On Wed, 04 Oct 2023, Greg Kroah-Hartman wrote: > On Wed, Oct 04, 2023 at 10:09:18AM +0100, Lee Jones wrote: > > On Wed, 04 Oct 2023, Greg Kroah-Hartman wrote: > > > > > On Tue, Oct 03, 2023 at 07:55:00PM +0100, Lee Jones wrote: > > > > On Tue, 03 Oct 2023, Greg Kroah-Hartman wrote: > > > > > > > > > On Tue, Oct 03, 2023 at 06:00:20PM +0100, Lee Jones wrote: > > > > > > The important part of the call stack being: > > > > > > > > > > > > gsmld_write() # Takes a lock and disables IRQs > > > > > > con_write() > > > > > > console_lock() > > > > > > > > > > Wait, why is the n_gsm line discipline being used for a console? > > > > > > > > > > What hardware/protocol wants this to happen? > > > > > > > > > > gsm I thought was for a very specific type of device, not a console. > > > > > > > > > > As per: > > > > > https://www.kernel.org/doc/html/v5.9/driver-api/serial/n_gsm.html > > > > > this is a specific modem protocol, why is con_write() being called? > > > > > > > > What it's meant for and what random users can make it do are likely to > > > > be quite separate questions. This scenario is user driven and can be > > > > replicated simply by issuing a few syscalls (open, ioctl, write). > > > > > > I would recommend that any distro/system that does not want to support > > > this specific hardware protocol, just disable it for now (it's marked as > > > experimental too), if they don't want to deal with the potential > > > sleep-while-atomic issue. > > > > n_gsm is available on all the systems I have available. The mention of > > 'EXPERIMENTAL' in the module description appears to have zero effect on > > whether distros choose to make it available or not. If you're saying > > that we know this module is BROKEN however, then perhaps we should mark > > it as such. > > Also, I think this requires root to set this line discipline to the > console, right? A normal user can't do that, or am I missing a code > path here? I haven't been testing long, but yes, early indications show that root is required. > Is there a reproducer somewhere for this issue that runs as a normal > user? I couldn't find one in the syzbot listings but I might have been > not looking deep enough. https://syzkaller.appspot.com/text?tag=ReproC&x=15578d8fa80000 -- Lee Jones [李琼斯]
