[PATCH 1/2] mtd: mtd_[read|write|erase]: check for valid input data

[PATCH 1/2] mtd: mtd_[read|write|erase]: check for valid input data

[Sascha Hauer]

mtd_[read|write|erase] are input functions to the mtd subsystem, so
check for valid input data here rather than relying on the drivers doing
this. The checks are copied from the Kernel as of 4.5-rc5

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 drivers/mtd/core.c      | 22 ++++++++++++++++++++++
 include/linux/mtd/mtd.h |  2 ++
 2 files changed, 24 insertions(+)

diff --git a/drivers/mtd/core.c b/drivers/mtd/core.c
index e35571d..161c6ad 100644
--- a/drivers/mtd/core.c
+++ b/drivers/mtd/core.c
@@ -326,6 +326,11 @@ int mtd_read(struct mtd_info *mtd, loff_t from, size_t len, size_t *retlen,
 	int ret_code;
 	*retlen = 0;
 
+	if (from < 0 || from >= mtd->size || len > mtd->size - from)
+		return -EINVAL;
+	if (!len)
+		return 0;
+
 	/*
 	 * In the absence of an error, drivers return a non-negative integer
 	 * representing the maximum number of bitflips that were corrected on
@@ -344,11 +349,28 @@ int mtd_write(struct mtd_info *mtd, loff_t to, size_t len, size_t *retlen,
 {
 	*retlen = 0;
 
+	if (to < 0 || to >= mtd->size || len > mtd->size - to)
+		return -EINVAL;
+	if (!mtd->write || !(mtd->flags & MTD_WRITEABLE))
+		return -EROFS;
+	if (!len)
+		return 0;
+
 	return mtd->write(mtd, to, len, retlen, buf);
 }
 
 int mtd_erase(struct mtd_info *mtd, struct erase_info *instr)
 {
+	if (instr->addr >= mtd->size || instr->len > mtd->size - instr->addr)
+		return -EINVAL;
+	if (!(mtd->flags & MTD_WRITEABLE))
+		return -EROFS;
+	instr->fail_addr = MTD_FAIL_ADDR_UNKNOWN;
+	if (!instr->len) {
+		instr->state = MTD_ERASE_DONE;
+		mtd_erase_callback(instr);
+		return 0;
+	}
 	return mtd->erase(mtd, instr);
 }
 
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index e430217..421a941 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -26,6 +26,8 @@
 #define MTD_ERASE_DONE          0x08
 #define MTD_ERASE_FAILED        0x10
 
+#define MTD_FAIL_ADDR_UNKNOWN -1LL
+
 /* If the erase fails, fail_addr might indicate exactly which block failed.  If
    fail_addr = 0xffffffff, the failure was not at the device level or was not
    specific to any particular block. */
-- 
2.7.0


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[PATCH 2/2] mtd: nand: default bitflip-reporting threshold to 75% of correction strength

[Sascha Hauer]

Based on Kernel commit 240181fd0ffa6 from Brian Norris:

The MTD API reports -EUCLEAN only if the maximum number of bitflips
found in any ECC block exceeds a certain threshold. This is done to
avoid excessive -EUCLEAN reports to MTD users, which may induce
additional scrubbing of data, even when the ECC algorithm in use is
perfectly capable of handling the bitflips.

This threshold can be controlled by user-space (via sysfs), to allow
users to determine what they are willing to tolerate in their
application. But it still helps to have sane defaults.

In recent discussion [1], it was pointed out that our default threshold
is equal to the correction strength. That means that we won't actually
report any -EUCLEAN (i.e., "bitflips were corrected") errors until there
are almost too many to handle. It was determined that 3/4 of the
correction strength is probably a better default.

[1] http://lists.infradead.org/pipermail/linux-mtd/2015-January/057259.html

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 drivers/mtd/nand/nand_base.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index 554d3d2..ec5a8b7 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -3718,7 +3718,7 @@ int nand_scan_tail(struct mtd_info *mtd)
 	 * properly set.
 	 */
 	if (!mtd->bitflip_threshold)
-		mtd->bitflip_threshold = mtd->ecc_strength;
+		mtd->bitflip_threshold = DIV_ROUND_UP(mtd->ecc_strength * 3, 4);
 
 	/* Check, if we should skip the bad block table scan */
 	if (chip->options & NAND_SKIP_BBTSCAN)
-- 
2.7.0


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