On Tue, Jul 17, 2018 at 5:46 AM Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > On Tue, Jul 17, 2018 at 1:36 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > > On Tue, Jul 17, 2018 at 1:14 PM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > >> On Thu, Jul 12, 2018 at 5:49 PM, syzbot > >> <syzbot+3f7b29af1baa9d0a55be@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > >>> Hello, > >>> > >>> syzbot found the following crash on: > >>> > >>> HEAD commit: c25c74b7476e Merge tag 'trace-v4.18-rc3-2' of git://git.ke.. > >>> git tree: upstream > >>> console output: https://syzkaller.appspot.com/x/log.txt?x=177bcec2400000 > >>> kernel config: https://syzkaller.appspot.com/x/.config?x=25856fac4e580aa7 > >>> dashboard link: https://syzkaller.appspot.com/bug?extid=3f7b29af1baa9d0a55be > >>> compiler: gcc (GCC) 8.0.1 20180413 (experimental) > >>> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=13aa7678400000 > >>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17492678400000 > >>> > >>> IMPORTANT: if you fix the bug, please add the following tag to the commit: > >>> Reported-by: syzbot+3f7b29af1baa9d0a55be@xxxxxxxxxxxxxxxxxxxxxxxxx > >>> > >>> random: sshd: uninitialized urandom read (32 bytes read) > >>> random: sshd: uninitialized urandom read (32 bytes read) > >>> random: sshd: uninitialized urandom read (32 bytes read) > >>> > >>> ================================================ > >>> WARNING: lock held when returning to user space! > >>> 4.18.0-rc4+ #143 Not tainted > >>> ------------------------------------------------ > >>> syz-executor012/4539 is leaving the kernel with locks still held! > >>> 1 lock held by syz-executor012/4539: > >>> #0: (____ptrval____) (&fi->mutex){+.+.}, at: fuse_lock_inode+0xaf/0xe0 > >>> fs/fuse/inode.c:363 > >> > >> False positive. > >> > >> fi->mutex is definitely not held by the acquiring task when returning > >> to userspace. Maybe syzkaller is confused by the fact that there are > >> several interdependent tasks involved with fuse: the one calling into > >> fuse by doing something (looking up ./file0/file0) and the one that > >> reads the fuse device (returning with the LOOKUP request for "file0"). > >> The second one will return with that lock held, but it's not the one > >> that acquired it, so there's no bug at all here. > > > > Hi Miklos, > > > > syzkaller is unrelated here. That's what kernel self-detects and > > prints. So either way there is something to fix in kernel here: either > > fuse or lockdep. > > > > +Alistair did some analysis offline, hope you don't mind if I repost > > your description: > > === > > Just from reading the code, I think I can see how this happens. Fuse > > is wrapping its inode mutex with a check for "parallel_dirops", which > > is set up in process_init_reply(). The FUSE_PARALLEL_DIROPS appears to > > always be set, in fuse_send_init(), but its initial state is to be > > disabled. So if the mutex gets taken, and it'll never be unlocked if > > the initial command is flushed by fuse_readdir()'s use of > > fuse_lock_inode(). > > === > > Ah, indeed. Fix attached. Looks good to me. Tested-by: Alistair Strachan <astrachan@xxxxxxxxxx> > Thanks, > Miklos
