c:602 usb_stor_stop_transport+0x5e/0xa0 drivers/usb/storage/transport.c:937

This bug occurs when cancellation of the S-G transfer races with transfer completion. When that happens, usb_sg_cancel() may continue to access the transfer's URBs after usb_sg_wait() has freed them.

The bug is caused by the fact that usb_sg_cancel() does not take any sort of reference to the transfer, and so there is nothing to prevent the URBs from being deallocated while the routine is trying to use them. The fix is to take such a reference by incrementing the transfer's io->count field while the cancellation is in progres and decrementing it afterward. The transfer's URBs are not deallocated until io->complete is triggered, which happens when io->count reaches zero.

Signed-off-by: Alan Stern stern@rowland.harvard.edu Reported-and-tested-by: Kyungtae Kim kt0755@gmail.com CC: stable@vger.kernel.org

Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.2003281615140.14837-100000@netride... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/core/message.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c index d5f834f16993..a48678a0c83a 100644 --- a/drivers/usb/core/message.c +++ b/drivers/usb/core/message.c @@ -589,12 +589,13 @@ void usb_sg_cancel(struct usb_sg_request *io) int i, retval;

spin_lock_irqsave(&io->lock, flags); - if (io->status) { + if (io->status || io->count == 0) { spin_unlock_irqrestore(&io->lock, flags); return; } /* shut everything down */ io->status = -ECONNRESET; + io->count++; /* Keep the request alive until we're done */ spin_unlock_irqrestore(&io->lock, flags);

for (i = io->entries - 1; i >= 0; --i) { @@ -608,6 +609,12 @@ void usb_sg_cancel(struct usb_sg_request *io) dev_warn(&io->dev->dev, "%s, unlink --> %d\n", __func__, retval); } + + spin_lock_irqsave(&io->lock, flags); + io->count--; + if (!io->count) + complete(&io->complete); + spin_unlock_irqrestore(&io->lock, flags); } EXPORT_SYMBOL_GPL(usb_sg_cancel);