linux-kernel - [PATCH 5.0 53/89] binder: fix handling of misaligned binder object

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Message-Id: <20190430113612.171167211@linuxfoundation.org>
Date:   Tue, 30 Apr 2019 13:38:44 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Todd Kjos <tkjos@...gle.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        syzbot+55de1eb4975dec156d8f@...kaller.appspotmail.com
Subject: [PATCH 5.0 53/89] binder: fix handling of misaligned binder object

From: Todd Kjos <tkjos@...roid.com>

commit 26528be6720bb40bc8844e97ee73a37e530e9c5e upstream.

Fixes crash found by syzbot:
kernel BUG at drivers/android/binder_alloc.c:LINE! (2)

Reported-and-tested-by: syzbot+55de1eb4975dec156d8f@...kaller.appspotmail.com
Signed-off-by: Todd Kjos <tkjos@...gle.com>
Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>
Cc: stable <stable@...r.kernel.org> # 5.0, 4.19, 4.14
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/android/binder_alloc.c |   18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -959,14 +959,13 @@ enum lru_status binder_alloc_free_page(s
 
 	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);
@@ -979,10 +978,9 @@ enum lru_status binder_alloc_free_page(s
 			       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);