68 lines
2.2 KiB
Diff
68 lines
2.2 KiB
Diff
From: Todd Kjos <tkjos@android.com>
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Date: Fri, 1 Mar 2019 15:06:06 -0800
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Subject: binder: fix race between munmap() and direct reclaim
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Origin: https://git.kernel.org/linus/5cec2d2e5839f9c0fec319c523a911e0a7fd299f
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Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2019-1999
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An munmap() on a binder device causes binder_vma_close() to be called
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which clears the alloc->vma pointer.
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If direct reclaim causes binder_alloc_free_page() to be called, there
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is a race where alloc->vma is read into a local vma pointer and then
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used later after the mm->mmap_sem is acquired. This can result in
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calling zap_page_range() with an invalid vma which manifests as a
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use-after-free in zap_page_range().
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The fix is to check alloc->vma after acquiring the mmap_sem (which we
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were acquiring anyway) and skip zap_page_range() if it has changed
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to NULL.
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Signed-off-by: Todd Kjos <tkjos@google.com>
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Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
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Cc: stable <stable@vger.kernel.org>
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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---
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drivers/android/binder_alloc.c | 17 ++++++++---------
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1 file changed, 8 insertions(+), 9 deletions(-)
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diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
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index 030c98f35cca..3863ef78e40f 100644
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--- a/drivers/android/binder_alloc.c
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+++ b/drivers/android/binder_alloc.c
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@@ -958,14 +958,13 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
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index = page - alloc->pages;
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page_addr = (uintptr_t)alloc->buffer + index * PAGE_SIZE;
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+
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+ mm = alloc->vma_vm_mm;
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+ if (!mmget_not_zero(mm))
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+ goto err_mmget;
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+ if (!down_write_trylock(&mm->mmap_sem))
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+ goto err_down_write_mmap_sem_failed;
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vma = binder_alloc_get_vma(alloc);
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- if (vma) {
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- if (!mmget_not_zero(alloc->vma_vm_mm))
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- goto err_mmget;
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- mm = alloc->vma_vm_mm;
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- if (!down_write_trylock(&mm->mmap_sem))
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- goto err_down_write_mmap_sem_failed;
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- }
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list_lru_isolate(lru, item);
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spin_unlock(lock);
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@@ -979,9 +978,9 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
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trace_binder_unmap_user_end(alloc, index);
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- up_write(&mm->mmap_sem);
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- mmput(mm);
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}
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+ up_write(&mm->mmap_sem);
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+ mmput(mm);
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trace_binder_unmap_kernel_start(alloc, index);
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--
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2.20.1
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