binder: fix race between munmap() and direct reclaim (CVE-2019-1999)

debian/changelog

@@ -16,6 +16,7 @@ linux (4.19.37-6) UNRELEASED; urgency=medium
   * [powerpc*] mm/64s/hash: Reallocate context ids on fork (CVE-2019-12817)
   * nfc: Ensure presence of required attributes in the deactivate_target handler
     (CVE-2019-12984)
+  * binder: fix race between munmap() and direct reclaim (CVE-2019-1999)
 
  -- Salvatore Bonaccorso <carnil@debian.org>  Sun, 23 Jun 2019 16:15:17 +0200
 

debian/patches/bugfix/all/binder-fix-race-between-munmap-and-direct-reclaim.patch

@@ -0,0 +1,68 @@
+From 37b68ba30a93ee10b2e0531affdab9665dbe7b80 Mon Sep 17 00:00:00 2001
+From: Todd Kjos <tkjos@android.com>
+Date: Fri, 1 Mar 2019 15:06:06 -0800
+Subject: [PATCH] binder: fix race between munmap() and direct reclaim
+Origin: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/patch/?id=5cec2d2e5839f9c0fec319c523a911e0a7fd299f
+Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2019-1999
+
+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>
+---
+ drivers/android/binder_alloc.c | 17 ++++++++---------
+ 1 file changed, 8 insertions(+), 9 deletions(-)
+
+diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
+index 030c98f35cca..3863ef78e40f 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);
+@@ -979,9 +978,9 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
+ 
+ 		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);
+ 
+-- 
+2.20.1
+

debian/patches/series

@@ -233,6 +233,7 @@ bugfix/all/ptrace-Fix-ptracer_cred-handling-for-PTRACE_TRACEME.patch
 bugfix/x86/x86-insn-eval-Fix-use-after-free-access-to-LDT-entry.patch
 bugfix/powerpc/powerpc-mm-64s-hash-Reallocate-context-ids-on-fork.patch
 bugfix/all/nfc-Ensure-presence-of-required-attributes-in-the-deactivate_target.patch
+bugfix/all/binder-fix-race-between-munmap-and-direct-reclaim.patch
 
 # Fix exported symbol versions
 bugfix/all/module-disable-matching-missing-version-crc.patch