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

[Linux-MTD Mailing List]

Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=144f4c98399e2c0ca60eb414c15a2c68125c18b8
Commit:     144f4c98399e2c0ca60eb414c15a2c68125c18b8
Parent:     0a526341fee054c1e2b9f0e4b2b424ae81707d4c
Author:     Hector Palacios <hector.palacios at digi.com>
AuthorDate: Mon Jul 18 10:39:18 2016 +0200
Committer:  Brian Norris <computersforpeace at gmail.com>
CommitDate: Tue Jul 19 12:54:14 2016 -0700

    mtd: nand: fix bug writing 1 byte less than page size
    
    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")]
    
    Fixes: 29072b96078f ("[MTD] NAND: add subpage write support")
    Signed-off-by: Hector Palacios <hector.palacios at digi.com>
    Acked-by: Boris Brezillon <boris.brezillon at free-electrons.com>
    Cc: <stable at vger.kernel.org>
    Signed-off-by: Brian Norris <computersforpeace at gmail.com>
---
 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 0b0dc29..77533f7 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -2610,7 +2610,7 @@ static int nand_do_write_ops(struct mtd_info *mtd, loff_t to,
 		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;