[PATCH 3.12 079/235] USB: gadgetfs: fix unbounded memory allocation bug

From: Jiri Slaby
Date: Fri Jan 27 2017 - 06:54:01 EST

From: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>

3.12-stable review patch. If anyone has any objections, please let me know.


commit faab50984fe6636e616c7cc3d30308ba391d36fd upstream.

Andrey Konovalov reports that fuzz testing with syzkaller causes a
KASAN warning in gadgetfs:

BUG: KASAN: slab-out-of-bounds in dev_config+0x86f/0x1190 at addr ffff88003c47e160
Write of size 65537 by task syz-executor0/6356
CPU: 3 PID: 6356 Comm: syz-executor0 Not tainted 4.9.0-rc7+ #19
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
ffff88003c107ad8 ffffffff81f96aba ffffffff3dc11ef0 1ffff10007820eee
ffffed0007820ee6 ffff88003dc11f00 0000000041b58ab3 ffffffff8598b4c8
ffffffff81f96828 ffffffff813fb4a0 ffff88003b6eadc0 ffff88003c107738
Call Trace:
[< inline >] __dump_stack lib/dump_stack.c:15
[<ffffffff81f96aba>] dump_stack+0x292/0x398 lib/dump_stack.c:51
[<ffffffff817e4dec>] kasan_object_err+0x1c/0x70 mm/kasan/report.c:159
[< inline >] print_address_description mm/kasan/report.c:197
[<ffffffff817e5080>] kasan_report_error+0x1f0/0x4e0 mm/kasan/report.c:286
[<ffffffff817e5705>] kasan_report+0x35/0x40 mm/kasan/report.c:306
[< inline >] check_memory_region_inline mm/kasan/kasan.c:308
[<ffffffff817e3fb9>] check_memory_region+0x139/0x190 mm/kasan/kasan.c:315
[<ffffffff817e4044>] kasan_check_write+0x14/0x20 mm/kasan/kasan.c:326
[< inline >] copy_from_user arch/x86/include/asm/uaccess.h:689
[< inline >] ep0_write drivers/usb/gadget/legacy/inode.c:1135
[<ffffffff83228caf>] dev_config+0x86f/0x1190 drivers/usb/gadget/legacy/inode.c:1759
[<ffffffff817fdd55>] __vfs_write+0x5d5/0x760 fs/read_write.c:510
[<ffffffff817ff650>] vfs_write+0x170/0x4e0 fs/read_write.c:560
[< inline >] SYSC_write fs/read_write.c:607
[<ffffffff81803a5b>] SyS_write+0xfb/0x230 fs/read_write.c:599
[<ffffffff84f47ec1>] entry_SYSCALL_64_fastpath+0x1f/0xc2

Indeed, there is a comment saying that the value of len is restricted
to a 16-bit integer, but the code doesn't actually do this.

This patch fixes the warning. It replaces the comment with a
computation that forces the amount of data copied from the user in
ep0_write() to be no larger than the wLength size for the control
transfer, which is a 16-bit quantity.

Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Reported-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Tested-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Signed-off-by: Felipe Balbi <felipe.balbi@xxxxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
drivers/usb/gadget/inode.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/inode.c b/drivers/usb/gadget/inode.c
index 2b56e59a413f..6a6ef2160e7e 100644
--- a/drivers/usb/gadget/inode.c
+++ b/drivers/usb/gadget/inode.c
@@ -1199,7 +1199,7 @@ ep0_write (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
/* data and/or status stage for control request */
} else if (dev->state == STATE_DEV_SETUP) {

- /* IN DATA+STATUS caller makes len <= wLength */
+ len = min_t(size_t, len, dev->setup_wLength);
if (dev->setup_in) {
retval = setup_req (dev->gadget->ep0, dev->req, len);
if (retval == 0) {