[PATCH 2/2] mtd: rawnand: ingenic: validate BCH error index in jz4780_correct()

[Guanglei Zhu <zhugl3@xiaopeng.com>]

From: Weibin Liu <liuwb@xiaopeng.com>

The JZ4780 BCH controller reports each corrected bit error as a byte
pair index, in the INDEX field of the BCH_BHERR registers. The field
is 11 bits wide, but nothing in jz4780_correct() checks the reported
index against the size of the data buffer being corrected:

    buf[(index * 2) + 0] ^= mask;
    buf[(index * 2) + 1] ^= mask >> 8;

With data or ECC coming from an untrusted flash, the decoder can
report an index that points past the end of the data buffer, and the
above statements then flip bits outside the buffer.

Reject the page with -EBADMSG when the reported index does not fit in
the data area.

Fixes: ae02ab00aa3c ("mtd: nand: jz4780: driver for NAND devices on JZ4780 SoCs")
Signed-off-by: Weibin Liu <liuwb@xiaopeng.com>
---

Verified with a userspace replica of the correction loop: with
params->size = 512, an index of 256 (first parity word) or at the
field maximum (0x7ff) flips bits past the data buffer (ASAN
heap-buffer-overflow); in-range indices keep correcting as before.

 drivers/mtd/nand/raw/ingenic/jz4780_bch.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/mtd/nand/raw/ingenic/jz4780_bch.c b/drivers/mtd/nand/raw/ingenic/jz4780_bch.c
index 12b5b0484fe9..204bc853c1b4 100644
--- a/drivers/mtd/nand/raw/ingenic/jz4780_bch.c
+++ b/drivers/mtd/nand/raw/ingenic/jz4780_bch.c
@@ -216,6 +216,11 @@ static int jz4780_correct(struct ingenic_ecc *bch,
 						BCH_BHERR_MASK_SHIFT;
 			index = (reg & BCH_BHERR_INDEX_MASK) >>
 						BCH_BHERR_INDEX_SHIFT;
+			if ((index * 2) + 1 >= params->size) {
+				ret = -EBADMSG;
+				goto out;
+			}
+
 			buf[(index * 2) + 0] ^= mask;
 			buf[(index * 2) + 1] ^= mask >> 8;
 		}
-- 
2.50.1