[PATCH] i2c: fix stack buffer overflow vulnerability in i2c md command

[Tom Rini]

On Mon, Jun 27, 2022 at 06:33:01AM +0200, Heiko Schocher wrote:
> Hello Nicolas,
> 
> On 21.06.22 16:04, Nicolas IOOSS wrote:
> > Hello,
> > 
> > I sent some days ago the vulnerability fix below. I have not received any reply yet. Could a maintainer take a look at it, please?
> 
> Sorry for that, but I was on the road (embedded world in nuremberg).
> 
> > Best regards,
> > Nicolas
> > 
> > ------- Original Message -------
> > Le vendredi 10 juin 2022 à 4:50 PM, <nicolas.iooss.ledger at proton.me> a écrit :
> > 
> > 
> >> From: Nicolas Iooss nicolas.iooss+uboot at ledger.fr
> >>
> >>
> >> When running "i2c md 0 0 80000100", the function do_i2c_md parses the
> >> length into an unsigned int variable named length. The value is then
> >> moved to a signed variable:
> >>
> >> int nbytes = length;
> >> #define DISP_LINE_LEN 16
> >> int linebytes = (nbytes > DISP_LINE_LEN) ? DISP_LINE_LEN : nbytes;
> >>
> >> ret = dm_i2c_read(dev, addr, linebuf, linebytes);
> >>
> >> On systems where integers are 32 bits wide, 0x80000100 is a negative
> >> value to "nbytes > DISP_LINE_LEN" is false and linebytes gets assigned
> >>
> >> 0x80000100 instead of 16.
> >>
> >> The consequence is that the function which reads from the i2c device
> >> (dm_i2c_read or i2c_read) is called with a 16-byte stack buffer to fill
> >> but with a size parameter which is too large. In some cases, this could
> >> trigger a crash. But with some i2c drivers, such as drivers/i2c/nx_i2c.c
> >> (used with "nexell,s5pxx18-i2c" bus), the size is actually truncated to
> >> a 16-bit integer. This is because function i2c_transfer expects an
> >> unsigned short length. In such a case, an attacker who can control the
> >> response of an i2c device can overwrite the return address of a function
> >> and execute arbitrary code through Return-Oriented Programming.
> >>
> >> Fix this issue by using unsigned integers types in do_i2c_md. While at
> >> it, make also alen unsigned, as signed sizes can cause vulnerabilities
> >> when people forgot to check that they can be negative.
> >>
> >> Signed-off-by: Nicolas Iooss nicolas.iooss+uboot at ledger.fr
> >>
> >> ---
> >> cmd/i2c.c | 24 ++++++++++++------------
> >> 1 file changed, 12 insertions(+), 12 deletions(-)
> 
> Reviewed-by: Heiko Schocher <hs at denx.de>
> 
> @Tom: Should we add this to 2022.07? If so, feel free to pick it up,
>       thanks!

I'll pick this up directly along with the squashfs fix in the next day
or two, thanks.

-- 
Tom
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