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Sun, 25 Jan 2026 17:58:09 -0800 (PST) Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20260125075302.621785-1-1599101385@qq.com> In-Reply-To: From: clingfei Date: Mon, 26 Jan 2026 09:57:57 +0800 X-Gm-Features: AZwV_QjVeqCMP2y42w74OhOqiz7WcILKHlLOMnQCXg0q-cI8oNehyDgCFFkBcAI Message-ID: Subject: Re: [PATCH] io_uring: gate personality per opcode to fix TOCTOU check in io_msg_ring_prep To: Jens Axboe Cc: io-uring@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Jens Axboe =E4=BA=8E2026=E5=B9=B41=E6=9C=8825=E6=97=A5=E5= =91=A8=E6=97=A5 22:16=E5=86=99=E9=81=93=EF=BC=9A > > On 1/25/26 12:53 AM, clingfei wrote: > > From: Cheng Lingfei > > > > Add allow_personality io_issue_def and reject personality use in > > io_init_req for opcodes that do not permit it. This fixes a TOCTOU > > window in the prior implementation: userspace could race-update > > sqe->personality and bypass the __io_msg_ring_prep personality check. > > Please do detail what the bug is here, this looks like some kind of > AI hallucination. The check in msg_ring prep exists just to reject > commands with it set, for future expansion. The only thing that > matters is the ordering and use in io_init_req(), which is fine. > > -- > Jens Axboe > Sorry, I forgot to reply to all in the previous email. The io_init_req checks sqe->personality; if personality is not zero, req->creds is initialized based on personality. The msg_ring prep also chec= ks sqe->personality and rejects non-zero personality values. However, sqe is shared between the kernel and userspace. This means a user can submit a msg_ring SQE with a non-zero personality. After passing the check in io_init_req, the user process can concurrently modify personality to set it to 0, thus enabling it to pass the check in msg_ring prep and invalidating its rejection of non-zero `personality` values. This is not an AI hallucination, and it can be demonstrated by a userspace = PoC.