linux-kernel - Query Regarding Stack-Out-of-Bounds Error

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Message-ID: <CAHhAz+hjhZQnTWX088EmMDbszAJrrBQBqkhvfiMjxQPNtWbkqw@mail.gmail.com>
Date: Mon, 26 Aug 2024 18:04:39 +0530
From: Muni Sekhar <munisekharrms@...il.com>
To: kernelnewbies <kernelnewbies@...nelnewbies.org>
Cc: LKML <linux-kernel@...r.kernel.org>
Subject: Query Regarding Stack-Out-of-Bounds Error

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