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[104.155.91.135]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4994e99319bsm59638565e9.3.2026.08.05.12.15.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 Aug 2026 12:15:19 -0700 (PDT) Date: Wed, 5 Aug 2026 20:15:15 +0100 From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, linux-trace-kernel@vger.kernel.org Cc: mathieu.desnoyers@efficios.com, kernel-team@android.com, linux-kernel@vger.kernel.org, syzbot+e0cc44465d6bae735679@syzkaller.appspotmail.com Subject: Re: [PATCH] ring-buffer: Prevent subbuf order change when resizing is disabled Message-ID: References: <20260805153225.2096152-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Aug 05, 2026 at 05:36:51PM +0100, Vincent Donnefort wrote: > On Wed, Aug 05, 2026 at 04:32:24PM +0100, Vincent Donnefort wrote: > > Because ring_buffer_subbuf_order_set() frees buffer pages, we can't > > allow it when risizing is disabled. A non-consuming reader is at risk of > > use-after-free (rb_advance_iter()). > > > > Return -EBUSY on resize_disabled, matching ring_buffer_resize() > > behaviour. > > > > Fixes: f9b94daa542a ("ring-buffer: Set new size of the ring buffer sub page") > > Reported-by: syzbot+e0cc44465d6bae735679@syzkaller.appspotmail.com > > Signed-off-by: Vincent Donnefort > > > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > > index 8e2485bb3aa8..414bca2121a7 100644 > > --- a/kernel/trace/ring_buffer.c > > +++ b/kernel/trace/ring_buffer.c > > @@ -7358,7 +7358,7 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) > > > > cpu_buffer = buffer->buffers[cpu]; > > > > - if (cpu_buffer->mapped) { > > + if (atomic_read(&cpu_buffer->resize_disabled)) { > > Ha, my bad I forgot that mapped is not just "user-space mapped" but also > "range-mapped". > > However probably the best is just to record_disable range mapped buffers in > rb_allocate_cpu_buffer()... especially ring_buffer_resize() doesn't use > cpu_buffer->mapped I am also looking at the other findings from Sashiko. I believe some are legit. > > > err = -EBUSY; > > goto error; > > } > > > > base-commit: 075b74841bd0065a3bda3440873c747938e69b68 > > -- > > 2.55.0.571.g244d577d93-goog > > > > -- > Vincent -- Vincent