On Tue, 21 Jun 2022 at 13:22, Geert Uytterhoeven
<geert+renesas@xxxxxxxxx> wrote:
>
> The recent change to split reads into chunks has several problems:
> 1. If an SPI controller has no transfer size limit, max_chunk is
> SIZE_MAX, and num_msgs becomes zero, causing no data to be read
> into the buffer, and exposing the original contents of the buffer
> to userspace,
> 2. If the requested read size is not a multiple of the maximum
> transfer size, the last transfer reads too much data, overflowing
> the buffer,
> 3. The loop logic differs from the write case.
>
> Fix the above by:
> 1. Keeping track of the number of bytes that are still to be
> transferred, instead of precalculating the number of messages and
> keeping track of the number of bytes tranfered,
sp: transferred
> 2. Calculating the transfer size of each individual message, taking
> into account the number of bytes left,
> 3. Switching from a "while"-loop to a "do-while"-loop, and renaming
> "msg_count" to "segment".
>
> While at it, drop the superfluous cast from "unsigned int" to "unsigned
> int", also from at25_ee_write(), where it was probably copied from.
>
> Fixes: 0a35780c755ccec0 ("eeprom: at25: Split reads into chunks and cap write size")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
Thanks Geert for the patch. This is particularly important as I
noticed the "fix" has been backported to stable trees.
I was surprised that patch went in as-is; I thought it needed some
discussion before merging. I wasn't sure if it was the correct fix at
all; I wondered if it should have been fixed at the spi layer. Do you
have an opinion there?
Eddie, can you jump in for some testing and a review of this one?
Cheers,
Joel
> ---
> Tested on Ebisu-4D with 25LC040 EEPROM.
> ---
> drivers/misc/eeprom/at25.c | 26 ++++++++++++--------------
> 1 file changed, 12 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/misc/eeprom/at25.c b/drivers/misc/eeprom/at25.c
> index c9c56fd194c1301f..bdffc6543f6f8b7f 100644
> --- a/drivers/misc/eeprom/at25.c
> +++ b/drivers/misc/eeprom/at25.c
> @@ -80,10 +80,9 @@ static int at25_ee_read(void *priv, unsigned int offset,
> struct at25_data *at25 = priv;
> char *buf = val;
> size_t max_chunk = spi_max_transfer_size(at25->spi);
> - size_t num_msgs = DIV_ROUND_UP(count, max_chunk);
> - size_t nr_bytes = 0;
> - unsigned int msg_offset;
> - size_t msg_count;
> + unsigned int msg_offset = offset;
> + size_t bytes_left = count;
> + size_t segment;
> u8 *cp;
> ssize_t status;
> struct spi_transfer t[2];
> @@ -97,9 +96,8 @@ static int at25_ee_read(void *priv, unsigned int offset,
> if (unlikely(!count))
> return -EINVAL;
>
> - msg_offset = (unsigned int)offset;
> - msg_count = min(count, max_chunk);
> - while (num_msgs) {
> + do {
> + segment = min(bytes_left, max_chunk);
> cp = at25->command;
>
> instr = AT25_READ;
> @@ -131,8 +129,8 @@ static int at25_ee_read(void *priv, unsigned int offset,
> t[0].len = at25->addrlen + 1;
> spi_message_add_tail(&t[0], &m);
>
> - t[1].rx_buf = buf + nr_bytes;
> - t[1].len = msg_count;
> + t[1].rx_buf = buf;
> + t[1].len = segment;
> spi_message_add_tail(&t[1], &m);
>
> status = spi_sync(at25->spi, &m);
> @@ -142,10 +140,10 @@ static int at25_ee_read(void *priv, unsigned int offset,
> if (status)
> return status;
>
> - --num_msgs;
> - msg_offset += msg_count;
> - nr_bytes += msg_count;
> - }
> + msg_offset += segment;
> + buf += segment;
> + bytes_left -= segment;
> + } while (bytes_left > 0);
>
> dev_dbg(&at25->spi->dev, "read %zu bytes at %d\n",
> count, offset);
> @@ -229,7 +227,7 @@ static int at25_ee_write(void *priv, unsigned int off, void *val, size_t count)
> do {
> unsigned long timeout, retries;
> unsigned segment;
> - unsigned offset = (unsigned) off;
> + unsigned offset = off;
> u8 *cp = bounce;
> int sr;
> u8 instr;
> --
> 2.25.1
>
