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 3E2403FA5EB; Tue, 7 Jul 2026 13:46:22 +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=1783431985; cv=none; b=QtTzuxu9YJNDxQyn4Th2Canv6YHSP6GDrL7s/YXCJ/fXtDkJADWkw3HFOo36nw8296s3M51xJch00AR9U8+bBgs6+5QdCPwvOtOox69dvHrcKImS1cR4PD/2RyemvOm3c9h4N9M2MpW2zSY8QpqGzhafOOygLWm/enLonq9sxe0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783431985; c=relaxed/simple; bh=94hcNEtcdvV7KVjsVbN/46mvskZkqtz5iAKp0+NYinY=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=i8DL7wzGQI5fSKd2szCWMQEyB5qtm934mEyCbEiHgiIZzTfPpNNlBIH/UZsvMv/O0yhRIiSQHbckabrXVSCCIHJ+jYLa5jd+B850lamPvfSLXIrMArUlF7kT7xII8Pd1aLB8u/lr/dcS5e0HTRxk+WTDPbj6Y76wnjRr7I6sjUw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=b/6CwTdO; 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="b/6CwTdO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 596211F00ADF; Tue, 7 Jul 2026 13:46:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783431981; bh=+2i7auYfxH+Wpn0TT15Yp87zPBX45q0Fv34N8u17wCw=; h=Date:From:To:Cc:Subject:References; b=b/6CwTdOO0w5S2Nv9w2dMlCDfCdhK4E24A2Urt7tYbPDfK6+GDym3tFYrtzP9tbXQ qqwDWMkWRuOKrhnGZ+h0flTFLnUxg7l4Jzo3KkDRerAEmcyNa99fhyCWcaMlpwXJMw aaPlr69cpuHUHRTBBLb/e3bpBOmLOER+4SlLKm5Q0Vo06OVpyrP0jyM8UIbb5BbnOT n43Ajq/rUpyOBBOAWYmf1pbljzSFVB00jKozpBuarfQIUYb7AI/8EspFJGWqWSJlRn v3FrBl+ymzMbPaO+dm2nysi2+4Buhc2oajhoarQJWQi+BIdvhHvMUFrFgyzma3US12 TVS5qAEqgoGwg== Received: from rostedt by gandalf with local (Exim 4.99.4) (envelope-from ) id 1wh680-00000000h4a-2aGU; Tue, 07 Jul 2026 09:46:24 -0400 Message-ID: <20260707134624.467637804@kernel.org> User-Agent: quilt/0.69 Date: Tue, 07 Jul 2026 09:46:12 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , stable@vger.kernel.org, Michael Bommarito , Beau Belgrave Subject: [for-linus][PATCH 08/13] tracing/user_events: Fix use-after-free of enabler in user_event_mm_dup() 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: Michael Bommarito user_event_enabler_destroy() removes an enabler from the per-mm mm->enablers list with list_del_rcu() and then frees it immediately with kfree(). That list is walked locklessly by user_event_mm_dup() during fork(), under rcu_read_lock() only: rcu_read_lock(); list_for_each_entry_rcu(enabler, &old_mm->enablers, mm_enablers_link) ... user_event_mm_dup() does not take event_mutex. The per-enabler destroy path user_events_ioctl_unreg() (DIAG_IOCSUNREG) takes event_mutex but nothing that excludes the dup walk. Threads that share an mm share one user_event_mm and one enabler list, so an unregister on one thread can free an enabler while another thread is forking and user_event_mm_dup() is mid-walk. The walk then dereferences the freed enabler (for example enabler->event in user_event_enabler_dup()). This is reachable by an unprivileged task that can open user_events_data: a single multithreaded process that registers an enabler and then concurrently unregisters it and calls fork() triggers the race. KASAN reports a slab-use-after-free read in user_event_enabler_dup() called from user_event_mm_dup() and copy_process() during clone(); with kasan.fault=panic the kernel panics. Free the enabler after a grace period with kfree_rcu(), matching the list_del_rcu() removal and the rcu_read_lock() readers in user_event_mm_dup(). Add an rcu_head to struct user_event_enabler for this. The error path in user_event_enabler_create() keeps using kfree() because that enabler is freed before it is published to the RCU list. Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260618222743.538915-1-michael.bommarito@gmail.com Fixes: 7235759084a4 ("tracing/user_events: Use remote writes for event enablement") Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Michael Bommarito Acked-by: Beau Belgrave Signed-off-by: Steven Rostedt --- kernel/trace/trace_events_user.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c index c4ba484f7b38..412ca1e3a40c 100644 --- a/kernel/trace/trace_events_user.c +++ b/kernel/trace/trace_events_user.c @@ -109,6 +109,9 @@ struct user_event_enabler { /* Track enable bit, flags, etc. Aligned for bitops. */ unsigned long values; + + /* Defer free so RCU list readers (user_event_mm_dup) are safe. */ + struct rcu_head rcu; }; /* Bits 0-5 are for the bit to update upon enable/disable (0-63 allowed) */ @@ -404,7 +407,12 @@ static void user_event_enabler_destroy(struct user_event_enabler *enabler, /* No longer tracking the event via the enabler */ user_event_put(enabler->event, locked); - kfree(enabler); + /* + * The enabler is removed from an RCU-traversed list + * (user_event_mm_dup walks mm->enablers under rcu_read_lock only), + * so the backing memory must outlive a grace period. + */ + kfree_rcu(enabler, rcu); } static int user_event_mm_fault_in(struct user_event_mm *mm, unsigned long uaddr, -- 2.53.0