Query Regarding Stack-Out-of-Bounds Error

Muni Sekhar
2024-08-26T12:34:51Z

Dear Linux Kernel Community,

I am writing to seek clarification on a potential stack-out-of-bounds
issue observed during the calls to for_each_set_bit function or
find_first_bit function, specifically in the following code snippet:

static struct cmd_info *find_cmd_entry_any_ring(struct intel_gvt *gvt,
unsigned int opcode, int rings)
{
struct cmd_info *info = NULL;
unsigned int ring;
...
for_each_set_bit(ring, (unsigned long *)&rings, I915_NUM_ENGINES) {

In the above code, a 32-bit integer pointer (rings) is being cast to a
64-bit unsigned long pointer, which leads to an extra 4 bytes being
accessed. This raises a concern regarding a stack-out-of-bounds bug.

My specific query is: While it is logically understandable that a
write operation involving these extra 4 bytes could cause a kernel
crash, in this case, it is a read operation that is occurring. Would
such a read operation still be capable of crashing the kernel or
resulting in unpredictable system behaviour? If so, could you please
explain how that would happen?

I appreciate your insights and look forward to your guidance on this issue.

--
Thanks,
Sekhar