On Tue, May 10, 2022 at 04:01:05PM +0800, Michael Wu wrote:
> 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] |
I assume this is the path through ffs_epfile_io() with !io_data->aio.
It looks like there is no check there for epfile->ep == ep which the
other paths do check.
Does the patch below fix the problem without needing to add a new
completion?
-- >8 --
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -1084,16 +1084,22 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
*/
usb_ep_dequeue(ep->ep, req);
wait_for_completion(&done);
- interrupted = ep->status < 0;
+ interrupted = true;
}
- if (interrupted)
+ spin_lock_irq(&epfile->ffs->eps_lock);
+ if (epfile->ep != ep)
+ ret = -ESHUTDOWN;
+ else if (interrupted && ep->status < 0)
ret = -EINTR;
- else if (io_data->read && ep->status > 0)
- ret = __ffs_epfile_read_data(epfile, data, ep->status,
- &io_data->data);
else
ret = ep->status;
+ spin_unlock_irq(&epfile->ffs->eps_lock);
+
+ if (io_data->read && ret > 0)
+ ret = __ffs_epfile_read_data(epfile, data, ret,
+ &io_data->data);
+
goto error_mutex;
} else if (!(req = usb_ep_alloc_request(ep->ep, GFP_ATOMIC))) {
ret = -ENOMEM;
