i2c-dev: Add support for I2C_M_RECV_LEN
As the bus driver side implementation of I2C_M_RECV_LEN is heavily
tied to SMBus, we can't support received length over 32 bytes, but
let's at least support that.
In practice, the caller will have to setup a buffer large enough to
cover the case where received length byte has value 32, so minimum
32 + 1 = 33 bytes, possibly more if there is a fixed number of bytes
added for the specific slave (for example a checksum.)
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Tested-by: Douglas Gilbert <dgilbert@interlog.com>
diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c
index 4504832..5ec2261 100644
--- a/drivers/i2c/i2c-dev.c
+++ b/drivers/i2c/i2c-dev.c
@@ -265,19 +265,41 @@
res = 0;
for (i = 0; i < rdwr_arg.nmsgs; i++) {
- /* Limit the size of the message to a sane amount;
- * and don't let length change either. */
- if ((rdwr_pa[i].len > 8192) ||
- (rdwr_pa[i].flags & I2C_M_RECV_LEN)) {
+ /* Limit the size of the message to a sane amount */
+ if (rdwr_pa[i].len > 8192) {
res = -EINVAL;
break;
}
+
data_ptrs[i] = (u8 __user *)rdwr_pa[i].buf;
rdwr_pa[i].buf = memdup_user(data_ptrs[i], rdwr_pa[i].len);
if (IS_ERR(rdwr_pa[i].buf)) {
res = PTR_ERR(rdwr_pa[i].buf);
break;
}
+
+ /*
+ * If the message length is received from the slave (similar
+ * to SMBus block read), we must ensure that the buffer will
+ * be large enough to cope with a message length of
+ * I2C_SMBUS_BLOCK_MAX as this is the maximum underlying bus
+ * drivers allow. The first byte in the buffer must be
+ * pre-filled with the number of extra bytes, which must be
+ * at least one to hold the message length, but can be
+ * greater (for example to account for a checksum byte at
+ * the end of the message.)
+ */
+ if (rdwr_pa[i].flags & I2C_M_RECV_LEN) {
+ if (!(rdwr_pa[i].flags & I2C_M_RD) ||
+ rdwr_pa[i].buf[0] < 1 ||
+ rdwr_pa[i].len < rdwr_pa[i].buf[0] +
+ I2C_SMBUS_BLOCK_MAX) {
+ res = -EINVAL;
+ break;
+ }
+
+ rdwr_pa[i].len = rdwr_pa[i].buf[0];
+ }
}
if (res < 0) {
int j;