From c584fb6d430e4b53c3282bd304817cb81ccf663e Mon Sep 17 00:00:00 2001 From: Alan Stern Date: Sat, 28 Mar 2020 16:18:11 -0400 Subject: [PATCH] USB: core: Fix free-while-in-use bug in the USB S-Glibrary commit 056ad39ee9253873522f6469c3364964a322912b upstream. 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. Mot-CRs-fixed: (CR) CVE-Fixed: CVE-2020-12464 Bug: 156071259 Signed-off-by: Alan Stern Reported-and-tested-by: Kyungtae Kim CC: Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.2003281615140.14837-100000@netrider.rowland.org Signed-off-by: Greg Kroah-Hartman Signed-off-by: Lee Jones Signed-off-by: Jignesh Patel Change-Id: I21aecc9aa1c604b05eb74bd3e46bcdb224af81fd Reviewed-on: https://gerrit.mot.com/1669824 SLTApproved: Slta Waiver SME-Granted: SME Approvals Granted Tested-by: Jira Key Reviewed-by: Xiangpo Zhao Submit-Approved: Jira Key (cherry picked from commit b41b21e2d7e39f6c8ac59f9422ed1b9a103ebfc9) --- 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 833ddd228e3a..0a793ab93907 100644 --- a/drivers/usb/core/message.c +++ b/drivers/usb/core/message.c @@ -586,12 +586,13 @@ 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) { @@ -605,6 +606,12 @@ 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); -- 2.20.1