On Wed, May 09, 2018 at 07:58:58PM +0900, Tetsuo Handa wrote: > >From 9f41081f8bd6762a6f629e5e23e6d07a62bba69c Mon Sep 17 00:00:00 2001 > From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> > Date: Sat, 28 Apr 2018 11:24:09 +0900 > Subject: [PATCH] fuse: don't keep inode-less dentry at fuse_ctl_add_dentry(). > > syzbot is reporting NULL pointer dereference at fuse_ctl_remove_conn() [1]. > Since fc->ctl_ndents is incremented by fuse_ctl_add_conn() when new_inode() > failed, fuse_ctl_remove_conn() reaches an inode-less dentry and tries to > clear d_inode(dentry)->i_private field. Fix this by calling dput() rather > than incrementing fc->ctl_ndents when new_inode() failed. That looks bloody awful. Sure, everything that accesses fc->ctl_dentry is synchronous with this, but it would've been much easier to follow if shoving dentry into that array happened only after it's been fully set up. Incidentally, there's a nasty headache waiting to happen in that code - consider a twit mounting something on that. And think what happens when connection gets shut down...
