| Message ID | 7ae260778d2c08986348ea48ce02ef148100e088.1655817534.git.geert+renesas@glider.be (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 19e506b317497a8c2b3ec2f12314d355d2f00ad0 |
| Headers | show |
| Series | eeprom: at25: Rework buggy read splitting | expand |
On Tue, 21 Jun 2022 at 13:22, Geert Uytterhoeven <geert+renesas@glider.be> 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@glider.be> 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 >
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;
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, 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@glider.be> --- Tested on Ebisu-4D with 25LC040 EEPROM. --- drivers/misc/eeprom/at25.c | 26 ++++++++++++-------------- 1 file changed, 12 insertions(+), 14 deletions(-)