Re: usb: f_fs: Fix CFI failure in ki_complete

[Dan Carpenter]

On Thu, Dec 22, 2022 at 06:21:03PM +0530, Prashanth K wrote:
> 
> 
> On 14-12-22 11:05 pm, David Laight wrote:
> > From: Greg Kroah-Hartman
> > > Sent: 12 December 2022 13:35
> > > 
> > > On Mon, Dec 12, 2022 at 06:54:24PM +0530, Prashanth K wrote:
> > > > Function pointer ki_complete() expects 'long' as its second
> > > > argument, but we pass integer from ffs_user_copy_worker. This
> > > > might cause a CFI failure, as ki_complete is an indirect call
> > > > with mismatched prototype. Fix this by typecasting the second
> > > > argument to long.
> > > 
> > > "might"?  Does it or not?  If it does, why hasn't this been reported
> > > before?
> > 
> > Does the cast even help at all.
> Actually I also have these same questions
> - why we haven't seen any instances other than this one?
> - why its not seen on other indirect function calls?
> 
> Here is the the call stack of the failure that we got.
> 
> [  323.288681][    T7] Kernel panic - not syncing: CFI failure (target:
> 0xffffffe5fc811f98)
> [  323.288710][    T7] CPU: 6 PID: 7 Comm: kworker/u16:0 Tainted: G S    W
> OE     5.15.41-android13-8-g5ffc5644bd20 #1
> [  323.288730][    T7] Workqueue: adb ffs_user_copy_worker.cfi_jt
> [  323.288752][    T7] Call trace:
> [  323.288755][    T7]  dump_backtrace.cfi_jt+0x0/0x8
> [  323.288772][    T7]  dump_stack_lvl+0x80/0xb8
> [  323.288785][    T7]  panic+0x180/0x444
> [  323.288797][    T7]  find_check_fn+0x0/0x218
> [  323.288810][    T7]  ffs_user_copy_worker+0x1dc/0x204
> [  323.288822][    T7]  kretprobe_trampoline.cfi_jt+0x0/0x8
> [  323.288837][    T7]  worker_thread+0x3ec/0x920
> [  323.288850][    T7]  kthread+0x168/0x1dc
> [  323.288859][    T7]  ret_from_fork+0x10/0x20
> [  323.288866][    T7] SMP: stopping secondary CPUs
> 
> And from address to line translation, we got know the issue is from
> ffs_user_copy_worker+0x1dc/0x204
> 		||
> io_data->kiocb->ki_complete(io_data->kiocb, ret);
> 
> And "find_check_fn" was getting invoked from ki_complete. Only thing that I
> found suspicious about ki_complete() is its argument types. That's why I
> pushed this patch here, so that we can discuss this out here.

I think the problem is more likely whatever ->ki_complete() points to
but I have no idea what that is on your system.  You're using an Android
kernel so it could be something out of tree as well...

regards,
dan carpenter