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i2c: fix stack buffer overflow vulnerability in i2c md command

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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@ledger.fr>
Reviewed-by: Heiko Schocher <hs@denx.de>
This commit is contained in:
Nicolas Iooss 2022-06-10 14:50:25 +00:00 committed by Tom Rini
parent b75fd37037
commit 8f8c04bf1e
1 changed files with 12 additions and 12 deletions
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24
cmd/i2c.c
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@ -200,10 +200,10 @@ void i2c_init_board(void)
*
* Returns the address length.
*/
static uint get_alen(char *arg, int default_len)
static uint get_alen(char *arg, uint default_len)
{
int j;
int alen;
uint j;
uint alen;
alen = default_len;
for (j = 0; j < 8; j++) {
@ -247,7 +247,7 @@ static int do_i2c_read(struct cmd_tbl *cmdtp, int flag, int argc,
{
uint chip;
uint devaddr, length;
int alen;
uint alen;
u_char *memaddr;
int ret;
#if CONFIG_IS_ENABLED(DM_I2C)
@ -301,7 +301,7 @@ static int do_i2c_write(struct cmd_tbl *cmdtp, int flag, int argc,
{
uint chip;
uint devaddr, length;
int alen;
uint alen;
u_char *memaddr;
int ret;
#if CONFIG_IS_ENABLED(DM_I2C)
@ -469,8 +469,8 @@ static int do_i2c_md(struct cmd_tbl *cmdtp, int flag, int argc,
{
uint chip;
uint addr, length;
int alen;
int j, nbytes, linebytes;
uint alen;
uint j, nbytes, linebytes;
int ret;
#if CONFIG_IS_ENABLED(DM_I2C)
struct udevice *dev;
@ -589,9 +589,9 @@ static int do_i2c_mw(struct cmd_tbl *cmdtp, int flag, int argc,
{
uint chip;
ulong addr;
int alen;
uint alen;
uchar byte;
int count;
uint count;
int ret;
#if CONFIG_IS_ENABLED(DM_I2C)
struct udevice *dev;
@ -676,8 +676,8 @@ static int do_i2c_crc(struct cmd_tbl *cmdtp, int flag, int argc,
{
uint chip;
ulong addr;
int alen;
int count;
uint alen;
uint count;
uchar byte;
ulong crc;
ulong err;
@ -985,7 +985,7 @@ static int do_i2c_loop(struct cmd_tbl *cmdtp, int flag, int argc,
char *const argv[])
{
uint chip;
int alen;
uint alen;
uint addr;
uint length;
u_char bytes[16];