Patch "mtd: nand: fix bug writing 1 byte less than page size" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

mtd: nand: fix bug writing 1 byte less than page size

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mtd-nand-fix-bug-writing-1-byte-less-than-page-size.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Hector Palacios <[email protected]>
Date: Mon, 18 Jul 2016 10:39:18 +0200
Subject: mtd: nand: fix bug writing 1 byte less than page size

From: Hector Palacios <[email protected]>

commit 144f4c98399e2c0ca60eb414c15a2c68125c18b8 upstream.

nand_do_write_ops() determines if it is writing a partial page with the formula:

	part_pagewr = (column || writelen < (mtd->writesize - 1))

When 'writelen' is exactly 1 byte less than the NAND page size the formula equates to zero, so the code doesn't process it as a partial write, although it should.
As a consequence the function remains in the while(1) loop with 'writelen' becoming 0xffffffff and iterating endlessly.

The bug may not be easy to reproduce in Linux since user space tools usually force the padding or round-up the write size to a page-size multiple.
This was discovered in U-Boot where the issue can be reproduced by writing any size that is 1 byte less than a page-size multiple. For example, on a NAND with 2K page (0x800):
=> nand erase.part <partition>
=> nand write $loadaddr <partition> 7ff

[Editor's note: the bug was added in commit 29072b96078f, but moved around in commit 66507c7bc8895 ("mtd: nand: Add support to use nand_base poi databuf as bounce buffer")]

---
 drivers/mtd/nand/nand_base.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -2586,7 +2586,7 @@ static int nand_do_write_ops(struct mtd_
 		int cached = writelen > bytes && page != blockmask;
 		uint8_t *wbuf = buf;
 		int use_bufpoi;
-		int part_pagewr = (column || writelen < (mtd->writesize - 1));
+		int part_pagewr = (column || writelen < mtd->writesize);
 
 		if (part_pagewr)
 			use_bufpoi = 1;

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/mtd-nand-fix-bug-writing-1-byte-less-than-page-size.patch