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@xxxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxx>
Reported-and-tested-by: Kyungtae Kim <kt0755@xxxxxxxxx>
CC: <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.2003281615140.14837-100000@xxxxxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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);
--
2.26.1
