On arm64 android12 and possibly other platforms, during the usb gadget
function switching procedure (e.g. from mtp to midi), a synchronization
issue could occur, which causes an use-after-free panic as shown below:
[ 119.787946][ T1] init: Control message: Processed ctl.start for 'adbd' from pid: 395 (system_server)
[ 119.790006][ T32] android_work: sent uevent USB_STATE=DISCONNECTED
[ 119.805457][ T2309] usercopy: Kernel memory exposure attempt detected from SLUB object 'kmalloc-512' (offset 0, size 1802201963)!
[ 119.819368][ T2309] ------------[ cut here ]------------
[ 119.825359][ T2309] kernel BUG at mm/usercopy.c:99!
[ 119.830868][ T2309] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
[ 119.837843][ T2309] Modules linked in: sunxi_usbc ohci_sunxi ehci_sunxi sunxi_hci mali_kbase(O) sunxi_rfkill
[ 119.848904][ T2309] CPU: 3 PID: 2309 Comm: MtpServer Tainted: G O 5.4.125+ #9
[ 119.858411][ T2309] Hardware name: sun50iw9 (DT)
[ 119.863615][ T2309] pstate: 60400005 (nZCv daif +PAN -UAO)
[ 119.869790][ T2309] pc : usercopy_abort+0x90/0x94
[ 119.875078][ T2309] lr : usercopy_abort+0x90/0x94
[ 119.880357][ T2309] sp : ffffffc019e13ad0
[ 119.884858][ T2309] x29: ffffffc019e13ae0 x28: 0000000000000000
[ 119.891601][ T2309] x27: ffffff8030e7c030 x26: 0000000000000000
[ 119.898347][ T2309] x25: 0000000000000001 x24: ffffff806e25bd30
[ 119.905092][ T2309] x23: 000000006b6b6b6b x22: ffffff807c804680
[ 119.911838][ T2309] x21: ffffff8041410200 x20: 0000000000000001
[ 119.918581][ T2309] x19: 000000006b6b6b6b x18: ffffffc019e05058
[ 119.925326][ T2309] x17: 0000000000000000 x16: 00000000000002e3
[ 119.932073][ T2309] x15: 0000000000000000 x14: 0000000000000010
[ 119.938820][ T2309] x13: ffffffc0103972c0 x12: 0000000000000001
[ 119.945565][ T2309] x11: 0000000000000000 x10: 0000000000000002
[ 119.952311][ T2309] x9 : 54fea1fa84857d00 x8 : 54fea1fa84857d00
[ 119.959056][ T2309] x7 : 0000000000000001 x6 : 0000000000000000
[ 119.965801][ T2309] x5 : ffffff807f3a9038 x4 : 0000000000000000
[ 119.972546][ T2309] x3 : 0000000000000000 x2 : ffffff807f3a8f40
[ 119.979293][ T2309] x1 : ffffffc0114e94de x0 : 000000000000006d
[ 119.986038][ T2309] Call trace:
[ 119.989569][ T2309] usercopy_abort+0x90/0x94
[ 119.994466][ T2309] __check_heap_object+0x16c/0x188
[ 120.000041][ T2309] __check_object_size+0x120/0x210
[ 120.005620][ T2309] ffs_epfile_io+0x574/0x6bc
[ 120.010612][ T2309] ffs_epfile_read_iter+0x10c/0x198
[ 120.016284][ T2309] __vfs_read+0x178/0x1e0
[ 120.020980][ T2309] vfs_read+0x1d0/0x284
[ 120.025481][ T2309] ksys_read+0x74/0xe0
[ 120.029884][ T2309] __arm64_sys_read+0x1c/0x28
[ 120.034977][ T2309] el0_svc_common+0xb8/0x1cc
[ 120.039967][ T2309] el0_svc_compat_handler+0x1c/0x28
[ 120.045649][ T2309] el0_svc_compat+0x8/0x24
[ 120.050453][ T2309] Code: f90003e4 aa0803e1 aa0903e4 97fa0fa9 (d4210000)
[ 120.058109][ T2309] ---[ end trace a246be823ca7d164 ]---
[ 120.064073][ T2309] Kernel panic - not syncing: Fatal exception
[ 120.070723][ T2309] SMP: stopping secondary CPUs
[ 120.076030][ T2309] Kernel Offset: disabled
[ 120.080757][ T2309] CPU features: 0x00010002,20002004
[ 120.086438][ T2309] Memory Limit: none
[ 120.090657][ T2309] ---[ end Kernel panic - not syncing: Fatal exception ]---
Two processes P1 and P2 engaged in the switching procedure:
- P1 (e.g. MtpServer) calls 'ffs_epfile_io' (alias 'C'),
- P2 (e.g. usb@1.0-service) calls 'ffs_epfile_io_complete' (alias 'A')
and the 'ffs_func_unbind' (alias 'B').
P1 P2
| |
| configfs_write_file|
| gadget_dev_desc_UDC_store|
| unregister_gadget|
| usb_gadget_unregister_driver|
| usb_gadget_remove_driver|
| |
| |________________________________________
| | |
| usb_gadget_disconnect| |
| sunxi_udc_pullup| |
| sunxi_udc_set_pullup| |
| configfs_composite_disconnect| |
| composite_disconnect| |
| reset_config| |
| ffs_func_disable| |
| ffs_func_set_alt| |
| ffs_func_eps_disable| |
| usb_ep_disable| |
| sunxi_udc_ep_disable| |
| sunxi_udc_nuke| configfs_composite_unbind|
| sunxi_udc_done| |
| | |
|ffs_epfile_read_iter | purge_configs_funcs|
| | |
| complete | |
|ffs_epfile_io [C] <------------ |ffs_epfile_io_complete [A] |
| + | |
| + |
| + |
| + [1] complete |
| +++++++++++++++++++++++++++++++++++++++++++++++> ffs_func_unbind[B]|
| |
On gadget switching, 'A' will raise a completion, which wakes up 'P1' to
resume 'C'. Then 'C' references 'ep->status' for branch jumping etc.
On the other path, 'B' keeps running and exec 'kfree(func->eps)', which
actually free 'ep->status' referenced by 'C'.
This leads to the panic: `usercopy: Kernel memory exposure attempt detected
from SLUB object 'kmalloc-512' (offset 0, size 1802201963)!`
To fix this issue, we add a completion[1] to ensure that 'C' completes
before 'B'.
Signed-off-by: Michael Wu <michael@xxxxxxxxxxxxxxxxx>
---
drivers/usb/gadget/function/f_fs.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 4585ee3a444a8..c3e918cd00170 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -124,6 +124,7 @@ struct ffs_ep {
u8 num;
int status; /* P: epfile->mutex */
+ void *context;
};
struct ffs_epfile {
@@ -246,6 +247,7 @@ ffs_sb_create_file(struct super_block *sb, const char *name, void *data,
DEFINE_MUTEX(ffs_lock);
EXPORT_SYMBOL_GPL(ffs_lock);
+DECLARE_COMPLETION(io_done);
static struct ffs_dev *_ffs_find_dev(const char *name);
static struct ffs_dev *_ffs_alloc_dev(void);
@@ -711,6 +713,8 @@ static void ffs_epfile_io_complete(struct usb_ep *_ep, struct usb_request *req)
if (req->context) {
struct ffs_ep *ep = _ep->driver_data;
ep->status = req->status ? req->status : req->actual;
+ if (ep->status == -ESHUTDOWN)
+ ep->context = &io_done;
complete(req->context);
}
}
@@ -1094,6 +1098,10 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
&io_data->data);
else
ret = ep->status;
+
+ if (ep->status == -ESHUTDOWN && ep->context)
+ complete(ep->context);
+
goto error_mutex;
} else if (!(req = usb_ep_alloc_request(ep->ep, GFP_ATOMIC))) {
ret = -ENOMEM;
@@ -3607,6 +3615,12 @@ static void ffs_func_unbind(struct usb_configuration *c,
/* cleanup after autoconfig */
spin_lock_irqsave(&func->ffs->eps_lock, flags);
while (count--) {
+ if (ep->status == -ESHUTDOWN && ep->context) {
+ spin_unlock_irqrestore(&func->ffs->eps_lock, flags);
+ wait_for_completion(ep->context);
+ spin_lock_irqsave(&func->ffs->eps_lock, flags);
+ }
+
if (ep->ep && ep->req)
usb_ep_free_request(ep->ep, ep->req);
ep->req = NULL;
--
2.29.0
