Hi Greg, Linus, all,
I just hit a buffer overflow while playing around with i2cdump and
i2c-viapro through i2c-dev. This is caused by a missing length check on
a buffer operation when doing a SMBus block read in the i2c-viapro
driver. The problem was already known and had been fixed upon report by
Sergey Vlasov back in August 2003 in lm_sensors (2.4 kernel version of
the driver) but for some reason it was never ported to the 2.6 kernel
version.
I am not a security expert but I would guess that such a buffer overflow
could possibly be used to run arbitrary code in kernel space from user
space through i2c-dev. The severity obviously depends on the permisions
set on the i2c device files in /dev. Maybe it wouldn't be a bad idea to
push this patch upstream rather sooner than later.
While I was at it, I also changed a similar size check (for SMBus block
write this time) in the same driver to use the correct constant
I2C_SMBUS_BLOCK_MAX instead of its current numerical value. This doesn't
change a thing at the moment but prevents another potential buffer
overflow in case the value of I2C_SMBUS_BLOCK_MAX were to be changed in
the future (admittedly unlikely though).
Thanks.
Signed-off-by: Jean Delvare <[EMAIL PROTECTED]>
--- linux-2.6.11-rc1-bk8/drivers/i2c/busses/i2c-viapro.c.orig 2005-01-21
20:05:05.000000000 +0100
+++ linux-2.6.11-rc1-bk8/drivers/i2c/busses/i2c-viapro.c 2005-01-25
21:45:01.000000000 +0100
@@ -233,8 +233,8 @@
len = data->block[0];
if (len < 0)
len = 0;
- if (len > 32)
- len = 32;
+ if (len > I2C_SMBUS_BLOCK_MAX)
+ len = I2C_SMBUS_BLOCK_MAX;
outb_p(len, SMBHSTDAT0);
i = inb_p(SMBHSTCNT); /* Reset SMBBLKDAT */
for (i = 1; i <= len; i++)
@@ -268,6 +268,8 @@
break;
case VT596_BLOCK_DATA:
data->block[0] = inb_p(SMBHSTDAT0);
+ if (data->block[0] > I2C_SMBUS_BLOCK_MAX)
+ data->block[0] = I2C_SMBUS_BLOCK_MAX;
i = inb_p(SMBHSTCNT); /* Reset SMBBLKDAT */
for (i = 1; i <= data->block[0]; i++)
data->block[i] = inb_p(SMBBLKDAT);
--
Jean Delvare
http://khali.linux-fr.org/
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