[PATCH 4.19 064/118] nvmem: core: fix read buffer in place

[Greg Kroah-Hartman]

[ Upstream commit 2fe518fecb3a4727393be286db9804cd82ee2d91 ]

When the bit_offset in the cell is zero, the pointer to the msb will
not be properly initialized (ie, will still be pointing to the first
byte in the buffer).

This being the case, if there are bits to clear in the msb, those will
be left untouched while the mask will incorrectly clear bit positions
on the first byte.

This commit also makes sure that any byte unused in the cell is
cleared.

Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@xxxxxxxxxx>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/nvmem/core.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 7c530c88b3fb..99de51e87f7f 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -1028,7 +1028,7 @@ EXPORT_SYMBOL_GPL(nvmem_cell_put);
 static void nvmem_shift_read_buffer_in_place(struct nvmem_cell *cell, void *buf)
 {
 	u8 *p, *b;
-	int i, bit_offset = cell->bit_offset;
+	int i, extra, bit_offset = cell->bit_offset;
 
 	p = b = buf;
 	if (bit_offset) {
@@ -1043,11 +1043,16 @@ static void nvmem_shift_read_buffer_in_place(struct nvmem_cell *cell, void *buf)
 			p = b;
 			*b++ >>= bit_offset;
 		}
-
-		/* result fits in less bytes */
-		if (cell->bytes != DIV_ROUND_UP(cell->nbits, BITS_PER_BYTE))
-			*p-- = 0;
+	} else {
+		/* point to the msb */
+		p += cell->bytes - 1;
 	}
+
+	/* result fits in less bytes */
+	extra = cell->bytes - DIV_ROUND_UP(cell->nbits, BITS_PER_BYTE);
+	while (--extra >= 0)
+		*p-- = 0;
+
 	/* clear msb bits if any leftover in the last byte */
 	*p &= GENMASK((cell->nbits%BITS_PER_BYTE) - 1, 0);
 }
-- 
2.20.1