[PATCH] w1: ds28e17: reject an oversize length on an I2C block read

[Maoyi Xie]

w1_f19_i2c_master_transfer() is the master_xfer for the DS28E17 1-Wire
to I2C bridge. On an I2C_M_RECV_LEN read, it takes the length from the
device. The downstream slave puts a length byte in buf[0]. The driver
then reads that many bytes into buf[1] with w1_f19_i2c_read().

buf[0] is controlled by the device and can be 0 to 255.
w1_f19_i2c_read() only rejects a zero count. The caller buffer is
I2C_SMBUS_BLOCK_MAX + 2, so 34 bytes. A length above 32 makes the read
run past it, up to about 222 bytes out of bounds.

The SMBus core does check buf[0] against I2C_SMBUS_BLOCK_MAX. That
check runs after master_xfer returns. By then the write is already
done. i2c-algo-bit rejects an oversize length before it copies, and
returns -EPROTO.

Reject a length above I2C_SMBUS_BLOCK_MAX at both RECV_LEN sites, the
same way i2c-algo-bit does.

Fixes: ebc4768ac497 ("add w1_ds28e17 driver for the DS28E17 Onewire to I2C master bridge")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Maoyi Xie <maoyixie.tju@xxxxxxxxx>
---
 drivers/w1/slaves/w1_ds28e17.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/w1/slaves/w1_ds28e17.c b/drivers/w1/slaves/w1_ds28e17.c
index e53bc41bde3ca..b638963d4b595 100644
--- a/drivers/w1/slaves/w1_ds28e17.c
+++ b/drivers/w1/slaves/w1_ds28e17.c
@@ -389,6 +389,10 @@ static int w1_f19_i2c_master_transfer(struct i2c_adapter *adapter,
 			 * another simple read in that case.
 			 */
 			if (msgs[i+1].flags & I2C_M_RECV_LEN) {
+				if (msgs[i+1].buf[0] > I2C_SMBUS_BLOCK_MAX) {
+					i = -EPROTO;
+					goto error;
+				}
 				result = w1_f19_i2c_read(sl, msgs[i+1].addr,
 					&(msgs[i+1].buf[1]), msgs[i+1].buf[0]);
 				if (result < 0) {
@@ -415,6 +419,10 @@ static int w1_f19_i2c_master_transfer(struct i2c_adapter *adapter,
 			 * another simple read in that case.
 			 */
 			if (msgs[i].flags & I2C_M_RECV_LEN) {
+				if (msgs[i].buf[0] > I2C_SMBUS_BLOCK_MAX) {
+					i = -EPROTO;
+					goto error;
+				}
 				result = w1_f19_i2c_read(sl,
 					msgs[i].addr,
 					&(msgs[i].buf[1]),
-- 
2.34.1