i2c: smbus: make i2c_smbus_read_block_data() safer

i2c_smbus_read_block_data() is dangerous to use because it may deliver
up to I2C_SMBUS_BLOCK_MAX (32) bytes, which may be surprising to the
caller. Callers tend to allocate buffers of sizes big enough to hold
data from a well-behaving device and do not expect that
i2c_smbus_read_block_data() may attempt to write more data than
expected.

To make i2c_smbus_read_block_data() safer to use, change it so that
it accepts size of the supplied buffer as another argument and ensure
that it will not copy more data than the size of the buffer. Signal
oversized responses with -EMSGSIZE.

To allow users to gradually transition to the new API employ some
macro trickery allowing calling i2c_smbus_read_block_data() with either
3 or 4 arguments. When called with 3 arguments it is assumed that
the buffer size is I2C_SMBUS_BLOCK_MAX bytes. Once everyone is
transitioned to the 4 argument form the macros should be removed.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://patch.msgid.link/ammWUROtUGeriY8G@google.com

0 files changed, 0 insertions, 0 deletions