[PATCH v2] usb: raw-gadget: fix UAF in raw_process_ep_io
From: Drif Abdelmalek Mohamed Said
Date: Sat Sep 26 2026 - 07:32:39 EST
syzbot reported
BUG: KASAN: slab-use-after-free in string_nocheck lib/vsprintf.c:648 [inline]
BUG: KASAN: slab-use-after-free in string+0x471/0x4d0 lib/vsprintf.c:730
Read of size 1 at addr ffff88802c217340 by task syz-executor384/5947
CPU: 1 UID: 0 PID: 5947 Comm: syz-executor384 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0x13d/0x4b0 mm/kasan/report.c:482
kasan_report+0xdf/0x1c0 mm/kasan/report.c:595
string_nocheck lib/vsprintf.c:648 [inline]
string+0x471/0x4d0 lib/vsprintf.c:730
vsnprintf+0x422/0x1300 lib/vsprintf.c:2945
snprintf+0xc7/0x100 lib/vsprintf.c:3043
set_dev_info drivers/base/core.c:4984 [inline]
dev_vprintk_emit+0x375/0x3e0 drivers/base/core.c:4994
dev_printk_emit+0xd2/0x10d drivers/base/core.c:5007
__dev_printk+0xcb/0x100 drivers/base/core.c:5019
_dev_err+0xef/0x127 drivers/base/core.c:5062
raw_process_ep_io.cold+0x43/0x83 drivers/usb/gadget/legacy/raw_gadget.c:1116
raw_ioctl_ep_write drivers/usb/gadget/legacy/raw_gadget.c:1153 [inline]
raw_ioctl+0x25a/0x2b80 drivers/usb/gadget/legacy/raw_gadget.c:1325
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl fs/ioctl.c:583 [inline]
__x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc86effa5eb
Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48
Code: 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05
Code: <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00
RSP: 002b:00007ffcab99fea0 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fc86effa5eb
RDX: 00007ffcab99ff14 RSI: 0000000040085507 RDI: 0000000000000003
RBP: 0000000000000004 R08: 0000000000000000 R09: 0000000000000000
R10: 00007ffcab99fec0 R11: 0000000000000246 R12: 0000000000000003
R13: 00007ffcab99ff08 R14: 00007fc86f07dcc0 R15: 0000000000000002
</TASK>
Allocated by task 1:
kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
kasan_save_track+0x14/0x30 mm/kasan/common.c:78
poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
__kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:415
kasan_kmalloc include/linux/kasan.h:263 [inline]
__do_kmalloc_node mm/slub.c:5334 [inline]
__kmalloc_node_track_caller_noprof+0x331/0x830 mm/slub.c:5471
kvasprintf+0xbc/0x150 lib/kasprintf.c:25
kvasprintf_const+0x66/0x1a0 lib/kasprintf.c:49
kobject_set_name_vargs+0x5a/0x140 lib/kobject.c:274
dev_set_name+0xc7/0x100 drivers/base/core.c:3560
usb_add_gadget+0x520/0x920 drivers/usb/gadget/udc/core.c:1459
usb_add_gadget_udc_release drivers/usb/gadget/udc/core.c:1517 [inline]
usb_add_gadget_udc+0x26/0x70 drivers/usb/gadget/udc/core.c:1564
dummy_udc_probe+0x69e/0x960 drivers/usb/gadget/udc/dummy_hcd.c:1121
platform_probe+0x106/0x1d0 drivers/base/platform.c:1439
call_driver_probe drivers/base/dd.c:628 [inline]
really_probe+0x241/0xa60 drivers/base/dd.c:706
__driver_probe_device+0x20e/0x450 drivers/base/dd.c:868
driver_probe_device+0x4a/0x140 drivers/base/dd.c:898
__device_attach_driver+0x1df/0x320 drivers/base/dd.c:1026
bus_for_each_drv+0x159/0x1e0 drivers/base/bus.c:500
__device_attach+0x1e4/0x4d0 drivers/base/dd.c:1098
device_initial_probe+0xaf/0xd0 drivers/base/dd.c:1153
bus_probe_device+0x64/0x160 drivers/base/bus.c:620
device_add+0x121d/0x1970 drivers/base/core.c:3772
platform_device_add+0x35a/0x800 drivers/base/platform.c:762
dummy_hcd_init+0x803/xc00 drivers/usb/gadget/udc/dummy_hcd.c:2894
do_one_initcall+0x11d/0x700 init/main.c:1347
do_initcall_level init/main.c:1409 [inline]
do_initcalls init/main.c:1425 [inline]
do_basic_setup init/main.c:1445 [inline]
kernel_init_freeable+0x6ea/0x7b0 init/main.c:1658
kernel_init+0x1f/0x1e0 init/main.c:1548
ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
Freed by task 5947:
kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
kasan_save_track+0x14/0x30 mm/kasan/common.c:78
kasan_save_free_info+0x3b/0x70 mm/kasan/generic.c:584
poison_slab_object mm/kasan/common.c:253 [inline]
__kasan_slab_free+0x5f/0x80 mm/kasan/common.c:285
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:2677 [inline]
slab_free mm/slub.c:6377 [inline]
kfree+0x22b/0x6c0 mm/slub.c:6692
kfree_const+0x5a/0x70 mm/util.c:46
kobject_cleanup lib/kobject.c:695 [inline]
kobject_release lib/kobject.c:720 [inline]
kref_put include/linux/kref.h:65 [inline]
kobject_put+0x218/0x640 lib/kobject.c:737
put_device+0x1f/0x30 drivers/base/core.c:3880
platform_remove+0x5f/0x80 drivers/base/platform.c:1456
device_remove+0xcb/0x180 drivers/base/dd.c:616
__device_release_driver drivers/base/dd.c:1349 [inline]
device_release_driver_internal+0x44e/0x620 drivers/base/dd.c:1372
unbind_store+0xf8/0x110 drivers/base/bus.c:244
drv_attr_store+0x74/0xb0 drivers/base/bus.c:125
sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x6ac/0x1050 fs/read_write.c:687
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
When the UDC backing a raw-gadget instance is unbound, the UDC core
unregisters the gadget and frees the struct usb_gadget. gadget_unbind is
eventually called but there still remains a dangling pointer for the
gadget in raw_dev. Because the fd for raw_gadget is still open, a
reference to it remains. Following calls from ioctl would pass the
checks. When usb_ep_queue fails, it calls dev_err with dev->gadget->dev.
Since gadget is freed, this causes a UAF.
To fix it, we simply nullify dev->gadget in gadget_unbind. This requires
a spinlock.
Reported-by: syzbot+596b59aea1a9deaaab67@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=596b59aea1a9deaaab67
Tested-by: syzbot+596b59aea1a9deaaab67@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Drif Abdelmalek Mohamed Said <drifabdelmalekmohamedsaid@xxxxxxxxx>
---
v2:
-fixed a typo, added syzbot to cc to get tracked by dashboard, my bad.
drivers/usb/gadget/legacy/raw_gadget.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/usb/gadget/legacy/raw_gadget.c b/drivers/usb/gadget/legacy/raw_gadget.c
index 4febf8dac7ca..9c263950f609 100644
--- a/drivers/usb/gadget/legacy/raw_gadget.c
+++ b/drivers/usb/gadget/legacy/raw_gadget.c
@@ -327,9 +327,16 @@ static int gadget_bind(struct usb_gadget *gadget,
static void gadget_unbind(struct usb_gadget *gadget)
{
+ unsigned long flags;
struct raw_dev *dev = get_gadget_data(gadget);
set_gadget_data(gadget, NULL);
+
+ /* Avoid dangling pointer in case of remaining references */
+ spin_lock_irqsave(&dev->lock, flags);
+ dev->gadget = NULL;
+ spin_unlock_irqrestore(&dev->lock, flags);
+
/* Matches kref_get() in gadget_bind(). */
kref_put(&dev->count, dev_free);
}
--
2.43.0