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 EB29B40860E; Tue, 7 Jul 2026 13:46:21 +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=1783431983; cv=none; b=nAW0epQK5LxhxO9gW0f3d55NJBEYVZxPPQhqsPMpDHPOwaMulz8ZI7Sg1M7pFveLB2wwe/B3CT2zwOsEWKaGqynA4hP+ZN248ajP7/1nzBSgd9aHwXCeT+6mrk0NzcgnPJ1Y2mfKkZXvhmZa19x/bO89WoCFuuDo3CguU3m2rOE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783431983; c=relaxed/simple; bh=beh7K05wSH/lp98tzrG3+yPBpvaD+6+uCfta4EDrejM=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=edursBmcAQZLXjo18oNq1ethCcr4JLrGBZN5sPQV9oC/NG9u1jN5hFnePB07nwKMZ3a1451Ya4t1i+n1hu28NcESUY5y6bLEndRDb036+Du2qM2bBVmGVUWoD20OeXlcayO4XkHcOtiHpfObHXHRuZ6ZGAS2SgSzXRF9Bca6UlU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IZpFqpTq; 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="IZpFqpTq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C1F961F00A3E; Tue, 7 Jul 2026 13:46:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783431980; bh=MtARyupKBSFTeggqMDtbHRlrQ4fC3iIQB6yfLh3wFqA=; h=Date:From:To:Cc:Subject:References; b=IZpFqpTqsWLVO9Uzpharapt7JTm855eIA5aYKxsjwIEuC1976sjK/utvhkmNSs8Cg m5SmIhnQb9zbq97k5vTrr4gLw6rl0Y8U/DcRQF1eXtNhZbFbJnKTf/sct7bZm9fngU dDKFm5E6t7Vd2oS9cNrIXvCzC52TclsL1ryBKJrmSP8BAbCDnvDgv8LXaKXXp2a/SU ZxYa7g9mP22kMZ6UsAVDlYUU1Bci5dM4W4RR1QUyUHklEI8YoLCugYhFO2146NIOaj RumVQb6tY60KBWExkc8KanLg8V1ntWWqlOAkvIPCgod5QfRiXG6BY4UwS4DIPBdFE/ 6gt1k/KU4N1fw== Received: from rostedt by gandalf with local (Exim 4.99.4) (envelope-from ) id 1wh680-00000000h34-0HKk; Tue, 07 Jul 2026 09:46:24 -0400 Message-ID: <20260707134623.914907495@kernel.org> User-Agent: quilt/0.69 Date: Tue, 07 Jul 2026 09:46:09 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , stable@vger.kernel.org, syzbot+2dd9d02f60775ce5c1fb@syzkaller.appspotmail.com, Yash Suthar Subject: [for-linus][PATCH 05/13] ring_buffer: Check page order under reader_lock References: <20260707134604.275787924@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: Yash Suthar When the ring_buffer_subbuf_order_set() is called the same time as the ring_buffer_read_page(), the wrong buffer->subbuf_size can be used as there is nothing keeping that in sync. This can cause an incorrect allocation and initialization that can cause a crash. Move the saving of the subbuf_size into a variable within the cpu_buffer->reader_lock, and use that throughout the function. The size only needs to be consistent throughout the allocation and initialization. If the buffer->subbuf_size changes when used, the reader data page will be found to be invalid and the read function will return an error (this is as expected). syzbot did not provide a reproducer for this crash, the race condition is logically sound and found via code inspection of the trace. Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260611151736.255767-1-yashsuthar983@gmail.com Fixes: bce761d75745 ("ring-buffer: Read and write to ring buffers with custom sub buffer size") Reported-by: syzbot+2dd9d02f60775ce5c1fb@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=2dd9d02f60775ce5c1fb Signed-off-by: Yash Suthar [ Rebased to 7.2-rc2 ] Signed-off-by: Steven Rostedt --- kernel/trace/ring_buffer.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index d9af2bbaf9c0..3ec173e22eeb 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -7070,6 +7070,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer, struct ring_buffer_event *event; struct buffer_data_page *dpage; struct buffer_page *reader; + unsigned int subbuf_size; long missed_events; unsigned int commit; unsigned int size; @@ -7092,15 +7093,22 @@ int ring_buffer_read_page(struct trace_buffer *buffer, if (!data_page || !data_page->data) return -1; - if (data_page->order != buffer->subbuf_order) - return -1; - dpage = data_page->data; if (!dpage) return -1; guard(raw_spinlock_irqsave)(&cpu_buffer->reader_lock); + /* + * Check data_page order under lock to prevent a race with a + * concurrent ring_buffer_subbuf_order_set() swap, which can + * cause an outofbounds memset() if the subbuf_size changes. + */ + if (data_page->order != buffer->subbuf_order) + return -1; + + subbuf_size = (PAGE_SIZE << data_page->order) - BUF_PAGE_HDR_SIZE; + reader = rb_get_reader_page(cpu_buffer); if (!reader) return -1; @@ -7226,7 +7234,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer, * missed events, then record it there. */ if (missed_events > 0 && - buffer->subbuf_size - size >= sizeof(missed_events)) { + subbuf_size - size >= sizeof(missed_events)) { memcpy(&dpage->data[size], &missed_events, sizeof(missed_events)); local_add(RB_MISSED_STORED, &dpage->commit); @@ -7246,8 +7254,8 @@ int ring_buffer_read_page(struct trace_buffer *buffer, /* * This page may be off to user land. Zero it out here. */ - if (size < buffer->subbuf_size) - memset(&dpage->data[size], 0, buffer->subbuf_size - size); + if (size < subbuf_size) + memset(&dpage->data[size], 0, subbuf_size - size); return read; } -- 2.53.0