Messages in this thread | | | From | Nicolai Stange <> | Subject | Re: [PATCH v6 2/8] debugfs: prevent access to removed files' private data | Date | Sat, 21 May 2016 19:57:38 +0200 |
| |
Sasha Levin <sasha.levin@oracle.com> writes:
> On 05/18/2016 12:05 PM, Greg Kroah-Hartman wrote: >> On Wed, May 18, 2016 at 11:18:16AM -0400, Sasha Levin wrote: >>> On 05/18/2016 11:01 AM, Nicolai Stange wrote: >>>> Thanks a million for reporting! >>>> >>>> 1.) Do you have lockdep enabled? >>> >>> Yup, nothing there. >>> >>>> 2.) Does this happen before or after userspace init has been spawned, >>>> i.e. does the lockup happen at debugfs file creation time or >>>> possibly at usage time? >>> >>> So I looked closer, and it seems to happen after starting syzkaller, which >>> as far as I know tries to open many different debugfs files. >>> >>> Is there debug code I can add it that'll help us figure out what's up? >> >> Trying to figure out _which_ debugfs file is causing this would be >> great, if at all possible. strace? > > What seems to be failing is syzkaller's attempt to mmap the coverage > debugfs file. So this isn't actually a kernel deadlock but syzkaller > misbehaves when that scenario happens. > > Either way, it only fails to mmap with that commit that I've pointed > out.
That info is really helpful here: the proxy file_operations introduced by this commit doesn't have a ->mmap() defined, i.e. it is NULL from the VFS layer's point of view.
The simple reason is that at the time I submitted this series, my Coccinelle script didn't find any debugfs user with a ->mmap() defined. Thus either that script was broken or things have changed in the meanwhile.
I'll look into this tomorrow.
Thank you very much for the effort you put into this!
> > th->cover_fd = open("/sys/kernel/debug/kcov", O_RDWR); > if (th->cover_fd == -1) > fail("open of /sys/kernel/debug/kcov failed"); > if (ioctl(th->cover_fd, KCOV_INIT_TRACE, kCoverSize)) > fail("cover enable write failed"); > th->cover_data = (uintptr_t*)mmap(NULL, kCoverSize * sizeof(th->cover_data[0]), PROT_READ | PROT_WRITE, MAP_SHARED, th->cover_fd, 0); > if ((void*)th->cover_data == MAP_FAILED) > fail("cover mmap failed"); > > And it's the mmap() that fails with -ENODEV.
| |