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

[Greg Kroah-Hartman]

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@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # 5.15+
> Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>
> Acked-by: Todd Kjos <tkjos@xxxxxxxxxx>
> Link: https://lore.kernel.org/r/20221104231235.348958-1-cmllamas@xxxxxxxxxx
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> [cmllamas: renamed alloc->mm since missing e66b77e50522]
> Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>
> ---
>  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