[PATCH v2 1/2] ras: fix an off-by-one error in __find_elem()

[Cong Wang]

ce_arr.array[] is always within the range [0, ce_arr.n-1].
However, the binary search code in __find_elem() uses ce_arr.n
as the maximum index, which could lead to an off-by-one
out-of-bound access right after the while loop. In this case,
we should not even read it, just return -ENOKEY instead.

Note, this could cause a kernel crash if ce_arr.n is exactly
MAX_ELEMS.

Fixes: 011d82611172 ("RAS: Add a Corrected Errors Collector")
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
---
 drivers/ras/cec.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/ras/cec.c b/drivers/ras/cec.c
index 2d9ec378a8bc..a4ff54e50673 100644
--- a/drivers/ras/cec.c
+++ b/drivers/ras/cec.c
@@ -204,10 +204,11 @@ static int __find_elem(struct ce_array *ca, u64 pfn, unsigned int *to)
 	if (to)
 		*to = min;
 
-	this_pfn = PFN(ca->array[min]);
-
-	if (this_pfn == pfn)
-		return min;
+	if (min < ca->n) {
+		this_pfn = PFN(ca->array[min]);
+		if (this_pfn == pfn)
+			return min;
+	}
 
 	return -ENOKEY;
 }
-- 
2.20.1