linux-kernel - [PATCH 5.15 71/73] android: binder: fix lockdep check on clearing vma

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Message-Id: <20220902121406.747072796@linuxfoundation.org>
Date:   Fri,  2 Sep 2022 14:19:35 +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,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        syzbot+da54fa8d793ca89c741f@...kaller.appspotmail.com,
        Todd Kjos <tkjos@...gle.com>,
        Arve Hjønnevåg <arve@...roid.com>,
        "Christian Brauner (Microsoft)" <brauner@...nel.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Martijn Coenen <maco@...roid.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 5.15 71/73] android: binder: fix lockdep check on clearing vma

From: Liam Howlett <liam.howlett@...cle.com>

commit b0cab80ecd54ae3b2356bb081af0bffd538c8265 upstream.

When munmapping a vma, the mmap_lock can be degraded to a write before
calling close() on the file handle.  The binder close() function calls
binder_alloc_set_vma() to clear the vma address, which now has a lock dep
check for writing on the mmap_lock.  Change the lockdep check to ensure
the reading lock is held while clearing and keep the write check while
writing.

Link: https://lkml.kernel.org/r/20220627151857.2316964-1-Liam.Howlett@oracle.com
Fixes: 472a68df605b ("android: binder: stop saving a pointer to the VMA")
Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
Reported-by: syzbot+da54fa8d793ca89c741f@...kaller.appspotmail.com
Acked-by: Todd Kjos <tkjos@...gle.com>
Cc: "Arve Hjønnevåg" <arve@...roid.com>
Cc: Christian Brauner (Microsoft) <brauner@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Hridya Valsaraju <hridya@...gle.com>
Cc: Joel Fernandes <joel@...lfernandes.org>
Cc: Martijn Coenen <maco@...roid.com>
Cc: Suren Baghdasaryan <surenb@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/android/binder_alloc.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -315,12 +315,19 @@ static inline void binder_alloc_set_vma(
 {
 	unsigned long vm_start = 0;
 
+	/*
+	 * Allow clearing the vma with holding just the read lock to allow
+	 * munmapping downgrade of the write lock before freeing and closing the
+	 * file using binder_alloc_vma_close().
+	 */
 	if (vma) {
 		vm_start = vma->vm_start;
 		alloc->vma_vm_mm = vma->vm_mm;
+		mmap_assert_write_locked(alloc->vma_vm_mm);
+	} else {
+		mmap_assert_locked(alloc->vma_vm_mm);
 	}
 
-	mmap_assert_write_locked(alloc->vma_vm_mm);
 	alloc->vma_addr = vm_start;
 }