From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 94271483BC0; Thu, 27 Aug 2026 15:09:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787843365; cv=none; b=P7BFmadwPDWEp7Y4rvD4K/SAfnVLaP9vI6xslabs7QfFdXCZXJvmD04kzly1oNy4fgETKRxeav7bKQV8I1U627EUBAd8Bmzu6e4QGTkgWGov3HR+OEUV9GHjHNaE260RZ9bvV9THzERJw/2jAhI75Pqgudmik6ibSmnwszXRYA4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787843365; c=relaxed/simple; bh=rE9ONnbb64DmnGnBJPTYkqY0J4giVPlIuQ5Z+fpA4+g=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=SL65XPJG76UUANvW22cMAISbpyFKO7nQFS0joPlrH4MhOw5dnYgPYCjFhCQfApXDtVrHnJaJ+Vvl0whYrzLArB9Ij58VQcx+YDgABqgi5O+N2aHwRHGNg0dbfRuO4a+XjZvSeyldKiNzs3s+33PSRys5WAhTSp66w+Ho9caTJxc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gkfPyTx9; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="gkfPyTx9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 778EB1F00A3F; Thu, 27 Aug 2026 15:09:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787843363; bh=zyjyAs9XuohXcWHmBc/uGuYEOCdR4P0MDF3YsN/etfQ=; h=Date:From:To:Cc:Subject:References; b=gkfPyTx9Rm4YIxdb+n+U6v8o5UD4k//4Hjy2Unt5WkmBglKjo24E6DmZJmJLLILL1 Sst4R7kz0LpKU42qyItGkz3A27chHcP3LAGjBMuM1C/a5517wvVa99AqJnuoRRlBcL c4UH1Iie/gxhzxTCdqG+gKT0Ut3pEAhsuMt64upsqBGZU504mEro83FvprHeJTbeTw V2ROIXtIdxyN9XZ4HqsTMWUcHc5I8tm4pn/ZX7/06vq+hnzK4n6O6J4BGU+KBFiMLp FVcQ+hQjqBiq7+aovssRNC31XnmzAU2eRc//64cK5IjE18NA8wdbWHbGDhNcflR3kL TO+7+JhgosH/Q== Received: from rostedt by gandalf with local (Exim 4.99.4) (envelope-from ) id 1wzbk3-00000008PG0-1ZBc; Thu, 27 Aug 2026 11:10:11 -0400 Message-ID: <20260827151011.232932653@kernel.org> User-Agent: quilt/0.69 Date: Thu, 27 Aug 2026 11:09:53 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Deepanshu Kartikey , Haotian Zhang , Hui Su , Vincent Donnefort , stable@vger.kernel.org, syzbot+685955db58555575fdd2@syzkaller.appspotmail.com, Bradley Morgan Subject: [for-linus][PATCH 4/7] tracing: Fix use-after-free in trace_pipe read on sub-buffer order change References: <20260827150949.304280511@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 From: Deepanshu Kartikey Writing to buffer_subbuf_size_kb calls ring_buffer_subbuf_order_set(), which frees every sub-buffer of the ring buffer, including the reader page, and replaces them with newly allocated ones. Readers of trace_pipe hold pointers into those pages. ring_buffer_peek() looks up an event under cpu_buffer->reader_lock but returns the event pointer after dropping the lock, and peek_next_entry() then calls ring_buffer_event_length() and ring_buffer_event_data() on it. If the sub-buffer order is changed in that window, the reader dereferences freed memory: BUG: KASAN: use-after-free in ring_buffer_peek+0x3e0/0x430 Read of size 1 at addr ffff88802a4cf010 by task syz-executor989/6002 Freed by: free_buffer_page kernel/trace/ring_buffer.c:398 [inline] ring_buffer_subbuf_order_set+0x1325/0x18e0 kernel/trace/ring_buffer.c:7444 buffer_subbuf_size_write+0x182/0x280 kernel/trace/trace.c:8221 Take trace_access_lock(RING_BUFFER_ALL_CPUS) around the order change. This is the lock trace_pipe readers already hold across their entire peek-and-print loop, so the swap can no longer race with a reader that is dereferencing a peeked event. Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260817140655.5694-1-kartikey406@gmail.com Fixes: f9b94daa542a ("ring-buffer: Set new size of the ring buffer sub page") Reported-by: syzbot+685955db58555575fdd2@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=685955db58555575fdd2 Tested-by: syzbot+685955db58555575fdd2@syzkaller.appspotmail.com Reviewed-by: Bradley Morgan Signed-off-by: Deepanshu Kartikey Signed-off-by: Steven Rostedt --- kernel/trace/trace.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 740c5f358b75..60c87977f1e3 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -8214,6 +8214,8 @@ buffer_subbuf_size_write(struct file *filp, const char __user *ubuf, /* Do not allow tracing while changing the order of the ring buffer */ tracing_stop_tr(tr); + trace_access_lock(RING_BUFFER_ALL_CPUS); + old_order = ring_buffer_subbuf_order_get(tr->array_buffer.buffer); if (old_order == order) goto out; @@ -8253,6 +8255,7 @@ buffer_subbuf_size_write(struct file *filp, const char __user *ubuf, #endif (*ppos)++; out: + trace_access_unlock(RING_BUFFER_ALL_CPUS); if (ret) cnt = ret; tracing_start_tr(tr); -- 2.53.0