Message ID | 1555571261-7298-2-git-send-email-tyhicks@canonical.com |
---|---|
State | New |
Headers | show |
Series | [1/1] binder: fix race between munmap() and direct reclaim | expand |
On 18.04.19 09:07, Tyler Hicks wrote: > From: Todd Kjos <tkjos@android.com> > > An munmap() on a binder device causes binder_vma_close() to be called > which clears the alloc->vma pointer. > > If direct reclaim causes binder_alloc_free_page() to be called, there > is a race where alloc->vma is read into a local vma pointer and then > used later after the mm->mmap_sem is acquired. This can result in > calling zap_page_range() with an invalid vma which manifests as a > use-after-free in zap_page_range(). > > The fix is to check alloc->vma after acquiring the mmap_sem (which we > were acquiring anyway) and skip zap_page_range() if it has changed > to NULL. > > Signed-off-by: Todd Kjos <tkjos@google.com> > Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> > Cc: stable <stable@vger.kernel.org> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > > CVE-2019-1999 > > (backported from commit 5cec2d2e5839f9c0fec319c523a911e0a7fd299f) > [tyhicks: Backport to 5.0: > - The write mode of mmap_sem is held in 5.0] > Signed-off-by: Tyler Hicks <tyhicks@canonical.com> Acked-by: Stefan Bader <stefan.bader@canonical.com> > --- > drivers/android/binder_alloc.c | 18 ++++++++---------- > 1 file changed, 8 insertions(+), 10 deletions(-) > > diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c > index 6a9a4b83b057..c4d8b786d671 100644 > --- a/drivers/android/binder_alloc.c > +++ b/drivers/android/binder_alloc.c > @@ -958,14 +958,13 @@ enum lru_status binder_alloc_free_page(struct list_head *item, > > index = page - alloc->pages; > page_addr = (uintptr_t)alloc->buffer + index * PAGE_SIZE; > + > + mm = alloc->vma_vm_mm; > + if (!mmget_not_zero(mm)) > + goto err_mmget; > + if (!down_write_trylock(&mm->mmap_sem)) > + goto err_down_write_mmap_sem_failed; > vma = binder_alloc_get_vma(alloc); > - if (vma) { > - if (!mmget_not_zero(alloc->vma_vm_mm)) > - goto err_mmget; > - mm = alloc->vma_vm_mm; > - if (!down_write_trylock(&mm->mmap_sem)) > - goto err_down_write_mmap_sem_failed; > - } > > list_lru_isolate(lru, item); > spin_unlock(lock); > @@ -978,10 +977,9 @@ enum lru_status binder_alloc_free_page(struct list_head *item, > PAGE_SIZE); > > trace_binder_unmap_user_end(alloc, index); > - > - up_write(&mm->mmap_sem); > - mmput(mm); > } > + up_write(&mm->mmap_sem); > + mmput(mm); > > trace_binder_unmap_kernel_start(alloc, index); > >
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c index 6a9a4b83b057..c4d8b786d671 100644 --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -958,14 +958,13 @@ enum lru_status binder_alloc_free_page(struct list_head *item, index = page - alloc->pages; page_addr = (uintptr_t)alloc->buffer + index * PAGE_SIZE; + + mm = alloc->vma_vm_mm; + if (!mmget_not_zero(mm)) + goto err_mmget; + if (!down_write_trylock(&mm->mmap_sem)) + goto err_down_write_mmap_sem_failed; vma = binder_alloc_get_vma(alloc); - if (vma) { - if (!mmget_not_zero(alloc->vma_vm_mm)) - goto err_mmget; - mm = alloc->vma_vm_mm; - if (!down_write_trylock(&mm->mmap_sem)) - goto err_down_write_mmap_sem_failed; - } list_lru_isolate(lru, item); spin_unlock(lock); @@ -978,10 +977,9 @@ enum lru_status binder_alloc_free_page(struct list_head *item, PAGE_SIZE); trace_binder_unmap_user_end(alloc, index); - - up_write(&mm->mmap_sem); - mmput(mm); } + up_write(&mm->mmap_sem); + mmput(mm); trace_binder_unmap_kernel_start(alloc, index);