| Message ID | b1f0e06c-1f66-2f31-fdad-95c2e50eeddf@I-love.SAKURA.ne.jp (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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@I-love.SAKURA.ne.jp> > 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...
On Thu, May 10, 2018 at 10:07 PM, Al Viro <viro@zeniv.linux.org.uk> wrote: > 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@I-love.SAKURA.ne.jp> >> 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... Need to call d_invalidate() instead of d_drop() in there. Is that what you are referring to? Thanks, Miklos
Miklos Szeredi wrote: > On Thu, May 10, 2018 at 10:07 PM, Al Viro <viro@zeniv.linux.org.uk> wrote: > > 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@I-love.SAKURA.ne.jp> > >> 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... > > Need to call d_invalidate() instead of d_drop() in there. Is that > what you are referring to? > > Thanks, > Miklos > I couldn't catch what Al is worrying about. I assumed that dput() is fine because proc_setup_thread_self() in fs/proc/thread_self.c is doing dput() when new_inode_pseudo() failed after d_alloc_name().
On Fri, May 11, 2018 at 09:55:00AM +0200, Miklos Szeredi wrote: > On Thu, May 10, 2018 at 10:07 PM, Al Viro <viro@zeniv.linux.org.uk> wrote: > > 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@I-love.SAKURA.ne.jp> > >> 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... > > Need to call d_invalidate() instead of d_drop() in there. Is that > what you are referring to? Yes, and do that once on the entire subdirectory...
diff --git a/fs/fuse/control.c b/fs/fuse/control.c index b9ea99c..a651f8e 100644 --- a/fs/fuse/control.c +++ b/fs/fuse/control.c @@ -211,10 +211,12 @@ static struct dentry *fuse_ctl_add_dentry(struct dentry *parent, if (!dentry) return NULL; - fc->ctl_dentry[fc->ctl_ndents++] = dentry; inode = new_inode(fuse_control_sb); - if (!inode) + if (!inode) { + dput(dentry); return NULL; + } + fc->ctl_dentry[fc->ctl_ndents++] = dentry; inode->i_ino = get_next_ino(); inode->i_mode = mode;