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 1AB01257ACF; Sun, 30 Aug 2026 01:05:34 +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=1788051936; cv=none; b=RMn7WCR4nfSy+ZUHKvrSFwfa/0owb4a/Mc/a7GrY05Tpfg9VgZ7RH7deMFxLaQm+p4bkMW3iB3fg0CCK6gA5ZfyzEbtuooz3cg5z00Tyk5mGs92qJdAkDYRCWy8K3BheQyzPmQv6y7SUzpBDH93cCusJbQ4CRM9Z6hlSeibj0A4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788051936; c=relaxed/simple; bh=OQWyxaqu7DKBUM1SGG6Os5vGlC0Ne03Ma6gC/0wHa4g=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=Et1R4e9pwEqNB/15E/+SJroWAQvwe1DU/wrVNnOYHeEJpyAUBROC5vHGNlZENtfiLkQ01YrcmKphgG+9tdcGD9wcCDElo0gC33Q6MGNPqvpxPCmbMM0OdfofhxUPXfEgUe+85TbYmsyjGFOo56XsxgH9UBm+fsiwZWMtNZWXBFc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZMU0NLJm; 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="ZMU0NLJm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D54E41F00A3D; Sun, 30 Aug 2026 01:05:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788051934; bh=UYxcBK6fM1KuMpSUtPj8kSRAS7+FWYTJ6/yqMO5ljB4=; h=Date:From:To:Cc:Subject:References; b=ZMU0NLJmnlx3hNphremnTG+0Amaqr19RtxgrT44wu+OJZUwgzf4tMkksbX/qRWOvm lzbuJzUwufqkyFlBa81ZibegWwIHReOoSL/NB7iwnagFXj3buPCRDwcIdxmMZddd/8 39eYuRW8mW4sEn3XoPNs2ui8KmigyrZrDXEV0pkyrjlS5uHhZ6NqnqklNg8kKQfBm2 +OoqXHKgwPUsXBLjKZE2S6tDgBNU3HrvgJ7EJkEh2Kbtnrecj5uo/ZPEUEMKBLBK5A ono2NVJbPwM3t1B+eIp3oWkXrHejkZzrr1ezQZfSUTfwkXKQ+7kGarI8mn3RmHtPXl g6hcq/Z1LEtMg== Received: from rostedt by gandalf with local (Exim 4.99.4) (envelope-from ) id 1x0U0C-0000000A490-07mR; Sat, 29 Aug 2026 21:06:28 -0400 Message-ID: <20260830010627.875981502@kernel.org> User-Agent: quilt/0.69 Date: Sat, 29 Aug 2026 21:05:32 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort , stable@vger.kernel.org, =?UTF-8?q?J=C3=A9r=C3=A9my=20Jean?= , Bradley Morgan Subject: [for-linus][PATCH 1/3] tracing/user_events: Clear copied tracing state before fork duplication References: <20260830010531.847108845@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: =?UTF-8?q?J=C3=A9r=C3=A9my=20Jean?= dup_task_struct() copies user_event_mm from the parent into the child, without grabbing a reference to it. user_event_mm_dup() should replace it, but it leaves that copied pointer unmodified if user_event_mm_alloc() fails. When the child exits, user_event_mm_remove() decrements a reference the child never owned, which ultimately frees user_event_mm, while the parent still as a stale pointer to it. This creates a UAF, which KASAN reports as: BUG: KASAN: slab-use-after-free in current_user_event_mm+0x51/0x1d0 Write of size 4 at addr ffff888005010d30 by task init/44 Call Trace: kasan_report+0xce/0x100 kasan_check_range+0x10f/0x1e0 current_user_event_mm+0x51/0x1d0 user_events_ioctl+0x82e/0x15c0 __x64_sys_ioctl+0x139/0x1c0 do_syscall_64+0xce/0x450 entry_SYSCALL_64_after_hwframe+0x77/0x7f Allocated by task 44: __kasan_kmalloc+0x8f/0xa0 __kmalloc_cache_noprof+0x180/0x3a0 user_event_mm_alloc+0x3c/0x1f0 current_user_event_mm+0x88/0x1d0 Freed by task 42: __kasan_slab_free+0x43/0x70 kfree+0x13a/0x390 process_one_work+0x696/0xf90 worker_thread+0x420/0xba0 The fix simply clears the copied pointer before any possible failure. In case of failure, the child then has nothing to free. Cc: stable@vger.kernel.org Fixes: 7235759084a4 ("tracing/user_events: Use remote writes for event enablement") Link: https://patch.msgid.link/20260827184321.2964601-2-Jeremy.Jean@oss.cyber.gouv.fr Assisted-by: Codex:gpt-5 Signed-off-by: Jérémy Jean Reviewed-by: Bradley Morgan Signed-off-by: Steven Rostedt --- kernel/trace/trace_events_user.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c index 2bbc89d4a266..93cda2f6f269 100644 --- a/kernel/trace/trace_events_user.c +++ b/kernel/trace/trace_events_user.c @@ -868,6 +868,9 @@ void user_event_mm_dup(struct task_struct *t, struct user_event_mm *old_mm) struct user_event_mm *mm = user_event_mm_alloc(t); struct user_event_enabler *enabler; + /* On failure, do not free parent's copy */ + t->user_event_mm = NULL; + if (!mm) return; -- 2.53.0