Dear Linux Developers for SCSI Driver,
We are curious about the functionality of `st_setup`
(https://elixir.bootlin.com/linux/latest/source/drivers/scsi/st.c#L4102).
```
static int __init st_setup(char *str)
{
int i, len, ints[5];
char *stp;
stp = get_options(str, ARRAY_SIZE(ints), ints);
if (ints[0] > 0) {
for (i = 0; i < ints[0] && i < ARRAY_SIZE(parms); i++)
if (parms[i].val)
*parms[i].val = ints[i + 1];
}
...
}
```
For this function, we are trying to understand how it works but not
sure whether it would be an out-of-bound read.
The length of both `ints` and `parms` is 5 (the latterdefined at
https://elixir.bootlin.com/linux/latest/source/drivers/scsi/st.c#L125).
Thus, when `ints[0]` is 5, we could assign `ints[5]`
(out-of-bound-read) to `parms[4].val`. Based on our understanding of
the `get_options` function
(https://elixir.bootlin.com/linux/latest/source/lib/cmdline.c#L107),
it could be possible that `ints[0] == 5`, where the first element of
`ints` indicates the number of parsed options. Hence, it is possible
to do
a out-of-bound read once `debug_flag` is enabled (to pass `if
(parms[i].val)`).
Please correct us if we miss some key prerequisites for this function
or the data structure.
Thanks in advance!
Based on our understanding, the possible fix could be
```
int i, len, ints[6];
```
which allocates `len(parms) + 1` for `ints`.
Best,
Chenyuan
On 12. Mar 2024, at 16.43, Chenyuan Yang <[email protected]> wrote:
>
> Dear Linux Developers for SCSI Driver,
>
> We are curious about the functionality of `st_setup`
> (https://elixir.bootlin.com/linux/latest/source/drivers/scsi/st.c#L4102).
>
> ```
> static int __init st_setup(char *str)
> {
> int i, len, ints[5];
> char *stp;
>
> stp = get_options(str, ARRAY_SIZE(ints), ints);
>
> if (ints[0] > 0) {
> for (i = 0; i < ints[0] && i < ARRAY_SIZE(parms); i++)
> if (parms[i].val)
> *parms[i].val = ints[i + 1];
> }
> ...
> }
> ```
>
> For this function, we are trying to understand how it works but not
> sure whether it would be an out-of-bound read.
>
> The length of both `ints` and `parms` is 5 (the latterdefined at
> https://elixir.bootlin.com/linux/latest/source/drivers/scsi/st.c#L125).
> Thus, when `ints[0]` is 5, we could assign `ints[5]`
> (out-of-bound-read) to `parms[4].val`. Based on our understanding of
> the `get_options` function
> (https://elixir.bootlin.com/linux/latest/source/lib/cmdline.c#L107),
> it could be possible that `ints[0] == 5`, where the first element of
> `ints` indicates the number of parsed options. Hence, it is possible
> to do
> a out-of-bound read once `debug_flag` is enabled (to pass `if
> (parms[i].val)`).
>
I think your analysis is correct and there is a bug.
> Please correct us if we miss some key prerequisites for this function
> or the data structure.
> Thanks in advance!
>
> Based on our understanding, the possible fix could be
> ```
> int i, len, ints[6];
> ```
> which allocates `len(parms) + 1` for `ints`.
Yes, this would fix the bug. However, it might be better to define
size of ints[] as ARRAY_SIZE(parms)+1 to connect the size directly
to the definition of parameters.
(The bug applies to the case where st is compiled into the kernel
and a list of integers is used to define the options. Not a common
case, but a bug should be fixed.)
Thanks,
Kai