The patch titled
Subject: android: binder: fix lockdep check on clearing vma
has been added to the -mm mm-unstable branch. Its filename is
android-binder-fix-lockdep-check-on-clearing-vma.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/android-binder-fix-lockdep-check-on-clearing-vma.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Liam Howlett <liam.howlett@xxxxxxxxxx>
Subject: android: binder: fix lockdep check on clearing vma
Date: Mon, 27 Jun 2022 15:18:59 +0000
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@xxxxxxxxxx
Fixes: 472a68df605b ("android: binder: stop saving a pointer to the VMA")
Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Reported-by: syzbot+da54fa8d793ca89c741f@xxxxxxxxxxxxxxxxxxxxxxxxx
Acked-by: Todd Kjos <tkjos@xxxxxxxxxx>
Cc: "Arve Hjønnevåg" <arve@xxxxxxxxxxx>
Cc: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Hridya Valsaraju <hridya@xxxxxxxxxx>
Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
Cc: Martijn Coenen <maco@xxxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/android/binder_alloc.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
--- a/drivers/android/binder_alloc.c~android-binder-fix-lockdep-check-on-clearing-vma
+++ a/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;
}
_
Patches currently in -mm which might be from liam.howlett@xxxxxxxxxx are
android-binder-fix-lockdep-check-on-clearing-vma.patch
maple-tree-add-new-data-structure-fix.patch
lib-test_maple_tree-add-testing-for-maple-tree-fix.patch
mm-mlock-drop-dead-code-in-count_mm_mlocked_page_nr.patch
