Re: [PATCH v5 1/4] btrfs: extent_io: do extra check for extent buffer read write functions

On Thu, Aug 20, 2020 at 07:14:13AM +0800, Qu Wenruo wrote:

quoted

quoted

+static inline int check_eb_range(const struct extent_buffer *eb,
+				 unsigned long start, unsigned long len)
+{
+	/* start, start + len should not go beyond eb->len nor overflow */
+	if (unlikely(start > eb->len || start + len > eb->len ||
+		     len > eb->len)) {

Can the number of condition be reduced? If 'start + len' overflows, then
we don't need to check 'start > eb->len', and for the case where
start = 1024 and len = -1024 the 'len > eb-len' would be enough.

I'm afraid not.
Although 'start > eb->len || len > eb->len' is enough to detect overflow
case, it no longer detects cases like 'start = 2k, len = 3k' while
eb->len == 4K case.

So we still need all 3 checks.

I was suggesting 'start + len > eb->len', not 'start > eb-len'.

"start > eb->len" is implied by "start + len > eb->len".