Re: [PATCH 6.0] binder: validate alloc->mm in ->mmap() handler

[Carlos Llamas <cmllamas@google.com>]

On Wed, Nov 30, 2022 at 01:40:40PM +0100, Greg Kroah-Hartman wrote:
> On Wed, Nov 23, 2022 at 06:08:09PM +0000, Carlos Llamas wrote:
> > commit 3ce00bb7e91cf57d723905371507af57182c37ef upstream.
> > 
> > Since commit 1da52815d5f1 ("binder: fix alloc->vma_vm_mm null-ptr
> > dereference") binder caches a pointer to the current->mm during open().
> > This fixes a null-ptr dereference reported by syzkaller. Unfortunately,
> > it also opens the door for a process to update its mm after the open(),
> > (e.g. via execve) making the cached alloc->mm pointer invalid.
> > 
> > Things get worse when the process continues to mmap() a vma. From this
> > point forward, binder will attempt to find this vma using an obsolete
> > alloc->mm reference. Such as in binder_update_page_range(), where the
> > wrong vma is obtained via vma_lookup(), yet binder proceeds to happily
> > insert new pages into it.
> > 
> > To avoid this issue fail the ->mmap() callback if we detect a mismatch
> > between the vma->vm_mm and the original alloc->mm pointer. This prevents
> > alloc->vm_addr from getting set, so that any subsequent vma_lookup()
> > calls fail as expected.
> > 
> > Fixes: 1da52815d5f1 ("binder: fix alloc->vma_vm_mm null-ptr dereference")
> > Reported-by: Jann Horn <jannh@google.com>
> > Cc: <stable@vger.kernel.org> # 5.15+
> > Signed-off-by: Carlos Llamas <cmllamas@google.com>
> > Acked-by: Todd Kjos <tkjos@google.com>
> > Link: https://lore.kernel.org/r/20221104231235.348958-1-cmllamas@google.com
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > [cmllamas: renamed alloc->mm since missing e66b77e50522]
> > Signed-off-by: Carlos Llamas <cmllamas@google.com>
> > ---
> >  drivers/android/binder_alloc.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> 
> This is already in the 6.0 queue, is this a different version?
> 
> thanks,
> 
> greg k-h

Oh, please ignore this. It seems Sasha backported the change correctly.