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SubjectRE: [PATCH] ipmi: ipmb: don't allocate i2c_client on stack
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Hi Arnd,

LGTM.

-----Original Message-----
From: Arnd Bergmann <arnd@arndb.de>
Sent: Wednesday, June 19, 2019 8:51 AM
To: Corey Minyard <minyard@acm.org>; Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>; Asmaa Mnebhi <Asmaa@mellanox.com>; Vadim Pasternak <vadimp@mellanox.com>; Corey Minyard <cminyard@mvista.com>; openipmi-developer@lists.sourceforge.net; linux-kernel@vger.kernel.org
Subject: [PATCH] ipmi: ipmb: don't allocate i2c_client on stack

The i2c_client structure can be fairly large, which leads to a warning about possible kernel stack overflow in some
configurations:

drivers/char/ipmi/ipmb_dev_int.c:115:16: error: stack frame size of 1032 bytes in function 'ipmb_write' [-Werror,-Wframe-larger-than=]

There is no real reason to even declare an i2c_client, as we can simply call i2c_smbus_xfer() directly instead of the i2c_smbus_write_block_data() wrapper.

Convert the ipmb_write() to use an open-coded i2c_smbus_write_block_data() here, without changing the behavior.

It seems that there is another problem with this implementation; when user space passes a length of more than I2C_SMBUS_BLOCK_MAX bytes, all the rest is silently ignored. This should probably be addressed in a separate patch, but I don't know what the intended behavior is here.

Fixes: 51bd6f291583 ("Add support for IPMB driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
drivers/char/ipmi/ipmb_dev_int.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/char/ipmi/ipmb_dev_int.c b/drivers/char/ipmi/ipmb_dev_int.c
index 2895abf72e61..c9724f6cf32d 100644
--- a/drivers/char/ipmi/ipmb_dev_int.c
+++ b/drivers/char/ipmi/ipmb_dev_int.c
@@ -117,7 +117,7 @@ static ssize_t ipmb_write(struct file *file, const char __user *buf, {
struct ipmb_dev *ipmb_dev = to_ipmb_dev(file);
u8 rq_sa, netf_rq_lun, msg_len;
- struct i2c_client rq_client;
+ union i2c_smbus_data data;
u8 msg[MAX_MSG_LEN];
ssize_t ret;

@@ -138,17 +138,17 @@ static ssize_t ipmb_write(struct file *file, const char __user *buf,

/*
* subtract rq_sa and netf_rq_lun from the length of the msg passed to
- * i2c_smbus_write_block_data_local
+ * i2c_smbus_xfer
*/
msg_len = msg[IPMB_MSG_LEN_IDX] - SMBUS_MSG_HEADER_LENGTH;
-
- strcpy(rq_client.name, "ipmb_requester");
- rq_client.adapter = ipmb_dev->client->adapter;
- rq_client.flags = ipmb_dev->client->flags;
- rq_client.addr = rq_sa;
-
- ret = i2c_smbus_write_block_data(&rq_client, netf_rq_lun, msg_len,
- msg + SMBUS_MSG_IDX_OFFSET);
+ if (msg_len > I2C_SMBUS_BLOCK_MAX)
+ msg_len = I2C_SMBUS_BLOCK_MAX;
+
+ data.block[0] = msg_len;
+ memcpy(&data.block[1], msg + SMBUS_MSG_IDX_OFFSET, msg_len);
+ ret = i2c_smbus_xfer(ipmb_dev->client->adapter, rq_sa, ipmb_dev->client->flags,
+ I2C_SMBUS_WRITE, netf_rq_lun,
+ I2C_SMBUS_BLOCK_DATA, &data);

return ret ? : count;
}
--
2.20.0
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