linux-kernel - Re: [EXTERNAL] Re: audit: io_uring openat triggers audit reference count underflow in worker thread

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Message-ID: <MW2PR2101MB1033E52DD9307F9EF15F1E85F1CEA@MW2PR2101MB1033.namprd21.prod.outlook.com>
Date:   Mon, 9 Oct 2023 02:38:43 +0000
From:   Dan Clash <Dan.Clash@...rosoft.com>
To:     Paul Moore <paul@...l-moore.com>, Jens Axboe <axboe@...nel.dk>
CC:     "audit@...r.kernel.org" <audit@...r.kernel.org>,
        "io-uring@...r.kernel.org" <io-uring@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "brauner@...nel.org" <brauner@...nel.org>
Subject: Re: [EXTERNAL] Re: audit: io_uring openat triggers audit reference
 count underflow in worker thread

I retested with the following change as a sanity check:

-       BUG_ON(name->refcnt <= 0);
+       BUG_ON(atomic_read(&name->refcnt) <= 0);

checkpatch.pl suggests using WARN_ON_ONCE rather than BUG.

devvm ~ $ ~/linux/scripts/checkpatch.pl --patch ~/io_uring_audit_hang_atomic.patch 
WARNING: Do not crash the kernel unless it is absolutely unavoidable
  --use WARN_ON_ONCE() plus recovery code (if feasible) instead of BUG() or variants
#28: FILE: fs/namei.c:262:
+       BUG_ON(atomic_read(&name->refcnt) <= 0);
...

refcount_t uses WARN_ON_ONCE.

I can think of three choices:

1. Use atomic_t and remove the BUG line.
2. Use refcount_t and remove the BUG line. 
3. Use atomic_t and partially implement the warn behavior of refcount_t.

Choice 1 and 2 seem better than choice 3.