Hi Wolfram,
> On Wed, Nov 15, 2017 at 12:54:09PM -0700, Compostella, Jeremy wrote:
> > On a I2C_SMBUS_I2C_BLOCK_DATA read request, if data->block[0] is
> > greater than I2C_SMBUS_BLOCK_MAX + 1, the underlying I2C driver writes
> greater or equal?
> > data out of the msgbuf1 boundary.
> >
> > It is possible from a user application to run into that issue by call
> > the I2C_SMBUS ioctl with data.block[0] greater than
> > I2C_SMBUS_BLOCK_MAX + 1.
> ditto?
Actually, this is a bit more complicated. Theoretically it should be
"greater than I2C_SMBUS_BLOCK_MAX". The documentation
(Documentation/i2c/dev-interface) says "The block buffers need not be
longer than 32 bytes". However, in practice, The
i2c_smbus_xfer_emulated() function defines:
unsigned char msgbuf1[I2C_SMBUS_BLOCK_MAX+2];
It uses the first element to store the requested length. Therefore,
in practice, we hit the issue with "greater than I2C_SMBUS_BLOCK_MAX +
1".
> Basically good, yet to make the code easier to read I'd suggest
> something like this? Untested, wanted to hear your opinion first.
> drivers/i2c/i2c-core-smbus.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
> diff --git a/drivers/i2c/i2c-core-smbus.c b/drivers/i2c/i2c-core-smbus.c
> index 4bb9927afd0106..5fc5ddd965434f 100644
> --- a/drivers/i2c/i2c-core-smbus.c
> +++ b/drivers/i2c/i2c-core-smbus.c
> @@ -397,16 +397,16 @@ static s32 i2c_smbus_xfer_emulated(struct i2c_adapter *adapter, u16 addr,
> the underlying bus driver */
> break;
> case I2C_SMBUS_I2C_BLOCK_DATA:
> + if (data->block[0] > I2C_SMBUS_BLOCK_MAX) {
> + dev_err(&adapter->dev, "Invalid block size %d\n",
> + data->block[0]);
> + return -EINVAL;
> + }
> +
> if (read_write == I2C_SMBUS_READ) {
> msg[1].len = data->block[0];
> } else {
> msg[0].len = data->block[0] + 1;
> - if (msg[0].len > I2C_SMBUS_BLOCK_MAX + 1) {
> - dev_err(&adapter->dev,
> - "Invalid block write size %d\n",
> - data->block[0]);
> - return -EINVAL;
> - }
> for (i = 1; i <= data->block[0]; i++)
> msgbuf0[i] = data->block[i];
> }
This is a better option, I think I have made such a version at some
points but did not want to touch the other case for some reasons that
I cannot remember now :/
I have a added a little c ternary instruction to keep the same level
of debug/error information. If you don't like it we can remove it.
I have updated, tested and attached the new version to this email. I
also improved the commit message by adding some information about what
is expected by the documentation. I don't know what is the process to
update the patch to the mailing list. Should I send a new email with
the new patch instead ?
Thanks,
Jeremy
>From 72c6683ac2e25304ec01e8fe2974abe744a129a0 Mon Sep 17 00:00:00 2001
From: Jeremy Compostella <jeremy.compostella@xxxxxxxxx>
Date: Wed, 15 Nov 2017 12:31:44 -0700
Subject: [PATCH] i2c: core-smbus: prevent stack corruption on read
I2C_BLOCK_DATA
On a I2C_SMBUS_I2C_BLOCK_DATA read request, if data->block[0] is
greater than I2C_SMBUS_BLOCK_MAX + 1, the underlying I2C driver writes
data out of the msgbuf1 array boundary.
It is possible from a user application to run into that issue by
calling the I2C_SMBUS ioctl with data.block[0] greater than
I2C_SMBUS_BLOCK_MAX + 1.
This patch makes the code compliant with
Documentation/i2c/dev-interface by raising an error when the requested
size is larger than 32 bytes.
Call Trace:
[<ffffffff8139f695>] dump_stack+0x67/0x92
[<ffffffff811802a4>] panic+0xc5/0x1eb
[<ffffffff810ecb5f>] ? vprintk_default+0x1f/0x30
[<ffffffff817456d3>] ? i2cdev_ioctl_smbus+0x303/0x320
[<ffffffff8109a68b>] __stack_chk_fail+0x1b/0x20
[<ffffffff817456d3>] i2cdev_ioctl_smbus+0x303/0x320
[<ffffffff81745aed>] i2cdev_ioctl+0x4d/0x1e0
[<ffffffff811f761a>] do_vfs_ioctl+0x2ba/0x490
[<ffffffff81336e43>] ? security_file_ioctl+0x43/0x60
[<ffffffff811f7869>] SyS_ioctl+0x79/0x90
[<ffffffff81a22e97>] entry_SYSCALL_64_fastpath+0x12/0x6a
Signed-off-by: Jeremy Compostella <jeremy.compostella@xxxxxxxxx>
---
drivers/i2c/i2c-core-smbus.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/drivers/i2c/i2c-core-smbus.c b/drivers/i2c/i2c-core-smbus.c
index 10f00a8..e54a9b8 100644
--- a/drivers/i2c/i2c-core-smbus.c
+++ b/drivers/i2c/i2c-core-smbus.c
@@ -396,16 +396,17 @@ static s32 i2c_smbus_xfer_emulated(struct i2c_adapter *adapter, u16 addr,
the underlying bus driver */
break;
case I2C_SMBUS_I2C_BLOCK_DATA:
+ if (data->block[0] > I2C_SMBUS_BLOCK_MAX) {
+ dev_err(&adapter->dev, "Invalid block %s size %d\n",
+ read_write == I2C_SMBUS_READ ? "read" : "write",
+ data->block[0]);
+ return -EINVAL;
+ }
+
if (read_write == I2C_SMBUS_READ) {
msg[1].len = data->block[0];
} else {
msg[0].len = data->block[0] + 1;
- if (msg[0].len > I2C_SMBUS_BLOCK_MAX + 1) {
- dev_err(&adapter->dev,
- "Invalid block write size %d\n",
- data->block[0]);
- return -EINVAL;
- }
for (i = 1; i <= data->block[0]; i++)
msgbuf0[i] = data->block[i];
}
--
2.9.4
