linux-kernel - Re: Buggy __free(kfree) usage pattern already in tree

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Date:   Fri, 15 Sep 2023 23:18:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        linux-kernel@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        akpm@...ux-foundation.org
Subject: Re: Buggy __free(kfree) usage pattern already in tree

On Fri, Sep 15, 2023 at 11:08:51PM +0200, Peter Zijlstra wrote:

> But a little later in that same function I then have:
> 
> 	do {
> 		struct rw_semaphore *exec_update_lock __free(up_read) = NULL;
> 		if (task) {
> 			err = down_read_interruptible(&task->signal->exec_update_lock);
> 			if (err)
> 				return err;
> 
> 			exec_update_lock = &task->signal->exec_update_lock;
> 
> 			if (!perf_check_permissions(&attr, task))
> 				return -EACCESS;
> 		}
> 
> 		... stuff serialized against exec *if* this is a task event ...
> 
> 	} while (0);
> 
> 
> And that might be a little harder to 'fix'.

Hmm, perhaps I can do a class for it and write the thing like:

	do {
		CLASS(cond_exec_update_lock, exec_lock_guard)(task); /* allow task == NULL */
		if (task && !exec_lock_guard)
			return -EINTR;

		if (task && !perf_check_permissions(&attr, task))
			return -EACCESS;

		... the rest ...

	} while (0);

that might be nicer..