linux-kernel - Advantages of crashing if someone is freeing NULL pointer.

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Message-ID: <CAFf+5zgU2A4PmOm06Ca654UgLErJbfMTK5XhnR5X2D0Jz2J-SA@mail.gmail.com>
Date: Fri, 31 Jan 2025 13:51:19 +0530
From: Amit <amitchoudhary0523@...il.com>
To: linux-kernel@...r.kernel.org
Subject: Advantages of crashing if someone is freeing NULL pointer.

Hi,

kfree(NULL) doesn't crash. If kfree(NULL) crashes then we can get few
advantages.

Let's say that we do the following:

kfree(x);
x = NULL;

Now, if someone uses 'x' again then it will crash. Also, if someone
does double free of 'x' again then also the kernel will crash. So, we
can solve two problems in one shot.

The side-effect is that the code now will become:

if (x) {
  kfree(x);
  x = NULL;
}

This will introduce a few more instructions, probably 10 instructions
but 10 extra instructions per kfree() should not slow down the kernel.
I don't think we are calling kfree() very frequently.

If people agree with me then I can make the necessary changes and send a patch.

If people here agree with me then I will also try to get free(NULL) to
crash in the C library - I will talk to them and send a patch if they
agree. But first, I wanted to see if people here agree with me or not.

Regards,
Amit