[PATCH] mtd: mtdram: check offs and len in mtdram->erase

[Sudip Mukherjee <sudipm.mukherjee@gmail.com>]

We should prevent user to erasing mtd device with an unaligned offset
or length.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
---

I am not sure if I should add the Signed-off-by of
Dongsheng Yang <yangds.fnst@cn.fujitsu.com> . He is the original author
and he should get the credit for that.

 drivers/mtd/devices/mtdram.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/drivers/mtd/devices/mtdram.c b/drivers/mtd/devices/mtdram.c
index 8e28508..21b6a05 100644
--- a/drivers/mtd/devices/mtdram.c
+++ b/drivers/mtd/devices/mtdram.c
@@ -32,8 +32,35 @@ MODULE_PARM_DESC(erase_size, "Device erase block size in KiB");
 // We could store these in the mtd structure, but we only support 1 device..
 static struct mtd_info *mtd_info;
 
+static int check_offs_len(struct mtd_info *mtd, loff_t ofs, uint64_t len)
+{
+	int ret = 0;
+	uint64_t temp_len, rem;
+
+	/* Start address must align on block boundary */
+	temp_len = ofs;
+	rem = do_div(temp_len, mtd->erasesize);
+	if (rem) {
+		pr_debug("%s: unaligned address\n", __func__);
+		ret = -EINVAL;
+	}
+
+	/* Length must align on block boundary */
+	temp_len = len;
+	rem = do_div(temp_len, mtd->erasesize);
+
+	if (rem) {
+		pr_debug("%s: length not block aligned\n", __func__);
+		ret = -EINVAL;
+	}
+
+	return ret;
+}
+
 static int ram_erase(struct mtd_info *mtd, struct erase_info *instr)
 {
+	if (check_offs_len(mtd, instr->addr, instr->len))
+		return -EINVAL;
 	memset((char *)mtd->priv + instr->addr, 0xff, instr->len);
 	instr->state = MTD_ERASE_DONE;
 	mtd_erase_callback(instr);
-- 
1.9.1