Commit 3c597282 authored Jun 19, 2020 by Gao Xiang

erofs: fix partially uninitialized misuse in z_erofs_onlinepage_fixup



Hongyu reported "id != index" in z_erofs_onlinepage_fixup() with
specific aarch64 environment easily, which wasn't shown before.

After digging into that, I found that high 32 bits of page->private
was set to 0xaaaaaaaa rather than 0 (due to z_erofs_onlinepage_init
behavior with specific compiler options). Actually we only use low
32 bits to keep the page information since page->private is only 4
bytes on most 32-bit platforms. However z_erofs_onlinepage_fixup()
uses the upper 32 bits by mistake.

Let's fix it now.

Reported-and-tested-by: Hongyu Jin <hongyu.jin@unisoc.com>
Fixes: 3883a79a ("staging: erofs: introduce VLE decompression support")
Cc: <stable@vger.kernel.org> # 4.19+
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Link: https://lore.kernel.org/r/20200618234349.22553-1-hsiangkao@aol.com


Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

parent b3a9e3b9

fs/erofs/zdata.h

+10 −10

Original line number	Diff line number	Diff line
		@@ -144,22 +144,22 @@ static inline void z_erofs_onlinepage_init(struct page *page)
		static inline void z_erofs_onlinepage_fixup(struct page *page,
		uintptr_t index, bool down)
		{
		unsigned long *p, o, v, id;
		repeat:
		p = &page_private(page);
		o = READ_ONCE(*p);
		union z_erofs_onlinepage_converter u = { .v = &page_private(page) };
		int orig, orig_index, val;

		id = o >> Z_EROFS_ONLINEPAGE_INDEX_SHIFT;
		if (id) {
		repeat:
		orig = atomic_read(u.o);
		orig_index = orig >> Z_EROFS_ONLINEPAGE_INDEX_SHIFT;
		if (orig_index) {
		if (!index)
		return;

		DBG_BUGON(id != index);
		DBG_BUGON(orig_index != index);
		}

		v = (index << Z_EROFS_ONLINEPAGE_INDEX_SHIFT) \|
		((o & Z_EROFS_ONLINEPAGE_COUNT_MASK) + (unsigned int)down);
		if (cmpxchg(p, o, v) != o)
		val = (index << Z_EROFS_ONLINEPAGE_INDEX_SHIFT) \|
		((orig & Z_EROFS_ONLINEPAGE_COUNT_MASK) + (unsigned int)down);
		if (atomic_cmpxchg(u.o, orig, val) != orig)
		goto repeat;
		}

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