6.16-stable review patch. If anyone has any objections, please let me know.
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From: Jonas Jelonek jelonek.jonas@gmail.com
commit 06418cb5a1a542a003fdb4ad8e76ea542d57cfba upstream.
Add an explicit check for the xfer length to 'rtl9300_i2c_config_xfer' to ensure the data length isn't within the supported range. In particular a data length of 0 is not supported by the hardware and causes unintended or destructive behaviour.
This limitation becomes obvious when looking at the register documentation [1]. 4 bits are reserved for DATA_WIDTH and the value of these 4 bits is used as N + 1, allowing a data length range of 1 <= len <= 16.
Affected by this is the SMBus Quick Operation which works with a data length of 0. Passing 0 as the length causes an underflow of the value due to:
(len - 1) & 0xf
and effectively specifying a transfer length of 16 via the registers. This causes a 16-byte write operation instead of a Quick Write. For example, on SFP modules without write-protected EEPROM this soft-bricks them by overwriting some initial bytes.
For completeness, also add a quirk for the zero length.
[1] https://svanheule.net/realtek/longan/register/i2c_mst1_ctrl2
Fixes: c366be720235 ("i2c: Add driver for the RTL9300 I2C controller") Cc: stable@vger.kernel.org # v6.13+ Signed-off-by: Jonas Jelonek jelonek.jonas@gmail.com Tested-by: Sven Eckelmann sven@narfation.org Reviewed-by: Chris Packham chris.packham@alliedtelesis.co.nz Tested-by: Chris Packham chris.packham@alliedtelesis.co.nz # On RTL9302C based board Tested-by: Markus Stockhausen markus.stockhausen@gmx.de Signed-off-by: Andi Shyti andi.shyti@kernel.org Link: https://lore.kernel.org/r/20250831100457.3114-3-jelonek.jonas@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/i2c/busses/i2c-rtl9300.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
--- a/drivers/i2c/busses/i2c-rtl9300.c +++ b/drivers/i2c/busses/i2c-rtl9300.c @@ -99,6 +99,9 @@ static int rtl9300_i2c_config_xfer(struc { u32 val, mask;
+ if (len < 1 || len > 16) + return -EINVAL; + val = chan->bus_freq << RTL9300_I2C_MST_CTRL2_SCL_FREQ_OFS; mask = RTL9300_I2C_MST_CTRL2_SCL_FREQ_MASK;
@@ -323,7 +326,7 @@ static const struct i2c_algorithm rtl930 };
static struct i2c_adapter_quirks rtl9300_i2c_quirks = { - .flags = I2C_AQ_NO_CLK_STRETCH, + .flags = I2C_AQ_NO_CLK_STRETCH | I2C_AQ_NO_ZERO_LEN, .max_read_len = 16, .max_write_len = 16, };